Alcohol intake in early adulthood and risk of colorectal cancer: three large prospective cohort studies of men and women in the United States.

Heavy alcohol consumption in mid-adulthood is an established risk factor of colorectal cancer (CRC). Alcohol use in early adulthood is common, but its association with subsequent CRC risk remains largely unknown. We prospectively investigated the association of average alcohol intake in early adulthood (age 18-22) with CRC risk later in life among 191,543 participants of the Nurses' Health Study ([NHS], 1988-2014), NHSII (1989-2015) and Health Professionals Follow-Up Study (1988-2014). Cox proportional hazards models were used to estimate hazard ratios (HRs) with 95% confidence intervals (CIs), which were pooled using random effects models. We documented 2,624 CRC cases. High alcohol consumption in early adulthood (≥ 15 g/day) was associated with a higher CRC risk (multivariable HR 1.28, 95% CI 0.99-1.66, P = 0.02; P = 0.44), after adjusting for potential confounding factors in early adulthood. Among never/light smokers in early adulthood, the risk associated with high alcohol consumption in early adulthood was elevated (HR 1.53, 95% CI 1.04-2.24), compared with those who had < 1 g/day of alcohol intake. The suggestive higher CRC risk associated with high alcohol consumption in early adulthood was similar in those who had < 15 g/day (HR 1.35, 95% CI 0.98-1.86) versus ≥ 15 g/day of midlife alcohol intake (HR 1.35, 95% CI 0.89-2.05), compared with nondrinkers in both life stages. The findings from these large prospective cohort studies suggest that higher alcohol intake in early adulthood may be associated with a higher risk of developing CRC later in life.