Coffee is more beneficial than harmful to health, except during pregnancy
Coffee drinking appears to be generally safe within usual levels of intake and is more likely to benefit health than harm, except during pregnancy and in women at increased risk of fracture, according to the results of an umbrella review of meta-analysis of multiple health outcomes.
“Beneficial associations between coffee consumption and liver outcomes (fibrosis, cirrhosis, chronic liver disease and liver cancer) have relatively large and consistent effect sizes compared with other outcomes,” researchers said. “Consumption is also beneficially associated with a range of other health outcomes and importantly does not seem to have definitive harmful associations with any outcomes outside of pregnancy.”
After accessing PubMed, Embase, CINAHL, Cochrane Database of Systematic Reviews and screening of references, the umbrella review identified a total of 201 meta-analyses of observational research with 67 unique health outcomes and 17 meta-analyses of interventional research with nine unique outcomes.
Across various exposures (high vs low, any vs none and one extra cup a day), coffee intakes were more often associated with benefit than harm for a range of health outcomes. Evidence of a nonlinear association between consumption and some outcomes existed. [BMJ 2017;359:j5024]
Summary estimates showed that drinking three to four cups a day vs none had the largest relative risk reduction for outcomes including all-cause mortality (relative risk [RR], 0.83; 95 percent CI, 0.83–0.88), cardiovascular mortality (RR, 0.81; 0.72–0.90) and cardiovascular disease (RR, 0.85; 0.80–0.90). In addition, there was an 18-percent lower risk of incident cancer (RR, 0.82; 0.74–0.89) associated with high vs low consumption. Coffee drinking also correlated with a reduced risk of several specific cancers and neurological, metabolic, and liver conditions.
Adequate adjustment for smoking largely reversed harmful associations, except in pregnancy, where high vs low/no consumption correlated with low birth weight (odds ratio [OR], 1.31; 1.03–1.67), preterm birth in the first (OR, 1.22; 1.00–1.49) and second (OR, 1.12; 1.02–1.22) trimester, and pregnancy loss (OR, 1.46–1.99). An association also existed between coffee intake and fracture risk in women but not in men.
“Overall, there is no consistent evidence of harmful associations between coffee consumption and health outcomes, except for those related to pregnancy and for risk of fracture in women,” researchers said. “After adjustment for smoking, consumption in pregnancy seems to be associated with harmful outcomes related to low birth weight, preterm birth and pregnancy loss. [PLoS One 2015;10:e0132334; Am J Clin Nutr 2010;92:1120-1132; Int J Gynaecol Obstet 2015;130:116-122]
Containing a complex mixture of bioactive compounds, coffee has been shown to contribute a sizable proportion of daily intake of dietary antioxidant, which is greater than tea, fruit and vegetables. Its most abundant antioxidant, chlorogenic acid, gets degraded by roasting, but alternative antioxidant organic compounds are formed. [J Nutr 2004;134:562-567; J Agric Food Chem 2015;63:1996-2005]
“Caffeine also has significant antioxidant effects. The diterpenes, cafestol and kahweol, induce enzymes involved in carcinogen detoxification and stimulation of intracellular antioxidant defence, contributing towards an anticarcinogenic effect,” researchers said. [Food Chem Toxicol 2002;40:1155-1163]
“These antioxidant and anti-inflammatory effects are also likely to be responsible for the mechanism behind the beneficial associations between coffee consumption and liver fibrosis, cirrhosis, and liver cancer that our umbrella review found had the greatest magnitude of effect compared with other outcomes,” they added. [Nutrients 2017;9:85]