{"id":206410,"date":"1999-07-15T10:44:19","date_gmt":"1999-07-15T14:44:19","guid":{"rendered":"https:\/\/news.harvard.edu\/gazette\/?p=206410"},"modified":"2024-01-19T11:42:56","modified_gmt":"2024-01-19T16:42:56","slug":"human-biological-clock-set-back-an-hour","status":"publish","type":"post","link":"https:\/\/news.harvard.edu\/gazette\/story\/1999\/07\/human-biological-clock-set-back-an-hour\/","title":{"rendered":"Human Biological Clock Set Back an Hour"},"content":{"rendered":"\n\t\n\t
\n\t\t\t\n\t\t\tCampus & Community\t\t<\/a>\n\t\t\n\t\t

\n\t\tHuman biological clock set back an hour\t<\/h1>\n\n\t\n\t\n\t
\n\t\t
\n\t\t\t
\n\t\t\t\t\t

\n\t\tWilliam J. Cromie\t<\/p>\n\t\t\t

\n\t\t\tGazette Staff\t\t<\/p>\n\t\t\t\t\t<\/address>\n\t\t<\/div>\n\n\t\t

\n
\"\"
A. Czeisler and his colleagues have made the most accurate measurements to date of human daily rhythms.\t\t\t<\/figcaption><\/figure>\n\n\n\n

The internal clock that drives the daily activities of all living things,
\nfrom wild flowers to whales, is wound by Earth\u2019s rotation. The 24-hour
\ncycle, tied to one turn of the planet on its axis, embodies a biological
\nclock mimicked by timepieces invented to measure the human day.<\/p>\n\n\n\n

But these external clocks don\u2019t exactly match the biological
\ntickings inside ourselves. Many measurements led to the conclusion that the
\ninternal clock period is actually closer to 25 hours; that is, the biological
\nclock was thought to drift toward a 25-hour day unless it is set back an hour
\neach day by exposure to morning light and to external clocks. This situation is
\nblamed for a long list of sleep problems.<\/p>\n\n\n\n

Now, the most accurate measurements to date, made by researchers at
\nHarvard University, reveal that our natural daily rhythm is much closer to that
\nof other living things than previously believed. The better match opens the way
\nfor experts to more effectively treat sleep problems involving night work, jet
\nlag, Earth-orbiting astronauts, or just not being able to go to sleep and wake
\nup on time.<\/p>\n\n\n\n

By recording the daily rhythms of hormones and body temperatures in 24
\nhealthy young and old men and women over a one-month period, the researchers
\nconclude that our internal clocks run on a daily cycle of 24 hours, 11
\nminutes.<\/p>\n\n\n\n

“That\u2019s slightly longer than 24 hours, but significantly
\nshorter than past estimates of 25 hours,” says Charles Czeisler, professor
\nof medicine at the Harvard Medical School. “Researchers previously reported
\na range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation
\nbetween our subjects, with a 95 percent level of confidence, was no more than
\nplus or minus 16 minutes, a remarkably small range.”<\/p>\n\n\n\n

“These data reveal that the human circadian pacemaker is as stable
\nand precise in measuring time as that of other mammals,” notes Richard
\nKronauer, Gordon McKay Professor of Mechanical Engineering. “These results
\napply to both young and older people, and have practical implications for
\nunderstanding and developing treatments for sleep disorders tied to circadian
\n[daily] rhythms.”<\/p>\n\n\n\n

Czeisler, Kronauer, and colleagues reported their findings in the June 25
\nissue of Science<\/i> magazine. Co-authors of the report include Emery Brown,
\nassistant professor of anesthesia; Derk-Jan Dijk, assistant professor of
\nmedicine, and research fellow Jeanne Duffy, all of the Harvard Medical
\nSchool.<\/p>\n\n\n\n

28-Hour Days<\/strong><\/p>\n\n\n\n

“It was both surprising and reassuring that the human clock runs
\nwith the same precision as that of other living things,” Czeisler comments.
\n“But we did not expect to find that both young and old people have the same
\ndaily period.”<\/p>\n\n\n\n

Many experts believe that the clock speeds up with age, and they use that
\nidea to explain why elders wake up earlier in the morning. With that idea now
\nput to bed, researchers need to come up with new theories for these early
\nawakenings.<\/p>\n\n\n\n

Why are these measurements more accurate than previous ones?<\/p>\n\n\n\n

“Other investigators used elaborate procedures to shield subjects
\nfrom time cues and the outside world,” answers Czeisler, who is also
\ndirector of circadian and sleep disorders medicine at Brigham and Women\u2019s
\nHospital in Boston. “They even coiled copper wire around the rooms in which
\npeople were isolated to counteract natural electromagnetic fields. However,
\nthese experimenters allowed their subjects to switch on lights when they were
\nawake and turn them off when they wanted to sleep. They didn\u2019t think this
\nwould have any effect, but switching on electric lights resets the biological
\nclock. It\u2019s the same as resetting your watch.”<\/p>\n\n\n\n

Kronauer calculated that changing ordinary room light in such experiments
\ncan shift the apparent circadian cycle by more than 40 minutes.<\/p>\n\n\n\n

The Harvard team had their subjects go to bed four hours later each day,
\neffectively creating a 28-hour day. This strategy disconnected the biological
\npacemaker from clock time.<\/p>\n\n\n\n

“The 28-hour cycle distributed light exposure, sleep and
\nwakefulness, work and play evenly around the biological clock,” explains
\nCzeisler. “The men and women did not get light exposure at the same time
\neach clock day. Instead, they experienced a six-day week in which light and dark
\noccurred at different times each day.”<\/p>\n\n\n\n

This altered schedule freed their internal clocks from the sleep-wake
\ncycle and allowed them to tick at the natural period. Despite six-day weeks,
\ntheir body temperatures and hormone secretions went through seven cycles every
\nweek. Sleepiness was tied to a drop in core body temperature and to an increase
\nin melatonin, a hormone secreted by the pineal gland and sold over-the-counter
\nas a sleeping pill.<\/p>\n\n\n\n

Czeisler\u2019s crew also measured changes in cortisol, a hormone
\ninvolved in metabolism and other basic body functions. Cortisol naturally drops
\nto its lowest levels at bedtime and reaches its highest point during early
\nwaking hours.<\/p>\n\n\n\n

The result was clear. No matter when the subjects went to bed or got up,
\nand whatever they did while awake, body temperature and hormones rose and fell
\non an average cycle of 24 hours and 11 minutes.<\/p>\n\n\n\n

What do people do when isolated in a timeless room for a month? Some of
\nthem were graduate students, and they worked on various school projects or wrote
\ntheir dissertations. Others did oil paintings or busied themselves with jigsaw
\npuzzles. One man, a geologist, brought his rock collection and chipped the time
\naway with a rock hammer. Yet others read, thought about the world, and enjoyed
\nthe phoneless, e-mailless solitude.<\/p>\n\n\n\n

Rethinking Biological Time<\/strong><\/p>\n\n\n\n

Czeisler, Kronauer, and some colleagues first presented the case for
\na near-24-hour biological clock in 1989. “The many years of experiments
\ndone since then, including this latest work, makes us confident in the accuracy
\nof our measurements,” Czeisler says.<\/p>\n\n\n\n

