Providence, RI - Coffee may trigger MI in sedentary people with other cardiovascular risk factors, particularly if they are not regular coffee drinkers, a new study shows [1]. Writing in the September 2006 issue of Epidemiology, Dr Ana Baylin (Brown University, Providence, RI) and colleagues say that the effect of coffee as a trigger would likely be strongest in the morning, when plasma caffeine levels are typically at their lowest and the circadian pattern of cardiovascular risk is at its peak.

The authors examined 503 incident cases of MI between 1994 and 1998 in Costa Rica, a country where coffee consumption at roughly 325 mg/person/day is similar to the US and many European countries. Information on habitual intake of coffee was derived from a survey conducted within two weeks of hospital discharge. Of the MI patients surveyed, only 37% reported drinking no coffee; most reported drinking two to three cups per day, with men being heavier coffee drinkers than women.

Of the 503 patients surveyed, 80 had at least one cup within the hour before the onset of their myocardial infarction: as such, the relative risk of MI in the hour after coffee consumption was 1.49. When patients were stratified according to usual coffee intake, light and occasional coffee drinkers had a relative risk of MI that was almost four times higher than that of heavy coffee drinkers and more than double that of moderate coffee drinkers.

When cardiovascular risk factors were taken into account, patients with three or more risk factors had a relative risk for MI of 2.10 within one hour of coffee consumption, while patients with fewer than three risk factors had a relative risk of 1.39. Sedentary coffee drinkers also were more likely to have an MI within one hour of coffee consumption as compared with more active patients (relative risk 1.72 vs 1.07).

"The findings indicate that coffee intake may trigger myocardial infarction," Baylin et al conclude. "The association is particularly strong among people with light/occasional intake of coffee (up to a cup/day), those with a sedentary lifestyle, and those with three or more risk factors for coronary heart disease."

Of note, other potential temporal triggers of MI not reported in the paper might have been factors, the authors note: notably concurrent smoking, physical activity, or sexual intercourse in the hour prior to MI.

In a Commentary accompanying the study [2], Dr David Siscovick (University of Washington, Seattle) points out that, like coffee, other exposures such as anger, physical exertion, and air pollution also alter sympathetic activity and have been identified as MI "triggers." Further research is warranted into ways of modifying exposure to triggers or blunting reaction via physical fitness or drugs, Siscovick writes.

"Given the widespread consumption of coffee, these findings need to be put into perspective," he adds, noting that the increase in risk associated with coffee consumption is likely transient and limited to a subset of higher-risk people. "Even among the most susceptible people (the occasional and light coffee drinkers), the transient fourfold increase in MI risk in the hour after coffee intake will result in only a small increase in the absolute risk of MI, given the low absolute risk of MI per hour."

Also commenting on the findings for heartwire, Dr Rune Blomhoff (University of Oslo, Norway), who did not participate in the study, pointed out that other research has suggested that coffee can also have health benefits, potentially due to its antioxidant components. His own group recently demonstrated that consumption of one to three cups of coffee per day was associated with a 25% lower risk of death attributable to cardiovascular disease in postmenopausal women [3].

"Although there may be a transient increased risk of nonfatal myocardial infarction the first hour after intake of coffee, several studies suggest that the overall total effect of coffee consumption seems to be protective with regard to total and cardiovascular death and risk of inflammatory diseases such as Parkinson's disease, gallstones, liver cirrhosis, and diabetes," Blomhoff told heartwire.