Abdominal obesity and colorectal cancer risk: a systematic review and updated meta-analysis

This meta-analysis investigates the association between abdominal obesity, as measured by waist circumference (WC) and waist-to-hip ratio (WHR), and the risk of colorectal cancer (CRC). We systematically searched PubMed, Scopus, and Google Scholar for relevant English-language prospective cohort studies. Nine studies met the inclusion criteria for the primary meta-analysis, comprising 13,193,908 participants with 131,438 incident CRC cases. Pooled relative risks (RRs) and 95% confidence intervals (CIs) were estimated using a random-effects model. Central obesity was associated with a 31% increased risk of CRC (RR = 1.31; 95% CI: 1.25–1.37). The risk was higher in men (RR = 1.41; 95% CI: 1.31–1.52) than in women (RR = 1.26; 95% CI: 1.19–1.34; P for subgroup difference = 0.04). The association was stronger for colon cancer (RR = 1.37; 95% CI: 1.27–1.47) than for rectal cancer (RR = 1.18; 95% CI: 1.11–1.26; P < 0.001). Waist circumference specifically showed a 32% increased risk (RR = 1.32; 95% CI: 1.25–1.41). Studies using measured WC/WHR reported a higher risk (RR = 1.48; 95% CI: 1.36–1.61) than those using self-reported measures (RR = 1.26; 95% CI: 1.20–1.32; P < 0.001). No significant heterogeneity was found by exposure type (WC vs. WHR) or geographic region. Central obesity is a significant and independent risk factor for colorectal cancer, with stronger associations observed for colon cancer than for rectal cancer and higher relative risks in men than in women. Visceral fat appears to play a critical role in colorectal carcinogenesis. Maintaining a healthy waist circumference through regular physical activity and a balanced diet remains a key strategy to reduce CRC risk.