Coffee Consumption and Mortality
Abstract & Commentary
By Andrew J. Boyle, MBBS, PhD
Assistant Professor of Medicine, Interventional Cardiology, University of California, San Francisco
Source: Freedman ND, et al. Association of coffee drinking with total and cause-specific mortality. N Engl J Med 2012;366:1891-1904.
Coffee is widely consumed throughout the United States. Some prior studies have associated coffee consumption with increased rates of heart disease, whereas other studies have shown less heart disease in coffee drinkers. The data associating coffee consumption and total mortality have also been conflicting. In the New England Journal of Medicine, Freedman and colleagues examined the association of coffee drinking with subsequent total and cause-specific mortality among 229,119 men and 173,141 women in the National Institutes of Health–AARP Diet and Health Study.
This very large cohort study enrolled subjects (AARP members) who were 50 to 71 years of age, and assessed dietary and lifestyle factors. Coffee consumption was assessed once at baseline. Participants with cancer, heart disease, and stroke were excluded. The subjects were followed for 14 years (5,148,760 person-years of follow-up) and the data were linked to the Social Security Administration Death Master File to assess mortality. In age-adjusted models, the risk of death was increased among coffee drinkers. However, coffee drinkers were also more likely to smoke, and after adjustment for smoking status and other potential confounders, there was a significant inverse association between coffee consumption and mortality. Adjusted hazard ratios for death among men who drank coffee as compared with those who did not were: 0.99 for drinking less than 1 cup per day, 0.94 for 1 cup, 0.90 for 2 or 3 cups, 0.88 for 4 or 5 cups, and 0.90 for 6 or more cups of coffee per day (P < 0.001). The respective hazard ratios among women were 1.01, 0.95, 0.87, 0.84, and 0.85 (P < 0.001). Reduced mortality was observed for deaths due to heart disease, respiratory disease, stroke, injuries and accidents, diabetes, and infections. However, cancer-related deaths were not reduced, and there was a trend toward higher mortality from cancer in men who drank more than 6 cups per day. Interestingly, both caffeinated and decaffeinated coffee were associated with similar reductions in mortality. The authors conclude that coffee consumption was inversely associated with total and cause-specific mortality, but whether this was a causal or associational finding cannot be determined from these data.
This study is welcome news for coffee drinkers. However, several aspects of this study need to be taken into account. First, this was an observational study, and therefore cause and effect cannot be concluded from these data. Second, coffee consumption was ascertained at baseline and never again throughout 14 years of follow-up. Patterns of consumption may well have changed during that long follow-up period. Third, participants resided in six states (California, Florida, Louisiana, New Jersey, North Carolina, and Pennsylvania) and two metropolitan areas (Atlanta and Detroit). Thus, the cohort may not be truly representative of the entire country. Fourth, the distinction between persons who drank caffeinated coffee and those who drank decaffeinated coffee was subject to misclassification, since these categories were defined on the basis of consumption of either beverage more than half the time. Fifth, there were no data about how coffee was prepared (espresso, boiled, or filtered) and the constituents of coffee may differ according to the method of preparation.
Despite the limitations to observational studies like this one, this is a very large study, and its sheer size strengthens the associations that it demonstrates. If indeed coffee were to cause this reduction in mortality, what could be the potential mechanism? Coffee is a rich source of antioxidants and other bioactive compounds. Some prior studies have shown inverse associations between coffee consumption and serum biomarkers of inflammation, as well as reductions in insulin resistance, diabetes, inflammatory diseases, and stroke. Although other antioxidants have not reduced cardiovascular events in clinical trials, perhaps the particular constituents in coffee succeed where others have failed. Or perhaps a combination of antioxidants and anti-inflammatory actions combine to have salubrious effects.
Importantly, this study does not tell us about other potentially deleterious effects of coffee, such as effects on blood pressure, lipids, or arrhythmias. These should all be taken into account before advocating our patients increase coffee consumption. Although this study does not prove cause and effect of coffee reducing mortality, I feel comfortable continuing my morning coffee ritual.