The underestimated impact of excess body weight on colorectal cancer risk: Evidence from the UK Biobank cohort

Background The association between excess weight and colorectal cancer (CRC) risk may have been underestimated due to potential weight loss during pre-clinical sojourn time of CRC. We aimed to investigate this association and the corresponding population attributable fraction (PAF), accounting for prediagnostic weight loss. Methods Data from the UK Biobank prospective cohort were used. Multivariable adjusted hazard ratios (HR) and their 95% confidence intervals (CI) for various periods of follow-up and the corresponding PAF of excess weight were calculated. Results During a median of 10.0 years of follow-up, of 453,049 participants, 4794 developed CRC. The excess weight–CRC association became substantially stronger with including increasing lengths of follow-up in the analyses and further excluding the initial years of follow-up. HRs (95% CIs) for overweight and obesity were 1.06 (0.97–1.16) and 1.14 (1.03–1.26) after 7 years of follow-up, 1.13 (1.05–1.21) and 1.23 (1.14–1.33) when including complete follow-up length, and 1.26 (1.12–1.43) and 1.42 (1.24–1.63) when excluding the initial 7 years of follow-up. The corresponding PAFs of excess weight were estimated as 6.8%, 11.3%, and 19.0%, respectively. Conclusions Comprehensive consideration of the potential effect of prediagnostic weight loss discloses a much stronger impact of excess body weight on CRC risk than previously assumed.