08 May 2011
Those daily extra cups of joe not linked to hypertension
Java lovers will rejoice in a large study's findings that more cups daily isn't associated with increased risk of hypertension. The study, published in American Journal of Clinical Nutrition on March 30, was a systematic review and meta-analysis that examined six prospective cohort studies.
Two previous meta-analyses of randomized controlled trials found an association with slightly raised risk of hypertension. But these trials all lasted only 85 days or fewer days. In the new study, a total 172,567 participants and 37,135 incident cases of hypertension were followed over the course of six years.
Four of the six studies evaluated reported a nonlinear association between coffee consumption and hypertension, whereas two reported no statistically significant association. The pooled results revealed a relative risk of 1.09 (1.01; 1.18) from drinking 1 to 3 cups daily (a slightly elevated risk), 1.07 (0.96, 1.20) from drinking 3 to 5 cups daily, and 1.09 (0.96, 1.21) from drinking five or more cups daily.
The researchers suggested that the results of the study may be explained by coffee drinkers developing a tolerance to caffeine's acute effect on blood pressure, which is thought to be result of caffeine's binding to receptors that trigger a sympathetic nervous system response.
Additionally, another explanation may be that other ingredients in coffee like magnesium, potassium, or flavonoids could have a counterbalancing effect on blood pressure, which the researchers suggest may explain an inverse "J-shape" relationship between habitual coffee drinking and hypertension risk.
Since the way people metabolize caffeine in the liver can depend on genetics, the authors suggest more research is needed to determine coffee's effects on non-white populations.
Zhang Z, Hu G, Caballero B, Appel L, and Chen L. 2011. Habitual coffee consumption and risk of hypertension: a systematic review and meta-analysis of prospective observational studies1–3. Amer J Clin Nutr. doi: 10.3945/ajcn.110.004044.