Apparently, Earth\u2019s rotation impresses a 24-hour period on the genes
\nof humans and other living things. <\/b>The human clock consists of a cluster
\nof nerve cells (the suprachiasmtic nucleus) barely a hundredth of an inch in
\nsize, located deep in the brain and connected to the eyes\u2019 optic
\nnerves.<\/p>\n\n\n\n

“Accepting the near-24-hour period means that all the ideas about
\ndaily human rhythms that we take for granted must be rethought,” Czeisler
\nsays. For example, biological clock lore states that we drift to a later wake-up
\nhour on weekends because we fail to reset the 25-hour cycle each morning as we
\ngo to work.<\/p>\n\n\n\n

“We\u2019re not drifting,” Czeisler insists. “We\u2019re
\npushing ourselves to a later time with our exposure to electric lights from
\nsunset to bedtime. That resets our biological clocks.”<\/p>\n\n\n\n

The resetting, which leads to difficulty in awakening on Monday, can, in
\nmany cases, be “cured” by going to bed earlier on weekends. Awakening
\ntoo early often can be avoided by going to bed later.<\/p>\n\n\n\n

To deal with night-shift work, jet lag, sleeping in an orbiting
\nspacecraft, or the winter blues, our biological clocks can be reset by timed
\nexposure to bright light. “To determine the correct exposure, however, we
\nmust pin down the internal circadian period, the natural rhythm of our
\nbodies,” Czeisler points out. “Now, we are able to do this more
\neffectively than before.”<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

