Researchers at Harvard-affiliated Brigham and Women’s Hospital (BWH) have found that both long and short sleep durations may be independently associated with an increased risk of heart disease in women. These findings are published in the Jan. 27 issue of the Archives of Internal Medicine.
“There have been several studies examining the impact of short duration sleep deprivation,” said Najib Ayas, of BWH. “However, our research is one of the first to hypothesize that sustained reduced sleep duration as well as an excess could negatively impact a woman’s cardiovascular health. Our data reflect that short and long sleepers may be at a higher risk of coronary heart disease (CHD).”
Ayas, who is an instructor in medicine at Harvard Medical School, and his team found that sleeping five hours or less per night was associated with a 30 percent increase in risk of CHD, and sleeping six hours per night was associated with an 18 percent greater risk. Women who slept eight hours per night had the lowest recorded rate of CHD.
Chronic sleep deprivation is common in today’s society. It is reported that a third of Americans sleep six hours per day or less. Previous research has shown that the effects of short-term reduced sleep duration include increased blood pressure, heart-rate variability, decreased glucose tolerance, and increased cortisol levels. Yet, little is known about how the duration of sleep impacts long-term health outcomes, such as one’s risk of CHD, the No. 1 killer of both men and women in the United States. CHD, caused by the narrowing of the coronary arteries and a common catalyst for heart attacks, is greatly influenced by a variety of lifestyle choices, such as exercise, smoking, and diet. BWH researchers have now revealed sleep may weigh into that equation, too.
In a 10-year period, 934 cases of CHD (myocardial infarction) were reported among 71,617 women participating in the BWH-based Nurses’ Health Study. The women were asked to self-report on their sleeping patterns and a variety of health and lifestyle factors.
“Our study suggests that curtailing sleep may have adverse cardiovascular consequences,” said Ayas. “This research sends an important message to a population that is spending more and more time working and staying up late watching television or using the Internet. Adequate daily sleep should not be considered a luxury, but an important component of a healthy lifestyle.”
Overall, the research establishes an important link between sleep and cardiovascular health, although more research is required to better understand the biological mechanisms underlying this correlation. With prior knowledge about the debilitating influence of short-term sleep deprivation, the association revealed between chronic sleep deprivation and increased risk of CHD was consistent with research team’s original hypothesis. However, unexpectedly, the data also showed that increased sleep duration – nine or more hours of sleep – was also associated with an increased risk of CHD. In this study, among the 5 percent of women who slept on average nine to 11 hours, there were 59 reported cases of CHD. These women were 38 percent more likely to suffer from CHD than women who slept eight hours a night. The reason for the positive relationship between increased sleep duration and CHD remains elusive at the present time.
“While further investigation will pinpoint the causes, we now know that the quantity of sleep women are getting – whether it is too much or too little – seems to be an important factor in maintaining a healthy heart,” noted Ayas.