Where lies coffee's stimulant?

Last week we reported on a study that suggested the buzz we get from coffee may not, unlike the widely held belief, actually be from caffeine. This week, new research finds that brewed coffee raises homocysteine levels and risk factors for coronary heart disease higher than when compared with the ingestion of caffeine alone.

Researchers in the Netherlands investigating the effects of caffeine alone and in brewed coffee found that brewed coffee increased homocysteine levels in healthy volunteers within hours of consumption and seemed to have a particularly strong effect when taken after meals.

High plasma homocysteine concentration is associated with an increased risk of cardiovascular disease, and both consumption of unfiltered and filtered coffee raises homocysteine levels. However it was unclear which substances in brewed coffee are responsible for its homocysteine-raising properties.

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 per cent of the subjects were smokers, who are known to metabolise 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 per cent after the subjects drank brewed coffee for 2 weeks, compared to a 5 per cent 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.

The researchers noted that epidemiologic associations between coffee consumption and cardiovascular disease are conflicting and therefore, the public health implications of the homocysteine-raising effects of caffeine and coffee would remain unclear until a causal relation between high homocysteine concentrations and heart disease is proven.

The study is published in the December issue of the American Journal of Clinical Nutrition​.