The internal clock that drives the daily activities of all living things, from wild flowers to whales, is wound by Earth\u2019s rotation. The 24-hour cycle, tied to one turn of…<\/p>\n","protected":false},"author":108097152,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"gz_ga_pageviews":64,"gz_ga_lastupdated":"2022-05-16 11:39","document_color_palette":null,"author":"William J. 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biological clock set back an hour\t<\/h1>\n\n\t\n\t\n\t<div class=\"article-header__meta\">\n\t\t<div class=\"wp-block-post-author\">\n\t\t\t<address class=\"wp-block-post-author__content\">\n\t\t\t\t\t<p class=\"author wp-block-post-author__name\">\n\t\tWilliam J. Cromie\t<\/p>\n\t\t\t<p class=\"wp-block-post-author__byline\">\n\t\t\tGazette Staff\t\t<\/p>\n\t\t\t\t\t<\/address>\n\t\t<\/div>\n\n\t\t<time class=\"article-header__date\" datetime=\"1999-07-15\">\n\t\t\tJuly 15, 1999\t\t<\/time>\n\n\t\t<span class=\"article-header__reading-time\">\n\t\t\t6 min read\t\t<\/span>\n\t<\/div>\n\n\t\t\t<\/div>\n\t\t\n\t\n<\/header>\n"},"2":{"blockName":"core\/group","attrs":{"templateLock":false,"metadata":{"name":"Article content"},"align":"wide","layout":{"type":"constrained","justifyContent":"center"},"tagName":"div","lock":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","ariaLabel":"","anchor":""},"innerBlocks":[{"blockName":"core\/image","attrs":{"align":"right","id":206411,"sizeSlug":"full","className":"is-resized","blob":"","url":"https:\/\/news.harvard.edu\/gazette\/wp-content\/uploads\/2016\/09\/bioclock.jpg","alt":"","caption":"A. Czeisler and his colleagues have made the most accurate measurements to date of human daily rhythms.\t\t\t","lightbox":[],"title":"","href":"","rel":"","linkClass":"","width":"","height":"","aspectRatio":"","scale":"","linkDestination":"","linkTarget":"","lock":[],"metadata":[],"style":[],"borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<figure class=\"wp-block-image alignright size-full is-resized\"><img src=\"https:\/\/news.harvard.edu\/gazette\/wp-content\/uploads\/2016\/09\/bioclock.jpg\" alt=\"\" class=\"wp-image-206411\"\/><figcaption class=\"wp-element-caption\">A. Czeisler and his colleagues have made the most accurate measurements to date of human daily rhythms.\t\t\t<\/figcaption><\/figure>\n","innerContent":["\n<figure class=\"wp-block-image alignright size-full is-resized\"><img src=\"https:\/\/news.harvard.edu\/gazette\/wp-content\/uploads\/2016\/09\/bioclock.jpg\" alt=\"\" class=\"wp-image-206411\"\/><figcaption class=\"wp-element-caption\">A. Czeisler and his colleagues have made the most accurate measurements to date of human daily rhythms.\t\t\t<\/figcaption><\/figure>\n"],"rendered":"\n<figure class=\"wp-block-image alignright size-full is-resized\"><img src=\"https:\/\/news.harvard.edu\/gazette\/wp-content\/uploads\/2016\/09\/bioclock.jpg\" alt=\"\" class=\"wp-image-206411\"\/><figcaption class=\"wp-element-caption\">A. Czeisler and his colleagues have made the most accurate measurements to date of human daily rhythms.\t\t\t<\/figcaption><\/figure>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"The internal clock that drives the daily activities of all living things,<br>\nfrom wild flowers to whales, is wound by Earth\u2019s rotation. The 24-hour<br>\ncycle, tied to one turn of the planet on its axis, embodies a biological<br>\nclock mimicked by timepieces invented to measure the human day.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>The internal clock that drives the daily activities of all living things,<br>\nfrom wild flowers to whales, is wound by Earth\u2019s rotation. The 24-hour<br>\ncycle, tied to one turn of the planet on its axis, embodies a biological<br>\nclock mimicked by timepieces invented to measure the human day.<\/p>\n","innerContent":["\n<p>The internal clock that drives the daily activities of all living things,<br>\nfrom wild flowers to whales, is wound by Earth\u2019s rotation. The 24-hour<br>\ncycle, tied to one turn of the planet on its axis, embodies a biological<br>\nclock mimicked by timepieces invented to measure the human day.<\/p>\n"],"rendered":"\n<p>The internal clock that drives the daily activities of all living things,<br>\nfrom wild flowers to whales, is wound by Earth\u2019s rotation. The 24-hour<br>\ncycle, tied to one turn of the planet on its axis, embodies a biological<br>\nclock mimicked by timepieces invented to measure the human day.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"But these external clocks don\u2019t exactly match the biological<br>\ntickings inside ourselves. Many measurements led to the conclusion that the<br>\ninternal clock period is actually closer to 25 hours; that is, the biological<br>\nclock was thought to drift toward a 25-hour day unless it is set back an hour<br>\neach day by exposure to morning light and to external clocks. This situation is<br>\nblamed for a long list of sleep problems.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>But these external clocks don\u2019t exactly match the biological<br>\ntickings inside ourselves. Many measurements led to the conclusion that the<br>\ninternal clock period is actually closer to 25 hours; that is, the biological<br>\nclock was thought to drift toward a 25-hour day unless it is set back an hour<br>\neach day by exposure to morning light and to external clocks. This situation is<br>\nblamed for a long list of sleep problems.<\/p>\n","innerContent":["\n<p>But these external clocks don\u2019t exactly match the biological<br>\ntickings inside ourselves. Many measurements led to the conclusion that the<br>\ninternal clock period is actually closer to 25 hours; that is, the biological<br>\nclock was thought to drift toward a 25-hour day unless it is set back an hour<br>\neach day by exposure to morning light and to external clocks. This situation is<br>\nblamed for a long list of sleep problems.<\/p>\n"],"rendered":"\n<p>But these external clocks don\u2019t exactly match the biological<br>\ntickings inside ourselves. Many measurements led to the conclusion that the<br>\ninternal clock period is actually closer to 25 hours; that is, the biological<br>\nclock was thought to drift toward a 25-hour day unless it is set back an hour<br>\neach day by exposure to morning light and to external clocks. This situation is<br>\nblamed for a long list of sleep problems.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Now, the most accurate measurements to date, made by researchers at<br>\nHarvard University, reveal that our natural daily rhythm is much closer to that<br>\nof other living things than previously believed. The better match opens the way<br>\nfor experts to more effectively treat sleep problems involving night work, jet<br>\nlag, Earth-orbiting astronauts, or just not being able to go to sleep and wake<br>\nup on time.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Now, the most accurate measurements to date, made by researchers at<br>\nHarvard University, reveal that our natural daily rhythm is much closer to that<br>\nof other living things than previously believed. The better match opens the way<br>\nfor experts to more effectively treat sleep problems involving night work, jet<br>\nlag, Earth-orbiting astronauts, or just not being able to go to sleep and wake<br>\nup on time.<\/p>\n","innerContent":["\n<p>Now, the most accurate measurements to date, made by researchers at<br>\nHarvard University, reveal that our natural daily rhythm is much closer to that<br>\nof other living things than previously believed. The better match opens the way<br>\nfor experts to more effectively treat sleep problems involving night work, jet<br>\nlag, Earth-orbiting astronauts, or just not being able to go to sleep and wake<br>\nup on time.<\/p>\n"],"rendered":"\n<p>Now, the most accurate measurements to date, made by researchers at<br>\nHarvard University, reveal that our natural daily rhythm is much closer to that<br>\nof other living things than previously believed. The better match opens the way<br>\nfor experts to more effectively treat sleep problems involving night work, jet<br>\nlag, Earth-orbiting astronauts, or just not being able to go to sleep and wake<br>\nup on time.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"By recording the daily rhythms of hormones and body temperatures in 24<br>\nhealthy young and old men and women over a one-month period, the researchers<br>\nconclude that our internal clocks run on a daily cycle of 24 hours, 11<br>\nminutes.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>By recording the daily rhythms of hormones and body temperatures in 24<br>\nhealthy young and old men and women over a one-month period, the researchers<br>\nconclude that our internal clocks run on a daily cycle of 24 hours, 11<br>\nminutes.