April 13, 2011 — Habitual drinking of 3 cups/day or more of coffee is not associated with an increased risk for hypertension compared with less than 1 cup/day, but this risk was slightly elevated with light to moderate consumption of 1 to 3 cups/day, according to the results of a systematic review and meta-analysis of prospective observational studies reported online March 30 in the American Journal of Clinical Nutrition.
"In 2 meta-analyses of randomized controlled trials, increased coffee intake was associated with slightly higher blood pressure," write Zhenzhen Zhang, from the Department of Epidemiology, Michigan State University, East Lansing, and colleagues. "However, these trials were short in duration (<85 d). We conducted a systematic review and meta-analyses of long-term prospective studies that examined the association of habitual coffee consumption with risk of hypertension."
Using a standardized protocol, the investigators searched electronic databases through August 2009, including MEDLINE, EMBASE, Agricola, and the Cochrane Library. Inclusion criteria were prospective cohort trials studying the association of coffee drinking with incident hypertension or blood pressure. Six prospective cohort studies met selection criteria. These studies enrolled a total of 172,567 participants, of whom 37,135 had incident hypertension during follow-up, with mean duration ranging from 6.4 to 33.0 years.
With use of the lowest consumption category as a reference (< 1 cup [approximately 237 mL)/day]), pooled relative risks (RRs) for hypertension were 1.09 for the next higher category (1 - 3 cups/day; 95% confidence interval [CI], 1.01 - 1.18); 1.07 for the second-highest category (3 - 5 cups/day; 95% CI, 0.96 - 1.20); and 1.08 for the highest category (> 5 cups/day; 95% CI, 0.96 - 1.21).
There was an inverse "J-shaped" curve of hypertension risk vs coffee intake, based on dose-response meta-analysis (P for quadratic term < .001). Hypertension risk increased up to 3 cups/day (RR for comparison of 3 vs 0 cups/day, 1.07; 95% CI, 0.97 - 1.20) and then decreased with higher intakes (RR for comparison of 6 vs 0 cups/day, 0.99; 95% CI, 0.89 - 1.10).
"The results suggest that habitual coffee consumption of >3 cups/d was not associated with an increased risk of hypertension compared with <1 cup/d; however, a slightly elevated risk appeared to be associated with light-to-moderate consumption of 1 to 3 cups/d," the study authors write.
Limitations of this study include inability to differentiate the effects of caffeinated and decaffeinated coffee, differences in serving size and strength of brew in the United States vs Europe, observational design of the included studies, and possible residual confounding. In addition, no studies controlled for salt intake, and the studies meeting inclusion criteria were all conducted among white populations, limiting generalizability.
"Future studies using different types of coffee and in nonwhite populations are warranted," the study authors conclude.
The Louisiana State University Health Science Center, School of Public Health; the Pennington Biomedical Research Center; and the Center for Human Nutrition, Johns Hopkins Bloomberg School of Public Health, supported this study.
Am J Clin Nutr. Published online March 30, 2011. Abstract
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