Adulthood Weight Change and Risk of Colorectal Cancer in the Nurses' Health Study and Health Professionals Follow-up Study.

We investigated the association between adulthood weight change and colorectal cancer risk in a prospective study with 24 to 34 years of follow-up among 90,988 women and 46,679 men. The primary exposures included weight change from early adulthood (age = 18 years for women, 21 years for men) to baseline enrollment (median age = 43 years for women, 52 years for men), and from baseline to present. In the secondary analyses, we also assessed 4-year weight change during follow-up, and during premenopausal (from age 18 years to menopause) and postmenopausal (from menopause to present) periods in women. Compared to men maintaining their weight from age 21 to baseline, those who gained 20 kg or more were at a higher risk of colorectal cancer (relative risk [RR], 1.64; 95% confidence interval [CI], 1.15-2.35, Ptrend < 0.001), whereas those who lost 8 kg or more had a lower risk (RR, 0.61; 95% CI, 0.30-1.22, Ptrend = 0.003). Similar but weaker associations were found in women and the corresponding RRs were 1.38 (95% CI, 1.13-1.69, Ptrend < 0.001) and 0.80 (95% CI, 0.58-1.09, Ptrend = 0.21). Weight change from baseline to present was not associated with colorectal cancer risk. Four-year weight change during follow-up was positively associated with colorectal cancer risk in men (Ptrend = 0.03) but not in women (Ptrend = 0.42). In addition, in women, weight change before, but not after, menopause was associated with colorectal cancer risk. Our findings provide further scientific rationale for recommendations to maintain a healthy body weight during adulthood. A potential differential association according to sex and timing of weight change warrants further investigation.