<\/p>\n","innerContent":["\n<p>By recording the daily rhythms of hormones and body temperatures in 24<br>\nhealthy young and old men and women over a one-month period, the researchers<br>\nconclude that our internal clocks run on a daily cycle of 24 hours, 11<br>\nminutes.<\/p>\n"],"rendered":"\n<p>By recording the daily rhythms of hormones and body temperatures in 24<br>\nhealthy young and old men and women over a one-month period, the researchers<br>\nconclude that our internal clocks run on a daily cycle of 24 hours, 11<br>\nminutes.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"\"That\u2019s slightly longer than 24 hours, but significantly<br>\nshorter than past estimates of 25 hours,\" says Charles Czeisler, professor<br>\nof medicine at the Harvard Medical School. \"Researchers previously reported<br>\na range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation<br>\nbetween our subjects, with a 95 percent level of confidence, was no more than<br>\nplus or minus 16 minutes, a remarkably small range.\"","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>\"That\u2019s slightly longer than 24 hours, but significantly<br>\nshorter than past estimates of 25 hours,\" says Charles Czeisler, professor<br>\nof medicine at the Harvard Medical School. \"Researchers previously reported<br>\na range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation<br>\nbetween our subjects, with a 95 percent level of confidence, was no more than<br>\nplus or minus 16 minutes, a remarkably small range.\"<\/p>\n","innerContent":["\n<p>\"That\u2019s slightly longer than 24 hours, but significantly<br>\nshorter than past estimates of 25 hours,\" says Charles Czeisler, professor<br>\nof medicine at the Harvard Medical School. \"Researchers previously reported<br>\na range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation<br>\nbetween our subjects, with a 95 percent level of confidence, was no more than<br>\nplus or minus 16 minutes, a remarkably small range.\"<\/p>\n"],"rendered":"\n<p>\"That\u2019s slightly longer than 24 hours, but significantly<br>\nshorter than past estimates of 25 hours,\" says Charles Czeisler, professor<br>\nof medicine at the Harvard Medical School. \"Researchers previously reported<br>\na range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation<br>\nbetween our subjects, with a 95 percent level of confidence, was no more than<br>\nplus or minus 16 minutes, a remarkably small range.\"<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"\"These data reveal that the human circadian pacemaker is as stable<br>\nand precise in measuring time as that of other mammals,\" notes Richard<br>\nKronauer, Gordon McKay Professor of Mechanical Engineering. \"These results<br>\napply to both young and older people, and have practical implications for<br>\nunderstanding and developing treatments for sleep disorders tied to circadian<br>\n[daily] rhythms.\"","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>\"These data reveal that the human circadian pacemaker is as stable<br>\nand precise in measuring time as that of other mammals,\" notes Richard<br>\nKronauer, Gordon McKay Professor of Mechanical Engineering. \"These results<br>\napply to both young and older people, and have practical implications for<br>\nunderstanding and developing treatments for sleep disorders tied to circadian<br>\n[daily] rhythms.\"<\/p>\n","innerContent":["\n<p>\"These data reveal that the human circadian pacemaker is as stable<br>\nand precise in measuring time as that of other mammals,\" notes Richard<br>\nKronauer, Gordon McKay Professor of Mechanical Engineering. \"These results<br>\napply to both young and older people, and have practical implications for<br>\nunderstanding and developing treatments for sleep disorders tied to circadian<br>\n[daily] rhythms.\"<\/p>\n"],"rendered":"\n<p>\"These data reveal that the human circadian pacemaker is as stable<br>\nand precise in measuring time as that of other mammals,\" notes Richard<br>\nKronauer, Gordon McKay Professor of Mechanical Engineering. \"These results<br>\napply to both young and older people, and have practical implications for<br>\nunderstanding and developing treatments for sleep disorders tied to circadian<br>\n[daily] rhythms.\"<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Czeisler, Kronauer, and colleagues reported their findings in the June 25<br>\nissue of <i>Science<\/i> magazine. Co-authors of the report include Emery Brown,<br>\nassistant professor of anesthesia; Derk-Jan Dijk, assistant professor of<br>\nmedicine, and research fellow Jeanne Duffy, all of the Harvard Medical<br>\nSchool.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Czeisler, Kronauer, and colleagues reported their findings in the June 25<br>\nissue of <i>Science<\/i> magazine. Co-authors of the report include Emery Brown,<br>\nassistant professor of anesthesia; Derk-Jan Dijk, assistant professor of<br>\nmedicine, and research fellow Jeanne Duffy, all of the Harvard Medical<br>\nSchool.<\/p>\n","innerContent":["\n<p>Czeisler, Kronauer, and colleagues reported their findings in the June 25<br>\nissue of <i>Science<\/i> magazine. Co-authors of the report include Emery Brown,<br>\nassistant professor of anesthesia; Derk-Jan Dijk, assistant professor of<br>\nmedicine, and research fellow Jeanne Duffy, all of the Harvard Medical<br>\nSchool.<\/p>\n"],"rendered":"\n<p>Czeisler, Kronauer, and colleagues reported their findings in the June 25<br>\nissue of <i>Science<\/i> magazine. Co-authors of the report include Emery Brown,<br>\nassistant professor of anesthesia; Derk-Jan Dijk, assistant professor of<br>\nmedicine, and research fellow Jeanne Duffy, all of the Harvard Medical<br>\nSchool.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"<strong>28-Hour Days<\/strong>","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p><strong>28-Hour Days<\/strong><\/p>\n","innerContent":["\n<p><strong>28-Hour Days<\/strong><\/p>\n"],"rendered":"\n<p><strong>28-Hour Days<\/strong><\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"\"It was both surprising and reassuring that the human clock runs<br>\nwith the same precision as that of other living things,\" Czeisler comments.<br>\n\"But we did not expect to find that both young and old people have the same<br>\ndaily period.\"","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>\"It was both surprising and reassuring that the human clock runs<br>\nwith the same precision as that of other living things,\" Czeisler comments.<br>\n\"But we did not expect to find that both young and old people have the same<br>\ndaily period.\"<\/p>\n","innerContent":["\n<p>\"It was both surprising and reassuring that the human clock runs<br>\nwith the same precision as that of other living things,\" Czeisler comments.<br>\n\"But we did not expect to find that both young and old people have the same<br>\ndaily period.\"<\/p>\n"],"rendered":"\n<p>\"It was both surprising and reassuring that the human clock runs<br>\nwith the same precision as that of other living things,\" Czeisler comments.<br>\n\"But we did not expect to find that both young and old people have the same<br>\ndaily period.\"<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Many experts believe that the clock speeds up with age, and they use that<br>\nidea to explain why elders wake up earlier in the morning. With that idea now<br>\nput to bed, researchers need to come up with new theories for these early<br>\nawakenings.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Many experts believe that the clock speeds up with age, and they use that<br>\nidea to explain why elders wake up earlier in the morning. With that idea now<br>\nput to bed, researchers need to come up with new theories for these early<br>\nawakenings.<\/p>\n","innerContent":["\n<p>Many experts believe that the clock speeds up with age, and they use that<br>\nidea to explain why elders wake up earlier in the morning. With that idea now<br>\nput to bed, researchers need to come up with new theories for these early<br>\nawakenings.<\/p>\n"],"rendered":"\n<p>Many experts believe that the clock speeds up with age, and they use that<br>\nidea to explain why elders wake up earlier in the morning. With that idea now<br>\nput to bed, researchers need to come up with new theories for these early<br>\nawakenings.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Why are these measurements more accurate than previous ones?","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Why are these measurements more accurate than previous ones?<\/p>\n","innerContent":["\n<p>Why are these measurements more accurate than previous ones?<\/p>\n"],"rendered":"\n<p>Why are these measurements more accurate than previous ones?