Context: Caffeine acutely increases blood pressure, but the association between habitual consumption of caffeinated beverages and incident hypertension is uncertain.
Objective: To examine the association between caffeine intake and incident hypertension in women.
Design, setting, and participants: Prospective cohort study conducted in the Nurses' Health Studies (NHSs) I and II of 155,594 US women free from physician-diagnosed hypertension followed up over 12 years (1990-1991 to 2002-2003 questionnaires). Caffeine intake and possible confounders were ascertained from regularly administered questionnaires. We also tested the associations with types of caffeinated beverages.
Main outcome measure: Incident physician-diagnosed hypertension.
Results: During follow-up, 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 hypertension was observed after multivariate adjustment (NHS I, P for trend = .29; NHS II, P for trend = .53). Using categorical analysis, an inverse U-shaped association between caffeine consumption and incident hypertension was found. Compared with participants in the lowest quintile of caffeine consumption, those in the third quintile had a 13% and 12% increased risk of hypertension, respectively (95% confidence interval in NHS I, 8%-18%; in NHS II, 6%-18%). 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 (P for trend <.001).
Conclusion: No linear association between caffeine consumption and incident hypertension was found. Even though habitual coffee consumption was not associated with an increased risk of hypertension, consumption of sugared or diet cola was associated with it. Further research to elucidate the role of cola beverages in hypertension is warranted.