Body mass index and early-onset colorectal cancer risk: a systematic review and cohort-based meta-analysis.

[BACKGROUND] The incidence of early-onset colorectal cancer (EOCRC; ≤50 years) has been increasing globally. High BMI is a recognized predisposing factor for colorectal cancer, but its contribution to EOCRC is not yet fully understood. We conducted an updated systematic review and meta-analysis of cohort studies to clarify the association between BMI and EOCRC risk. Following PRISMA guidelines, PubMed, EMBASE, Scopus, Science Direct, and Web of Science were searched through August 2025. Eligible studies reported BMI measured prior to diagnosis and EOCRC outcomes. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were estimated using random-effects models. Subgroup analyses by sex, region, and age cut-offs were performed.

[RESULTS] Eleven cohort studies were included. In the primary analysis (EOCRC defined as <50 years), compared with normal weight, overweight/obesity (combined as BMI ≥25 kg/m) was significantly associated with higher EOCRC risk (OR = 1.59, 95%CI: 1.25-1.93). Stratified analyses showed a modest increase with overweight (OR = 1.24, 95%CI: 1.07-1.40) and a stronger association with obesity (OR = 1.81, 95%CI: 1.08-2.55). Sensitivity analyses using ≤55 years as the cutoff confirmed robustness of results (OR = 1.63). Sex-specific analyses indicated greater risk among men (OR = 1.50) than women (OR = 1.16). Regional variations were observed, with the strongest associations in North America and Europe.

[CONCLUSIONS] Our findings indicated that elevated BMI could be associated with increased risk of EOCRC, particularly among obese individuals and men. These findings highlight obesity as a modifiable risk factor and underscore the importance of weight management strategies in younger populations to mitigate the rising global burden of EOCRC.