<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"\"Other investigators used elaborate procedures to shield subjects<br>\nfrom time cues and the outside world,\" answers Czeisler, who is also<br>\ndirector of circadian and sleep disorders medicine at Brigham and Women\u2019s<br>\nHospital in Boston. \"They even coiled copper wire around the rooms in which<br>\npeople were isolated to counteract natural electromagnetic fields. However,<br>\nthese experimenters allowed their subjects to switch on lights when they were<br>\nawake and turn them off when they wanted to sleep. They didn\u2019t think this<br>\nwould have any effect, but switching on electric lights resets the biological<br>\nclock. It\u2019s the same as resetting your watch.\"","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>\"Other investigators used elaborate procedures to shield subjects<br>\nfrom time cues and the outside world,\" answers Czeisler, who is also<br>\ndirector of circadian and sleep disorders medicine at Brigham and Women\u2019s<br>\nHospital in Boston. \"They even coiled copper wire around the rooms in which<br>\npeople were isolated to counteract natural electromagnetic fields. However,<br>\nthese experimenters allowed their subjects to switch on lights when they were<br>\nawake and turn them off when they wanted to sleep. They didn\u2019t think this<br>\nwould have any effect, but switching on electric lights resets the biological<br>\nclock. It\u2019s the same as resetting your watch.\"<\/p>\n","innerContent":["\n<p>\"Other investigators used elaborate procedures to shield subjects<br>\nfrom time cues and the outside world,\" answers Czeisler, who is also<br>\ndirector of circadian and sleep disorders medicine at Brigham and Women\u2019s<br>\nHospital in Boston. \"They even coiled copper wire around the rooms in which<br>\npeople were isolated to counteract natural electromagnetic fields. However,<br>\nthese experimenters allowed their subjects to switch on lights when they were<br>\nawake and turn them off when they wanted to sleep. They didn\u2019t think this<br>\nwould have any effect, but switching on electric lights resets the biological<br>\nclock. It\u2019s the same as resetting your watch.\"<\/p>\n"],"rendered":"\n<p>\"Other investigators used elaborate procedures to shield subjects<br>\nfrom time cues and the outside world,\" answers Czeisler, who is also<br>\ndirector of circadian and sleep disorders medicine at Brigham and Women\u2019s<br>\nHospital in Boston. \"They even coiled copper wire around the rooms in which<br>\npeople were isolated to counteract natural electromagnetic fields. However,<br>\nthese experimenters allowed their subjects to switch on lights when they were<br>\nawake and turn them off when they wanted to sleep. They didn\u2019t think this<br>\nwould have any effect, but switching on electric lights resets the biological<br>\nclock. It\u2019s the same as resetting your watch.\"<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Kronauer calculated that changing ordinary room light in such experiments<br>\ncan shift the apparent circadian cycle by more than 40 minutes.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Kronauer calculated that changing ordinary room light in such experiments<br>\ncan shift the apparent circadian cycle by more than 40 minutes.<\/p>\n","innerContent":["\n<p>Kronauer calculated that changing ordinary room light in such experiments<br>\ncan shift the apparent circadian cycle by more than 40 minutes.<\/p>\n"],"rendered":"\n<p>Kronauer calculated that changing ordinary room light in such experiments<br>\ncan shift the apparent circadian cycle by more than 40 minutes.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"The Harvard team had their subjects go to bed four hours later each day,<br>\neffectively creating a 28-hour day. This strategy disconnected the biological<br>\npacemaker from clock time.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>The Harvard team had their subjects go to bed four hours later each day,<br>\neffectively creating a 28-hour day. This strategy disconnected the biological<br>\npacemaker from clock time.<\/p>\n","innerContent":["\n<p>The Harvard team had their subjects go to bed four hours later each day,<br>\neffectively creating a 28-hour day. This strategy disconnected the biological<br>\npacemaker from clock time.<\/p>\n"],"rendered":"\n<p>The Harvard team had their subjects go to bed four hours later each day,<br>\neffectively creating a 28-hour day. This strategy disconnected the biological<br>\npacemaker from clock time.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"\"The 28-hour cycle distributed light exposure, sleep and<br>\nwakefulness, work and play evenly around the biological clock,\" explains<br>\nCzeisler. \"The men and women did not get light exposure at the same time<br>\neach clock day. Instead, they experienced a six-day week in which light and dark<br>\noccurred at different times each day.\"","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>\"The 28-hour cycle distributed light exposure, sleep and<br>\nwakefulness, work and play evenly around the biological clock,\" explains<br>\nCzeisler. \"The men and women did not get light exposure at the same time<br>\neach clock day. Instead, they experienced a six-day week in which light and dark<br>\noccurred at different times each day.\"<\/p>\n","innerContent":["\n<p>\"The 28-hour cycle distributed light exposure, sleep and<br>\nwakefulness, work and play evenly around the biological clock,\" explains<br>\nCzeisler. \"The men and women did not get light exposure at the same time<br>\neach clock day. Instead, they experienced a six-day week in which light and dark<br>\noccurred at different times each day.\"<\/p>\n"],"rendered":"\n<p>\"The 28-hour cycle distributed light exposure, sleep and<br>\nwakefulness, work and play evenly around the biological clock,\" explains<br>\nCzeisler. \"The men and women did not get light exposure at the same time<br>\neach clock day. Instead, they experienced a six-day week in which light and dark<br>\noccurred at different times each day.\"<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"This altered schedule freed their internal clocks from the sleep-wake<br>\ncycle and allowed them to tick at the natural period. Despite six-day weeks,<br>\ntheir body temperatures and hormone secretions went through seven cycles every<br>\nweek. Sleepiness was tied to a drop in core body temperature and to an increase<br>\nin melatonin, a hormone secreted by the pineal gland and sold over-the-counter<br>\nas a sleeping pill.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>This altered schedule freed their internal clocks from the sleep-wake<br>\ncycle and allowed them to tick at the natural period. Despite six-day weeks,<br>\ntheir body temperatures and hormone secretions went through seven cycles every<br>\nweek. Sleepiness was tied to a drop in core body temperature and to an increase<br>\nin melatonin, a hormone secreted by the pineal gland and sold over-the-counter<br>\nas a sleeping pill.<\/p>\n","innerContent":["\n<p>This altered schedule freed their internal clocks from the sleep-wake<br>\ncycle and allowed them to tick at the natural period. Despite six-day weeks,<br>\ntheir body temperatures and hormone secretions went through seven cycles every<br>\nweek. Sleepiness was tied to a drop in core body temperature and to an increase<br>\nin melatonin, a hormone secreted by the pineal gland and sold over-the-counter<br>\nas a sleeping pill.<\/p>\n"],"rendered":"\n<p>This altered schedule freed their internal clocks from the sleep-wake<br>\ncycle and allowed them to tick at the natural period. Despite six-day weeks,<br>\ntheir body temperatures and hormone secretions went through seven cycles every<br>\nweek. Sleepiness was tied to a drop in core body temperature and to an increase<br>\nin melatonin, a hormone secreted by the pineal gland and sold over-the-counter<br>\nas a sleeping pill.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Czeisler\u2019s crew also measured changes in cortisol, a hormone<br>\ninvolved in metabolism and other basic body functions. Cortisol naturally drops<br>\nto its lowest levels at bedtime and reaches its highest point during early<br>\nwaking hours.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Czeisler\u2019s crew also measured changes in cortisol, a hormone<br>\ninvolved in metabolism and other basic body functions. Cortisol naturally drops<br>\nto its lowest levels at bedtime and reaches its highest point during early<br>\nwaking hours.<\/p>\n","innerContent":["\n<p>Czeisler\u2019s crew also measured changes in cortisol, a hormone<br>\ninvolved in metabolism and other basic body functions. Cortisol naturally drops<br>\nto its lowest levels at bedtime and reaches its highest point during early<br>\nwaking hours.<\/p>\n"],"rendered":"\n<p>Czeisler\u2019s crew also measured changes in cortisol, a hormone<br>\ninvolved in metabolism and other basic body functions. Cortisol naturally drops<br>\nto its lowest levels at bedtime and reaches its highest point during early<br>\nwaking hours.