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Coffee Jitters: Caffeine boosts predictor of heart problems

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7:34am, December 26, 2002
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Whether it comes from coffee or another source, caffeine gives a troubling boost to one biological indicator of poor heart health, a new study suggests. Moreover, other ingredients in coffee appear to at least double the effect of caffeine alone.

Past studies have shown that drinking coffee can increase blood concentrations of the amino acid homocysteine, which has been associated with an elevated risk of heart attacks (SN: 1/11/97, p. 22). Meanwhile, quitting coffee can reduce blood concentrations of both homocysteine and artery-damaging cholesterol (SN: 9/22/01, p. 180: Even a little coffee may up heart risk).

Petra Verhoef of Wageningen University in the Netherlands and her colleagues set out to test whether caffeine is responsible for coffee's homocysteine-raising effect. For each 11-day study period, the researchers gave volunteers one of three daily treatments: 0.9 liters of filtered coffee, six pills containing an equivalent amount of caffeine, or six caffeinefree pills. During the trial, every volunteer received a course of each treatment and was asked to refrain from consuming other items that contain caffeine.

Twice during each treatment period, the researchers collected blood samples from the volunteers before and after they ate breakfast and consumed half their daily coffee or pills. People who weren't consuming caffeine had an average prebreakfast homocysteine concentration of 9.6 micromoles per liter (mol/l), compared with 10.0 mol/l for volunteers taking caffeine pills and 10.5 mol/l for people on the coffee treatment. Although these differences are small, they indicate statistically significant rises in homocysteine during treatments featuring caffeine, Verhoef and her team report in the December 2002 American Journal of Clinical Nutrition.

In general, volunteers' homocysteine concentrations fell nearly 1 mol/l after breakfast, even when caffeine pills were part of the meal. However, drinking coffee with breakfast canceled the meal's usual homocysteine-lowering effect.

The study confirms researchers' suspicion that caffeine contributes to coffee's homocysteine-raising effect, says Paul F. Jacques of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. It also indicates that caffeine isn't responsible for the entire effect, he says.

Given the modest homocysteine increases shown in the new study, it shouldn't cause much concern for coffee drinkers, says Stein Emil Vollset of the University of Bergen in Norway.

In a separate new nationwide study of health data on 7,103 people, investigators correlated an increase in blood homocysteine with a rise in blood pressure and risk of heart and artery problems. Women with the highest homocysteine concentrations were three times as likely to have hypertension as were women whose concentrations measured about 5 mol/l lower. Men showed a smaller correlation, Unhee Lim and Patricia A. Cassano of Cornell University report in the Dec. 15, 2002 American Journal of Epidemiology.

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