Pre-diagnostic body mass index and weight change in relation to colorectal cancer survival among incident cases from a population-based cohort study

Background Whether excess body weight influences colorectal cancer (CRC) survival is unclear. We studied pre-diagnostic body mass index (BMI) and weight change in relation to CRC-specific mortality among incident CRC cases within a large, Norwegian cohort. Methods Participants’ weight was measured at health examinations up to three times between 1974 and 1988. CRC cases were identified through linkage with the Norwegian Cancer Registry. In total, 1336 men and 1180 women with a weight measurement >3 years prior to diagnosis were included in analyses. Hazard ratios (HRs) and confidence intervals (CIs) were estimated with Cox regression. Results During a mean follow-up of 5.8 years, 507 men and 432 women died from CRC. Obesity (BMI ≥30 kg/m 2 ) was associated with higher CRC-specific mortality than normal weight (BMI 18.5–25 kg/m 2 ) in men with proximal colon cancer, HR = 1.85 (95 % CI 1.08–3.16) and in women with rectal cancer, HR = 1.93 (95 % CI 1.13–3.30). Weight gain was associated with higher CRC-specific mortality in women with CRC, colon cancer, and distal colon cancer, HRs per 5 kg weight gain were 1.18 (95 % CI 1.01–1.37), 1.22 (95 % CI 1.02–1.45), and 1.40 (95 % CI 1.01–1.95), respectively. Weight gain was not significantly associated with survival in men. Conclusions Maintaining a healthy weight may benefit CRC survival, at least in women.