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"The result was clear. No matter when the subjects went to bed or got up,<br>\nand whatever they did while awake, body temperature and hormones rose and fell<br>\non an average cycle of 24 hours and 11 minutes.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>The result was clear. No matter when the subjects went to bed or got up,<br>\nand whatever they did while awake, body temperature and hormones rose and fell<br>\non an average cycle of 24 hours and 11 minutes.<\/p>\n","innerContent":["\n<p>The result was clear. No matter when the subjects went to bed or got up,<br>\nand whatever they did while awake, body temperature and hormones rose and fell<br>\non an average cycle of 24 hours and 11 minutes.<\/p>\n"],"rendered":"\n<p>The result was clear. No matter when the subjects went to bed or got up,<br>\nand whatever they did while awake, body temperature and hormones rose and fell<br>\non an average cycle of 24 hours and 11 minutes.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"What do people do when isolated in a timeless room for a month? Some of<br>\nthem were graduate students, and they worked on various school projects or wrote<br>\ntheir dissertations. Others did oil paintings or busied themselves with jigsaw<br>\npuzzles. One man, a geologist, brought his rock collection and chipped the time<br>\naway with a rock hammer. Yet others read, thought about the world, and enjoyed<br>\nthe phoneless, e-mailless solitude.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>What do people do when isolated in a timeless room for a month? Some of<br>\nthem were graduate students, and they worked on various school projects or wrote<br>\ntheir dissertations. Others did oil paintings or busied themselves with jigsaw<br>\npuzzles. One man, a geologist, brought his rock collection and chipped the time<br>\naway with a rock hammer. Yet others read, thought about the world, and enjoyed<br>\nthe phoneless, e-mailless solitude.<\/p>\n","innerContent":["\n<p>What do people do when isolated in a timeless room for a month? Some of<br>\nthem were graduate students, and they worked on various school projects or wrote<br>\ntheir dissertations. Others did oil paintings or busied themselves with jigsaw<br>\npuzzles. One man, a geologist, brought his rock collection and chipped the time<br>\naway with a rock hammer. Yet others read, thought about the world, and enjoyed<br>\nthe phoneless, e-mailless solitude.<\/p>\n"],"rendered":"\n<p>What do people do when isolated in a timeless room for a month? Some of<br>\nthem were graduate students, and they worked on various school projects or wrote<br>\ntheir dissertations. Others did oil paintings or busied themselves with jigsaw<br>\npuzzles. One man, a geologist, brought his rock collection and chipped the time<br>\naway with a rock hammer. Yet others read, thought about the world, and enjoyed<br>\nthe phoneless, e-mailless solitude.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"<strong>Rethinking Biological Time<\/strong>","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p><strong>Rethinking Biological Time<\/strong><\/p>\n","innerContent":["\n<p><strong>Rethinking Biological Time<\/strong><\/p>\n"],"rendered":"\n<p><strong>Rethinking Biological Time<\/strong><\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Czeisler, Kronauer, and some colleagues first presented the case for<br>\na near-24-hour biological clock in 1989. \"The many years of experiments<br>\ndone since then, including this latest work, makes us confident in the accuracy<br>\nof our measurements,\" Czeisler says.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Czeisler, Kronauer, and some colleagues first presented the case for<br>\na near-24-hour biological clock in 1989. \"The many years of experiments<br>\ndone since then, including this latest work, makes us confident in the accuracy<br>\nof our measurements,\" Czeisler says.<\/p>\n","innerContent":["\n<p>Czeisler, Kronauer, and some colleagues first presented the case for<br>\na near-24-hour biological clock in 1989. \"The many years of experiments<br>\ndone since then, including this latest work, makes us confident in the accuracy<br>\nof our measurements,\" Czeisler says.<\/p>\n"],"rendered":"\n<p>Czeisler, Kronauer, and some colleagues first presented the case for<br>\na near-24-hour biological clock in 1989. \"The many years of experiments<br>\ndone since then, including this latest work, makes us confident in the accuracy<br>\nof our measurements,\" Czeisler says.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"Apparently, Earth\u2019s rotation impresses a 24-hour period on the genes<br>\nof humans and other living things.<b> <\/b>The human clock consists of a cluster<br>\nof nerve cells (the suprachiasmtic nucleus) barely a hundredth of an inch in<br>\nsize, located deep in the brain and connected to the eyes\u2019 optic<br>\nnerves.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>Apparently, Earth\u2019s rotation impresses a 24-hour period on the genes<br>\nof humans and other living things.<b> <\/b>The human clock consists of a cluster<br>\nof nerve cells (the suprachiasmtic nucleus) barely a hundredth of an inch in<br>\nsize, located deep in the brain and connected to the eyes\u2019 optic<br>\nnerves.<\/p>\n","innerContent":["\n<p>Apparently, Earth\u2019s rotation impresses a 24-hour period on the genes<br>\nof humans and other living things.<b> <\/b>The human clock consists of a cluster<br>\nof nerve cells (the suprachiasmtic nucleus) barely a hundredth of an inch in<br>\nsize, located deep in the brain and connected to the eyes\u2019 optic<br>\nnerves.<\/p>\n"],"rendered":"\n<p>Apparently, Earth\u2019s rotation impresses a 24-hour period on the genes<br>\nof humans and other living things.<b> <\/b>The human clock consists of a cluster<br>\nof nerve cells (the suprachiasmtic nucleus) barely a hundredth of an inch in<br>\nsize, located deep in the brain and connected to the eyes\u2019 optic<br>\nnerves.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"\"Accepting the near-24-hour period means that all the ideas about<br>\ndaily human rhythms that we take for granted must be rethought,\" Czeisler<br>\nsays. For example, biological clock lore states that we drift to a later wake-up<br>\nhour on weekends because we fail to reset the 25-hour cycle each morning as we<br>\ngo to work.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>\"Accepting the near-24-hour period means that all the ideas about<br>\ndaily human rhythms that we take for granted must be rethought,\" Czeisler<br>\nsays. For example, biological clock lore states that we drift to a later wake-up<br>\nhour on weekends because we fail to reset the 25-hour cycle each morning as we<br>\ngo to work.<\/p>\n","innerContent":["\n<p>\"Accepting the near-24-hour period means that all the ideas about<br>\ndaily human rhythms that we take for granted must be rethought,\" Czeisler<br>\nsays. For example, biological clock lore states that we drift to a later wake-up<br>\nhour on weekends because we fail to reset the 25-hour cycle each morning as we<br>\ngo to work.<\/p>\n"],"rendered":"\n<p>\"Accepting the near-24-hour period means that all the ideas about<br>\ndaily human rhythms that we take for granted must be rethought,\" Czeisler<br>\nsays. For example, biological clock lore states that we drift to a later wake-up<br>\nhour on weekends because we fail to reset the 25-hour cycle each morning as we<br>\ngo to work.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"\"We\u2019re not drifting,\" Czeisler insists. \"We\u2019re<br>\npushing ourselves to a later time with our exposure to electric lights from<br>\nsunset to bedtime. That resets our biological clocks.\"","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>\"We\u2019re not drifting,\" Czeisler insists. \"We\u2019re<br>\npushing ourselves to a later time with our exposure to electric lights from<br>\nsunset to bedtime. That resets our biological clocks.\"<\/p>\n","innerContent":["\n<p>\"We\u2019re not drifting,\" Czeisler insists. \"We\u2019re<br>\npushing ourselves to a later time with our exposure to electric lights from<br>\nsunset to bedtime. That resets our biological clocks.\"<\/p>\n"],"rendered":"\n<p>\"We\u2019re not drifting,\" Czeisler insists. \"We\u2019re<br>\npushing ourselves to a later time with our exposure to electric lights from<br>\nsunset to bedtime. That resets our biological clocks.\"<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"The resetting, which leads to difficulty in awakening on Monday, can, in<br>\nmany cases, be \"cured\" by going to bed earlier on weekends. Awakening<br>\ntoo early often can be avoided by going to bed later.","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>The resetting, which leads to difficulty in awakening on Monday, can, in<br>\nmany cases, be \"cured\" by going to bed earlier on weekends. Awakening<br>\ntoo early often can be avoided by going to bed later.