Meta-Analyses of Prospective Studies on Cancer Incidence and Caffeinated or Decaffeinated Coffee
Introduction
Many epidemiological studies have investigated the association between coffee consumption and the risk of various types of cancer. However, some study results have been inconsistent. Therefore, we identified high-quality prospective cohort studies and performed meta-analyses to determine the effects of caffeinated and decaffeinated coffee consumption on the incidence of 10 common types of cancer.
Methods
We utilized electronic databases PubMed, Scopus, and Embase to search peer-reviewed prospective cohort studies published through July 2020. To assess the quality of studies, the Newcastle-Ottawa Scale was used. Summary relative risks (SRRs) and 95% confidence intervals (CIs) were calculated using the random-effects model proposed by DerSimonian and Laird.
Results
A meta-analysis of 63 prospective cohort studies for 10 major cancer types showed that there was a 7% decreased risk in total cancer incidence (SRR, 0.93; 95% CI, 0.89–0.97) with overall coffee consumption (caffeinated and decaffeinated). In those who consumed high amounts of caffeinated coffee, there was a 46% reduction in incidence of hepatocellular cancer (SRR, 0.54; 95% CI, 0.39–0.74), 39% reduction in endometrial cancer (SRR, 0.61; 95% CI, 0.44–0.84), and 17% reduction in skin cancer (SRR, 0.83; 95% CI, 0.74–0.92). Intriguingly, decaffeinated coffee consumption had no significant decrease in cancer incidence except a 27% reduction in endometrial cancer incidence (SRR, 0.73; 95% CI, 0.58–0.93). High consumption of overall coffee (caffeinated and decaffeinated) was associated with a 20% increase in incidence of lung cancer (SRR, 1.20; 95% CI, 1.07–1.34). No significant association was found in pancreatic, prostate, colorectal, ovarian, and bladder cancer incidence in relation to any coffee consumption.
Conclusion
Our comprehensive meta-analyses of prospective cohort studies for 10 major cancer types demonstrate that caffeinated coffee has an inverse relationship with cancer incidence in the liver, endometrium, and skin. The observed positive association between high coffee consumption and increased lung cancer incidence is likely due to residual confounding by tobacco smoking. Taken together, these findings can have a major impact on preventive interventions to reduce cancer incidence and subsequent morbidity. Further investigations are needed to clarify why certain cancer types are prevented by coffee consumption while others are not.