Decaffeinated coffee consumption and risk of total and site-specific cancer

Coffee is generally considered safe regarding cancer risk. However, concerns have emerged over methylene chloride, a chemical used in decaffeination, due to its carcinogenic properties. The potential cancer risk from methylene chloride residue in decaffeinated coffee remains unclear.

This prospective cohort study included 75 988 women (Nurses' Health Study, 1984-2020) and 45 349 men (Health Professionals Follow-up Study, 1986-2020). Decaffeinated coffee consumption was assessed at baseline and every 4 years using a validated food frequency questionnaire. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of total and 14 site-specific cancers associated with decaffeinated coffee consumption, adjusted for regular coffee intake and other potential confounding variables.

During up to 36 years of follow-up, we documented 34 120 incident cancer cases (22 688 in women and 11 432 in men). Overall, decaffeinated coffee intake was not associated with higher total cancer risk [per 1 cup/day higher intake, HR 1.00 (95% CI 0.98-1.01)]. For specific cancer type, an inverse association was observed for colorectal [HR 0.96 (95% CI 0.92-0.99)] and aggressive prostate [HR 0.93 (95% CI 0.87-0.99)] cancer. An observed higher lung cancer risk for decaffeinated coffee attenuated to null when restricted to never smokers. However, we observed elevated bladder cancer risk among male never smokers: compared with nondrinkers, 0.1-0.9, 1-1.9, 2-2.9 and ≥3 cups/day of decaffeinated coffee intake were associated with HRs of 1.30 (95% CI 1.01-1.68), 1.42 (95% CI 1.00-2.03), 1.43 (95% CI 0.91-2.23), and 1.79 (95% CI 0.92-3.50), respectively, with borderline significant linear trends (P_trend = 0.06). This positive association remained robust in various sensitivity analyses and became even stronger with an 8-year lag. No association between decaffeinated coffee and bladder cancer was observed among women (P_{sex-heterogeneity} = 0.03).

Higher decaffeinated coffee intake was not associated with total cancer risk. However, the observed significant higher risk of bladder cancer in men warrants further studies.