<\/p>\n","innerContent":["\n<p>The resetting, which leads to difficulty in awakening on Monday, can, in<br>\nmany cases, be \"cured\" by going to bed earlier on weekends. Awakening<br>\ntoo early often can be avoided by going to bed later.<\/p>\n"],"rendered":"\n<p>The resetting, which leads to difficulty in awakening on Monday, can, in<br>\nmany cases, be \"cured\" by going to bed earlier on weekends. Awakening<br>\ntoo early often can be avoided by going to bed later.<\/p>\n"},{"blockName":"core\/paragraph","attrs":{"align":"","content":"To deal with night-shift work, jet lag, sleeping in an orbiting<br>\nspacecraft, or the winter blues, our biological clocks can be reset by timed<br>\nexposure to bright light. \"To determine the correct exposure, however, we<br>\nmust pin down the internal circadian period, the natural rhythm of our<br>\nbodies,\" Czeisler points out. \"Now, we are able to do this more<br>\neffectively than before.\"","dropCap":false,"placeholder":"","direction":"","lock":[],"metadata":[],"className":"","style":[],"backgroundColor":"","textColor":"","gradient":"","fontSize":"","fontFamily":"","borderColor":"","anchor":""},"innerBlocks":[],"innerHTML":"\n<p>To deal with night-shift work, jet lag, sleeping in an orbiting<br>\nspacecraft, or the winter blues, our biological clocks can be reset by timed<br>\nexposure to bright light. \"To determine the correct exposure, however, we<br>\nmust pin down the internal circadian period, the natural rhythm of our<br>\nbodies,\" Czeisler points out. \"Now, we are able to do this more<br>\neffectively than before.\"<\/p>\n","innerContent":["\n<p>To deal with night-shift work, jet lag, sleeping in an orbiting<br>\nspacecraft, or the winter blues, our biological clocks can be reset by timed<br>\nexposure to bright light. \"To determine the correct exposure, however, we<br>\nmust pin down the internal circadian period, the natural rhythm of our<br>\nbodies,\" Czeisler points out. \"Now, we are able to do this more<br>\neffectively than before.\"<\/p>\n"],"rendered":"\n<p>To deal with night-shift work, jet lag, sleeping in an orbiting<br>\nspacecraft, or the winter blues, our biological clocks can be reset by timed<br>\nexposure to bright light. \"To determine the correct exposure, however, we<br>\nmust pin down the internal circadian period, the natural rhythm of our<br>\nbodies,\" Czeisler points out. \"Now, we are able to do this more<br>\neffectively than before.\"<\/p>\n"}],"innerHTML":"\n<div class=\"wp-block-group alignwide\">\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n<\/div>\n","innerContent":["\n<div class=\"wp-block-group alignwide\">","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","\n\n","<\/div>\n"],"rendered":"\n<div class=\"wp-block-group alignwide has-global-padding is-content-justification-center is-layout-constrained wp-block-group-is-layout-constrained\">\n<figure class=\"wp-block-image alignright size-full is-resized\"><img src=\"https:\/\/news.harvard.edu\/gazette\/wp-content\/uploads\/2016\/09\/bioclock.jpg\" alt=\"\" class=\"wp-image-206411\"\/><figcaption class=\"wp-element-caption\">A. Czeisler and his colleagues have made the most accurate measurements to date of human daily rhythms.\t\t\t<\/figcaption><\/figure>\n\n\n\n<p>The internal clock that drives the daily activities of all living things,<br>\nfrom wild flowers to whales, is wound by Earth\u2019s rotation. The 24-hour<br>\ncycle, tied to one turn of the planet on its axis, embodies a biological<br>\nclock mimicked by timepieces invented to measure the human day.<\/p>\n\n\n\n<p>But these external clocks don\u2019t exactly match the biological<br>\ntickings inside ourselves. Many measurements led to the conclusion that the<br>\ninternal clock period is actually closer to 25 hours; that is, the biological<br>\nclock was thought to drift toward a 25-hour day unless it is set back an hour<br>\neach day by exposure to morning light and to external clocks. This situation is<br>\nblamed for a long list of sleep problems.<\/p>\n\n\n\n<p>Now, the most accurate measurements to date, made by researchers at<br>\nHarvard University, reveal that our natural daily rhythm is much closer to that<br>\nof other living things than previously believed. The better match opens the way<br>\nfor experts to more effectively treat sleep problems involving night work, jet<br>\nlag, Earth-orbiting astronauts, or just not being able to go to sleep and wake<br>\nup on time.<\/p>\n\n\n\n<p>By recording the daily rhythms of hormones and body temperatures in 24<br>\nhealthy young and old men and women over a one-month period, the researchers<br>\nconclude that our internal clocks run on a daily cycle of 24 hours, 11<br>\nminutes.<\/p>\n\n\n\n<p>\"That\u2019s slightly longer than 24 hours, but significantly<br>\nshorter than past estimates of 25 hours,\" says Charles Czeisler, professor<br>\nof medicine at the Harvard Medical School. \"Researchers previously reported<br>\na range of 13 to 65 hours, with a median of 25 hours, 12 minutes. The variation<br>\nbetween our subjects, with a 95 percent level of confidence, was no more than<br>\nplus or minus 16 minutes, a remarkably small range.\"<\/p>\n\n\n\n<p>\"These data reveal that the human circadian pacemaker is as stable<br>\nand precise in measuring time as that of other mammals,\" notes Richard<br>\nKronauer, Gordon McKay Professor of Mechanical Engineering. \"These results<br>\napply to both young and older people, and have practical implications for<br>\nunderstanding and developing treatments for sleep disorders tied to circadian<br>\n[daily] rhythms.\"<\/p>\n\n\n\n<p>Czeisler, Kronauer, and colleagues reported their findings in the June 25<br>\nissue of <i>Science<\/i> magazine. Co-authors of the report include Emery Brown,<br>\nassistant professor of anesthesia; Derk-Jan Dijk, assistant professor of<br>\nmedicine, and research fellow Jeanne Duffy, all of the Harvard Medical<br>\nSchool.<\/p>\n\n\n\n<p><strong>28-Hour Days<\/strong><\/p>\n\n\n\n<p>\"It was both surprising and reassuring that the human clock runs<br>\nwith the same precision as that of other living things,\" Czeisler comments.<br>\n\"But we did not expect to find that both young and old people have the same<br>\ndaily period.\"<\/p>\n\n\n\n<p>Many experts believe that the clock speeds up with age, and they use that<br>\nidea to explain why elders wake up earlier in the morning. With that idea now<br>\nput to bed, researchers need to come up with new theories for these early<br>\nawakenings.<\/p>\n\n\n\n<p>Why are these measurements more accurate than previous ones?<\/p>\n\n\n\n<p>\"Other investigators used elaborate procedures to shield subjects<br>\nfrom time cues and the outside world,\" answers Czeisler, who is also<br>\ndirector of circadian and sleep disorders medicine at Brigham and Women\u2019s<br>\nHospital in Boston. \"They even coiled copper wire around the rooms in which<br>\npeople were isolated to counteract natural electromagnetic fields. However,<br>\nthese experimenters allowed their subjects to switch on lights when they were<br>\nawake and turn them off when they wanted to sleep. They didn\u2019t think this<br>\nwould have any effect, but switching on electric lights resets the biological<br>\nclock. It\u2019s the same as resetting your watch.\"<\/p>\n\n\n\n<p>Kronauer calculated that changing ordinary room light in such experiments<br>\ncan shift the apparent circadian cycle by more than 40 minutes.<\/p>\n\n\n\n<p>The Harvard team had their subjects go to bed four hours later each day,<br>\neffectively creating a 28-hour day. This strategy disconnected the biological<br>\npacemaker from clock time.<\/p>\n\n\n\n<p>\"The 28-hour cycle distributed light exposure, sleep and<br>\nwakefulness, work and play evenly around the biological clock,\" explains<br>\nCzeisler. \"The men and women did not get light exposure at the same time<br>\neach clock day. Instead, they experienced a six-day week in which light and dark<br>\noccurred at different times each day.\"<\/p>\n\n\n\n<p>This altered schedule freed their internal clocks from the sleep-wake<br>\ncycle and allowed them to tick at the natural period. Despite six-day weeks,<br>\ntheir body temperatures and hormone secretions went through seven cycles every<br>\nweek. Sleepiness was tied to a drop in core body temperature and to an increase<br>\nin melatonin, a hormone secreted by the pineal gland and sold over-the-counter<br>\nas a sleeping pill.<\/p>\n\n\n\n<p>Czeisler\u2019s crew also measured changes in cortisol, a hormone<br>\ninvolved in metabolism and other basic body functions. Cortisol naturally drops<br>\nto its lowest levels at bedtime and reaches its highest point during early<br>\nwaking hours.