BOSTON, MA — People with a moderately increased intake of coffee—caffeinated, decaffeinated, or overall—have a significantly lower mortality risk than coffee nondrinkers, according to a pooled analysis of three large well-known cohort studies.
The inverse association between coffee intake and mortality applied not only to all-cause mortality, but mortality from cardiovascular or neurologic causes specifically. Notably in the analysis, the association was more pronounced among people who had never smoked.
Based on about 200,000 participants and 20 to 30 years of follow-up, "we were able to provide solid evidence for the association between coffee drinking and the risk of mortality, and the large sample size allowed us to conduct analysis among never-smokers to strip out the confounding factor of smoking," Dr Ming Ding (Harvard School of Public Health, Boston, MA) told heartwire from Medscape in an email.
That said, observed Ding, who is lead author on the study's November 16, 2015 publication in Circulation, the evidence is from an observational analysis and so any coffee-mortality relationships are only hypothesis-generating until they are confirmed in more definitive studies.
In all, 31,956 deaths were recorded during 4,690,072 person-years of follow-up in a pooled cohort consisting of 74,890 women in the Nurses' Health Study (NHS), 93,054 women in the Nurses' Health Study II, and 40,557 men in the Health Professionals Follow-Up Study.
In an initial analysis adjusted for age, drinkers of coffee at the highest levels, for all coffee and for caffeinated coffee only, had a higher all-cause mortality across the three cohorts, according to the researchers. But further adjustment for smoking significantly altered that relationship.
Relative to no consumption of coffee, the pooled hazard ratio (HR) for mortality was:
That worked out to a 0.98 (95% CI 0.97–0.99) risk per one-cup increase (P<0 .001="" and="" both="" caffeinated="" coffee="" decaffeinated="" for="" group="" linear="" p="" reported.="" results="" separately="" similar="" the="" trend="" were="">
Smoking A Strong Confounder
Investigators repeated the multivariate analysis among never-smokers. "Overall, the association of total coffee, caffeinated coffee, and decaffeinated coffee consumption with risk of all-cause mortality changed from a nonlinear association in the overall population to a linear inverse association when restricted to never-smokers," according to Ding et al.
Also strictly among never-smokers, coffee consumption was inversely associated with the risk of mortality due to each of cardiovascular disease, neurological disease, and suicide. For cardiovascular disease, the mortality HR was:
In the current analysis for the cohorts overall, the coffee-intake and mortality relationship was nonlinear, in that mortality declined up to moderate coffee consumption but attenuated such that there wasn't a correlation between the highest levels of consumption and mortality, the group writes.
"And given that this association became linear and inverse after restricting the analysis to never-smokers, it is likely that the nonlinear association observed in the total population was due to the residual confounding by smoking."
Ding said he was not surprised that the associations between caffeinated and decaffeinated coffee consumption were similar for total and cause-specific mortality, in that "other components rather than caffeine might be responsible for coffee's effect on mortality."
For example, he noted, chlorogenic acid and lignans in coffee have antioxidant effects, and they reduce insulin resistance and systemic inflammation in animal models. "Those nutrients therefore might be responsible for the inverse association between coffee and mortality that we saw," Ding proposed.
The study was funded by the National Institutes of Health. The authors had no relevant financial relationships.0>