Abstract
Background
Epidemiological
studies on the association between coffee intake and cancer risk have
yielded inconsistent results. To summarize and appraise the quality of
the current evidence, we conducted an umbrella review of existing
findings from meta-analyses of observational studies.
Methods
We
searched PubMed, Embase, Web of Science and the Cochrane database to
obtain systematic reviews and meta-analyses of associations between
coffee intake and cancer incidence. For each association, we estimated
the summary effect size using the fixed- and random-effects model, the
95% confidence interval, and the 95% prediction interval. We also
assessed heterogeneity, evidence of small-study effects, and excess
significance bias.
Results
Twenty-eight
individual meta-analyses including 36 summary associations for 26
cancer sites were retrieved for this umbrella review. A total of 17
meta-analyses were significant at P ≤ 0.05 in the random-effects model. For the highest versus lowest categories, 4 of 26 associations had a more stringent P value (P ≤ 10− 6). Associations for five cancers were significant in dose-response analyses. Most studies (69%) showed low heterogeneity (I2 ≤ 50%).
Three and six associations had evidence of excessive significance bias
and publication bias, respectively. Coffee intake was inversely related
to the risk of liver cancer and endometrial cancer and was characterized
by dose-response relationships. There were no substantial changes when
we restricted analyses to meta-analysis of cohort studies.
Conclusions
There
is highly suggestive evidence for an inverse association between coffee
intake and risk of liver and endometrial cancer. Further research is
needed to provide more robust evidence for cancer at other sites.
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