<\/p>\n\n\n\n<p>The result was clear. No matter when the subjects went to bed or got up,<br>\nand whatever they did while awake, body temperature and hormones rose and fell<br>\non an average cycle of 24 hours and 11 minutes.<\/p>\n\n\n\n<p>What do people do when isolated in a timeless room for a month? Some of<br>\nthem were graduate students, and they worked on various school projects or wrote<br>\ntheir dissertations. Others did oil paintings or busied themselves with jigsaw<br>\npuzzles. One man, a geologist, brought his rock collection and chipped the time<br>\naway with a rock hammer. Yet others read, thought about the world, and enjoyed<br>\nthe phoneless, e-mailless solitude.<\/p>\n\n\n\n<p><strong>Rethinking Biological Time<\/strong><\/p>\n\n\n\n<p>Czeisler, Kronauer, and some colleagues first presented the case for<br>\na near-24-hour biological clock in 1989. \"The many years of experiments<br>\ndone since then, including this latest work, makes us confident in the accuracy<br>\nof our measurements,\" Czeisler says.<\/p>\n\n\n\n<p>Apparently, Earth\u2019s rotation impresses a 24-hour period on the genes<br>\nof humans and other living things.<b> <\/b>The human clock consists of a cluster<br>\nof nerve cells (the suprachiasmtic nucleus) barely a hundredth of an inch in<br>\nsize, located deep in the brain and connected to the eyes\u2019 optic<br>\nnerves.<\/p>\n\n\n\n<p>\"Accepting the near-24-hour period means that all the ideas about<br>\ndaily human rhythms that we take for granted must be rethought,\" Czeisler<br>\nsays. For example, biological clock lore states that we drift to a later wake-up<br>\nhour on weekends because we fail to reset the 25-hour cycle each morning as we<br>\ngo to work.<\/p>\n\n\n\n<p>\"We\u2019re not drifting,\" Czeisler insists. \"We\u2019re<br>\npushing ourselves to a later time with our exposure to electric lights from<br>\nsunset to bedtime. That resets our biological clocks.\"<\/p>\n\n\n\n<p>The resetting, which leads to difficulty in awakening on Monday, can, in<br>\nmany cases, be \"cured\" by going to bed earlier on weekends. Awakening<br>\ntoo early often can be avoided by going to bed later.<\/p>\n\n\n\n<p>To deal with night-shift work, jet lag, sleeping in an orbiting<br>\nspacecraft, or the winter blues, our biological clocks can be reset by timed<br>\nexposure to bright light. \"To determine the correct exposure, however, we<br>\nmust pin down the internal circadian period, the natural rhythm of our<br>\nbodies,\" Czeisler points out. \"Now, we are able to do this more<br>\neffectively than before.\"<\/p>\n<\/div>\n"}},"jetpack-related-posts":[{"id":207029,"url":"https:\/\/news.harvard.edu\/gazette\/story\/2003\/09\/when-light-has-you-singing-the-blues\/","url_meta":{"origin":206410,"position":0},"title":"When light has you singing the blues:","author":"gazetteimport","date":"September 25, 2003","format":false,"excerpt":"Blue light outshone white in a Harvard University experiment to find better ways to reset our body clocks.","rel":"","context":"In "Campus & Community"","block_context":{"text":"Campus & Community","link":"https:\/\/news.harvard.edu\/gazette\/section\/campus-community\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":219122,"url":"https:\/\/news.harvard.edu\/gazette\/story\/2000\/05\/biological-clock-genes-identified-2\/","url_meta":{"origin":206410,"position":1},"title":"Biological clock genes identified","author":"gazetteimport","date":"May 25, 2000","format":false,"excerpt":"Steve Reppert's 25-year-old son, a sculptor, made the mechanism pictured which helps Reppert describe his discoveries about how the natural clock in our heads work. Staff photo by Rose Lincoln Scientists have gotten the closest look yet at the inner works of biological clocks that drive our natural sleep-wake cycle.\u2026","rel":"","context":"In "Campus & Community"","block_context":{"text":"Campus & Community","link":"https:\/\/news.harvard.edu\/gazette\/section\/campus-community\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":219455,"url":"https:\/\/news.harvard.edu\/gazette\/story\/2002\/01\/at-hms-learning-how-body-clock-sets-itself\/","url_meta":{"origin":206410,"position":2},"title":"At HMS: Learning how body clock sets itself","author":"gazetteimport","date":"January 17, 2002","format":false,"excerpt":"Harvard Medical School (HMS) researchers have gained one of the first glimpses of how the bodys circadian clock - a tiny cluster of nerve cells behind the eyes - sends out the signals that control natural daily rhythms. The newly discovered pathway, reported in the Dec. 21 edition of Science,\u2026","rel":"","context":"In "Campus & Community"","block_context":{"text":"Campus & Community","link":"https:\/\/news.harvard.edu\/gazette\/section\/campus-community\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":297525,"url":"https:\/\/news.harvard.edu\/gazette\/story\/2020\/03\/harvards-keeper-of-historic-and-antique-clocks\/","url_meta":{"origin":206410,"position":3},"title":"A faithful keeper of time","author":"Lian Parsons","date":"March 5, 2020","format":false,"excerpt":"Harvard\u2019s on-call horologist Richard Ketchen keeps busy round the clock.","rel":"","context":"In "Campus & Community"","block_context":{"text":"Campus & Community","link":"https:\/\/news.harvard.edu\/gazette\/section\/campus-community\/"},"img":{"alt_text":"Richard Ketchen working on a clock.","src":"https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/02\/021420_Ketchen_Richard_139_2500.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/02\/021420_Ketchen_Richard_139_2500.jpg?resize=350%2C200 1x, https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/02\/021420_Ketchen_Richard_139_2500.jpg?resize=525%2C300 1.5x, https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/02\/021420_Ketchen_Richard_139_2500.jpg?resize=700%2C400 2x"},"classes":[]},{"id":295328,"url":"https:\/\/news.harvard.edu\/gazette\/story\/2020\/01\/researchers-unveil-stem-cell-models-of-human-spine-development\/","url_meta":{"origin":206410,"position":4},"title":"Backbone of success","author":"harvardgazette","date":"January 8, 2020","format":false,"excerpt":"Harvard researchers have unveiled the first stem cell models of human spine development, setting the stage for better understanding of musculoskeletal and metabolic disorders, including congenital scoliosis, muscular dystrophy, and Type 2 diabetes.","rel":"","context":"In "Science & Tech"","block_context":{"text":"Science & Tech","link":"https:\/\/news.harvard.edu\/gazette\/section\/science-technology\/"},"img":{"alt_text":"Engraving of a spine.","src":"https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/01\/iStock-165651993.jpg?resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/01\/iStock-165651993.jpg?resize=350%2C200 1x, https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/01\/iStock-165651993.jpg?resize=525%2C300 1.5x, https:\/\/news.harvard.edu\/wp-content\/uploads\/2020\/01\/iStock-165651993.jpg?resize=700%2C400 2x"},"classes":[]},{"id":3595,"url":"https:\/\/news.harvard.edu\/gazette\/story\/2008\/05\/study-identifies-food-related-clock-in-brain\/","url_meta":{"origin":206410,"position":5},"title":"Study identifies food-related clock in brain","author":"harvardgazette","date":"May 29, 2008","format":false,"excerpt":"n investigating the intricacies of the body\u2019s biological rhythms, scientists at Beth Israel Deaconess Medical Center (BIDMC) have discovered the existence of a \u201cfood-related clock,\u201d which can supersede the \u201clight-based\u201d master clock that serves as the body\u2019s primary timekeeper.","rel":"","context":"In "Health"","block_context":{"text":"Health","link":"https:\/\/news.harvard.edu\/gazette\/section\/health\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/posts\/206410","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/users\/108097152"}],"replies":[{"embeddable":true,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/comments?post=206410"}],"version-history":[{"count":2,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/posts\/206410\/revisions"}],"predecessor-version":[{"id":376783,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/posts\/206410\/revisions\/376783"}],"wp:attachment":[{"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/media?parent=206410"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/categories?post=206410"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/tags?post=206410"},{"taxonomy":"format","embeddable":true,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/gazette-formats?post=206410"},{"taxonomy":"series","embeddable":true,"href":"https:\/\/news.harvard.edu\/gazette\/wp-json\/wp\/v2\/series?post=206410"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}