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November 10, 2005

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Coffee gets cleared of blood pressure risk

But not caffeinated sodas

By William J. Cromie
Harvard News Office

cup of coffee and glass of soda pop
Women who drink more than three cups of coffee a day are less likely to develop high blood pressure than those who drink four or more cans of caffeinated soda a day. (Staff photo Rose Lincoln/Harvard News Office)
Relax ladies and, possibly, gentlemen. Have that second cup of coffee. The largest study to date concludes that the caffeine won't raise your risk of high blood pressure.

However, too much soda pop, sugared or diet, might.

Harvard researchers set out to test the idea that a lot of coffee isn't good for your circulation. They followed 155,000 female nurses for 12 years, questioning them regularly about their caffeine-drinking habits and their blood pressure. No connection was found between their coffee intake and a risky rise in blood pressure.

In fact, results went the other way. Women who drank the most coffee seemed to develop some protection against the problem. The investigators continue to look into this possibility.

Caffeine may not be the reason, however. The researchers found that things went the other way when women drank copious amount of caffeine-containing colas. Sugared or diet, the soft drinks increased their risk of high blood pressure by as much as 44 percent, compared with those who drank very little soda.

Tea drinking produced mixed results. That beverage increased hypertension risk in younger but not older women. The study did not collect information on that warming winter favorite - hot chocolate.

"Given that coffee and other caffeinated beverages are among the most widely consumed in the world, any detrimental effects of caffeine on health could have enormous public health implications," notes Wolfgang Winkelmayer, an assistant professor of medicine at Harvard Medical School and Harvard-affiliated Brigham and Women's Hospital in Boston. "High blood pressure is a silent, but extremely dangerous disease that impacts at least 50 million people in the United States alone."

And the numbers are increasing. That's the bad news because high blood pressure is a major risk factor for heart disease, stroke, congestive heart failure, and lethal kidney disease. The good news, says Winkelmayer, is that "we can dispel the myth that habitual coffee drinking leads to hypertension in women."

What about men?

Can men also enjoy their daily coffee rituals without fear of upping their risk of heart disease?

"We currently do not know whether these findings also pertain to men," Winkelmayer answers. "The only long-term evidence comes from a recent study of about a thousand men, which found no suggestive association between caffeine intake and an increased risk of hypertension. We are currently investigating this issue. It's a work in progress."

Meanwhile, without any good evidence that they would react differently, men probably shouldn't worry about it.

Winkelmayer worked with colleagues from both Brigham and Women's Hospital and the Harvard School of Public Health on the study. For these researchers, the big surprise was finding a link between consumption of soda and high blood pressure risk.

As they report in the Nov. 9 issue of the Journal of the American Medical Association, older women, ages 43 to 71 at the start of the study, had the biggest risk of developing high blood pressure. Those who gulped four or more cans or glasses of caffeinated sugared cola each day had a 44 percent greater risk of hypertension compared with those who drank less than one a day.

Things were better for younger women, 26 to 46 years old. Those who sipped four or more cans of sugared colas increased their risk 28 percent compared with those who drank less than a can a day.

Things went even better for diet-soda drinkers. The risk for younger women rose 19 percent. The risk for older women increased 16 percent with four or more cans of diet colas.

Since the researchers found no increased risk of danger with either regular or decaffeinated coffee, they speculate that "it is not caffeine but perhaps some other compound contained in soda-type soft drinks that may be responsible for the increased risk of high blood pressure."

"At present, no biological explanation exists for the association between soda and hypertension," Winkelmayer admits, "therefore, no recommendations about soda drinking can be made."

Women concerned about the effects of drinking soda on their health may want to cut back on the fizzy stuff, but those who believe that life would not be as pleasant without several cups of coffee a day can relax and enjoy the popular beverage.

Copyright 2007 by the President and Fellows of Harvard College