Central obesity measures, including waist circumference and waist-to-hip ratio, showed higher colorectal cancer risks (population attributable fractions = 17.3% and 17.6%) compared with body mass index (9.9%), according to a recent study.

Researchers examined whether colorectal cancer (CRC) cases attributed to obesity, as measured by body mass index (BMI), were underestimated compared with central obesity metrics, including waist circumference (WC) and waist-to-hip ratio (WHR). The analysis utilized data from 458,543 patients aged 40 to 69 years from the UK Biobank cohort, collected between 2006 and 2010, with follow-up extending over a median of 11.8 years.

Published in JAMA Network Open, the study calculated hazard ratios (HR) and population attributable fractions (PAF) for CRC incidence associated with BMI, WC, and WHR. Anthropometric data were collected during baseline assessments using standardized methods, and cancer diagnoses were identified through national registries. To address potential reverse causation caused by prediagnostic weight loss, the researchers performed sensitivity analyses excluding up to the first 7 years of follow-up.

Key findings demonstrated that HRs for CRC were stronger for central obesity metrics compared with for BMI, noted lead study author Fatemeh Safizadeh, of the Division of Clinical Epidemiology and Aging Research at the German Cancer Research Center and Medical Faculty Heidelberg at Heidelberg University in Germany, and  colleagues. The HRs for the highest vs lowest quartiles were 1.23 (95% confidence interval [CI] = 1.14–1.33) for BMI, 1.37 (95% CI = 1.27–1.49) for WC, and 1.40 (95% CI = 1.29–1.51) for WHR. Excluding the initial 7 years of follow-up, the HR for BMI increased to 1.37 (95% CI = 1.22–1.53), aligning more closely with central obesity measures. These adjustments accounted for potential biases linked to cancer-related cachexia.

The PAFs for CRC also varied by obesity metric. For the full follow-up period, PAFs were 9.9% (95% CI = 5.5–14.4%) for BMI, 17.3% (95% CI = 12.3–22.1%) for WC, and 17.6% (95% CI = 12.9–22.2%) for WHR. After excluding the first 7 years, PAFs increased to 15.7% (95% CI = 8.9–22.4%) for BMI, 16.9% (95% CI = 9.8–23.8%) for WC, and 18.0% (95% CI = 11.5–24.6%) for WHR.

The researchers concluded that central obesity measures more comprehensively reflect CRC risk attributable to excess weight. These findings highlighted the importance of incorporating WC and WHR into clinical and public health approaches to CRC prevention, as reliance on BMI alone may underestimate the obesity-related burden of CRC.

Full disclosures can be found in the published study.