The 21 male and 27 female participants in the study, aged 19 to 65 years old, were all heavy coffee drinkers who consumed 6 or more cups of filtered or instant coffee daily. Thirty-one percent of the subjects were smokers, who are known to metabolize caffeine more rapidly than non-smokers. Three treatments, administered in random order for a period of 2 weeks each, consisted of either capsules containing 870mg of caffeine daily; 4 cups of strong filtered coffee that contained 870 mg of caffeine; or placebo capsules. Despite the fact that both treatments had a similar amount of caffeine, the average fasting homocysteine concentration rose by 11% after the subjects drank brewed coffee for 2 weeks, compared to a 5% increase after caffeine alone. The paper filter in the brewed coffee retained trace amounts of several substances that were suspected to be responsible for the rise in homocysteine concentrations, including chlorogenic acid (a polyphenolic compound) that is not removed by filtering.
Epidemiologic associatations between coffee consumption and CVD are conflicting; therefore, public health implications of the homocysteine-raising effects of caffeine and coffee will remain unclear until a causal relation between high homocysteine concentrations and CVD is proven.
Verhoef, Petra et al. Contribution of caffeine to the homocysteine-raising effect of coffee: a randomized controlled trial in humans. Am J Clin Nutr 2002;76:1244-8.
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