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

Abstract

Background: 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.

Patients and methods: 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 four 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.

Results: 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 [95% CI], 1.00 [0.98-1.01]). For specific cancer type, an inverse association was observed for colorectal (0.96 [0.92-0.99]) and aggressive prostate cancer (0.93 [0.87-0.99]). 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 to non-drinkers, 0.1-0.9, 1-1.9, 2-2.9 and ≥3 cup/day of decaffeinated coffee intake were associated with HRs of 1.30 (95% CI, 1.01-1.68), 1.42 (1.00-2.03), 1.43 (0.91-2.23), and 1.79 (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).

Conclusions: 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.