Nov. 8, 2005 - Women who drink lots of coffee can relax. But those who drink lots of cola may have a problem: high blood pressure.
High blood pressure isn't good. It's linked to heart disease and stroke. There's been a lot of worry that everyday coffee drinkers may be at increased risk of high blood pressure.
But that doesn't seem to be the case. Recent studies found little risk among coffee-swilling men. Now data from the two large Nurses Health studies -- which followed some 155,000 women for 12 years -- show that heavy coffee drinkers don't risk developing high blood pressure.
There was, however, an entirely unexpected finding. Women who drank just one caffeinated cola drink every day had a slightly higher risk of high blood pressure. And that risk went up as women drank more daily colas, says researcher Wolfgang C. Winkelmayer, MD, ScD, of Brigham and Women's Hospital and Harvard University in Boston.
"We did find an association between consumption of cola beverages, whether regular or diet, and increased risk of high blood pressure," Winkelmayer tells WebMD. "No previous studies suggested such an association. But the finding was consistent, both for younger and older women. We were very surprised."
Colas in the study included Coke, Pepsi, and other dark-colored sodas.
Winkelmayer and colleagues report their findings in the Nov. 9 issue of The Journal of the American Medical Association.
The study shows a strong link between high blood pressure and caffeinated cola consumption. But it doesn't prove cola drinks cause high blood pressure.
Even so, cola drinking remained a risk factor even when the researchers compared only women matched for age, weight, alcohol use, previous trouble with high blood pressure, use of birth control pills, physical activity, smoking, and use of other classes of beverages.
Compared with women who drank less than a can of regular cola a day:
- Women who drank one can of cola a day increased their high blood pressure risk by 9% in the first Nurses Health Study and by 13% in the second Nurses Health Study.
- Women who drank two to three cans of cola a day had an 11% higher risk in the first study and a 24% higher risk in the second study.
- Women who drank four or more cans of cola a day had a 44% higher risk in the first study and a 28% higher risk in the second study.
Compared with women who drank less than a can of diet cola a day:
- Women who drank one can of diet cola a day increased their high blood pressure risk by 7% in the first Nurses Health Study and by 5% in the second Nurses Health Study.
- Women who drank two to three cans of diet cola a day had a 6% higher risk in the first study and a 9% higher risk in the second study.
- Women who drank four or more cans of cola a day had a 16% higher risk in the first study and a 19% higher risk in the second study.
Identifying the Culprit
What's going on? There are ingredients in cola drinks -- corn syrup in sugared colas and caramel coloring in both sugared and diet colas -- that might cause high blood pressure. This is far from proven, Winkelmayer hastens to point out.
"Clearly, at this point, we need to be very careful and require further research to confirm this finding," he says. "If cola drinking is, in fact, a cause of high blood pressure, it would be important to identify the biological mechanism that makes this happen. We need to understand what it is that creates this link. This agent needs to be identified."
Even so, the link between cola and high blood pressure worries Richard Milani, MD, head of preventive cardiology at the Ochsner Clinic Foundation in New Orleans.
"The unexpected and rather alarming finding of this study is this very strong and increasing risk of high blood pressure as women drink more and more cola," Milani tells WebMD. "That is very, very concerning, because of the even larger amount of cola consumption in U.S. children. We don't see 10-year-olds drinking coffee, but we do see 6-year-olds drinking their weight in cola. This is an alarming finding."
Though the findings aren't good news for people shoving quarters into soda machines, they're a relief to those queuing up for coffee.
Short-term studies show that people who drink coffee experience a rise in blood pressure. Doctors worried about what this might mean for people who drank a lot of coffee every day. But research suggests that these short-term effects don't persist in people who are used to drinking coffee every day. The current study shows this, Winkelmayer says.
"The message is particularly a good one for women who really enjoy drinking coffee -- in the morning, in the evening, or in large quantities," he says. "They can be relieved and quite certain that their behavior does not put them at risk for high blood pressure."
That fits with a 2002 study that found only a weak association between coffee consumption and high blood pressure in men. And it also fits with a 2000 study of Danish men and women, finding no increased risk of heart disease or death among coffee drinkers.