Approximately 50 million people in the United States have hypertension, and the prevalence is increasing, according to background information in the article. Hypertension is a major risk factor for coronary heart disease, stroke, and congestive heart failure. Therefore, even small reductions in the prevalence of hypertension could have a potentially large public health and financial impact. Several previous studies have indicated a possible association between caffeine intake and the risk of hypertension. Short-term studies have demonstrated that caffeine intake acutely increases blood pressure, but over time, weakening of this effect does occur. A long-term effect of caffeine intake on the risk of developing hypertension would be of substantial public health importance given the widespread consumption of beverages containing caffeine, but currently, studies of this association are scarce.
Wolfgang C. Winkelmayer, M.D., Sc.D., of Brigham and Women's Hospital and the Harvard School of Public Health, Boston, and colleagues conducted a study to determine whether caffeine intake or consumption of certain caffeine-containing beverages is associated with an increased risk of incident hypertension in women. The researchers analyzed data from the Nurses' Health Studies (NHSs) I and II of 155,594 U.S. women free from physician-diagnosed hypertension, who were followed-up over 12 years (1990-1991 to 2002-2003). Caffeine intake and possible confounders were ascertained from regularly administered questionnaires.
Over the 12 years, 19,541 incident cases of physician-diagnosed hypertension were reported in NHS I and 13,536 in NHS II. In both cohorts, no linear association between caffeine consumption and risk of incident hypertens ion was observed after multivariate adjustment. When studying individual classes of caffeinated beverages, habitual coffee consumption was not associated with increased risk of hypertension. By contrast, consumption of cola beverages was associated with an increased risk of hypertension, independent of whether it was sugared or diet cola.
"In this study with more than 1.4 million person-years of follow-up [the number of women in the study times the number of years of follow-up per woman], the relevant exposures and outcomes have been found valid and accurate, and coffee intake was updated to reflect changes in individual behavior. We found strong evidence to refute speculation that coffee consumption is associated with an increased risk of hypertension in women," the authors write.
Concerning the link found between colas and hypertension, the researchers write: "? we speculate that it is not caffeine but perhaps some other compound contained in soda-type soft drinks that may be responsible for the increased risk in hypertension. If these associations are causal, they may have considerable impact on public health."