Coffee, tea, caffeine, and risk of hypertension: The Singapore Chinese Health Study

Purpose The relationship between coffee and tea, and risk of hypertension remains controversial in Western populations. We investigated these associations in an Asian population. Methods The Singapore Chinese Health Study is a population-based prospective cohort that recruited 63,257 Chinese aged 45-74 years and residing in Singapore from 1993 to 1998. Information on consumption of coffee, tea, and other lifestyle factors was collected at baseline, and self-reported physician-diagnosed hypertension was assessed during two follow-up interviews (1999-2004, 2006-2010). Results We identified 13,658 cases of incident hypertension after average 9.5 years. Compared to those who drank one cup of coffee/day, the hazard ratios (HR) and 95% confidence intervals (CI) were 0.87 (0.83-0.91) for < weekly drinkers and 0.93 (0.86-1.00) for >= 3 cups/day drinkers. Compared to < weekly drinkers, daily drinkers of black or green tea had slight increase in risk, but these risk estimates were attenuated and became non-significant after adjustment for caffeine. After adjusting for coffee, there was a stepwise dose-response relationship between caffeine intake and hypertension risk; compared to the lowest intake (< 50 mg/day), those in the highest intake (>= 300 mg/day) had a 16% increase in risk; HR 1.16, 95% CI 1.04-1.31 (p trend = 0.02). Conclusions Drinking coffee < 1 cup/week or >= 3 cups/day had lower risk than drinking one cup/day. Caffeine may account for increased risk in daily tea drinkers and in those who drank one cup of coffee/day. The inverse U-shaped association with coffee suggests that at higher doses, other ingredients in coffee may offset the effect of caffeine and confer benefit on blood pressure.