Colorectal cancer (CRC) is the fourth most common cancer in the UK according to Cancer Research UK, representing up to 12% of total cancer cases from 2017 to 2019.
Overweight and obesity are known risk factors, but sex differences in risk have been observed, with overweight/obesity a stronger risk factor in men. Overweight/obesity is typically measured using body mass index (BMI), but this measurement has limitations as it does not consider fat distribution. As a result, it is unclear how central obesity contributes to CRC risk, or whether it even drives the risk of overweight/obesity in CRC.
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Central obesity can be measured with waist-to-hip ratio (WHR) and waist circumference (WC). Few studies are focusing on the associations that BMI, WHR and WC have with CRC, and they have been limited by low sample sizes and a lack of sex-specificity in results. In research published in November 2024 in Nature, Safizadeh and colleagues assessed the associations that BMI, WHR and WC have with CRC risk in a large dataset, including sex specification. The study found that WHR was strongly associated with CRC risk in both men and women, while BMI had weak associations with CRC risk.
For women, BMI had no significant associations with increased risk of CRC
To observe the effects of BMI, WHR and WC on CRC risk, the study utilised data from the UK Biobank, a large prospective population-based cohort study that recruited more than 500,000 participants ages between 40 and 69 years from 2006 to 2010. This data was then linked to national cancer registries and hospital data to identify CRC cases up to 2021 for England and Scotland, and up to 2016 for Wales.
BMI was categorised according to the World Health Organization (WHO) classification, with 25 to 29kg/m² categorised as overweight and ≥30kg/m² categorized as obese. WHR and WC were classified using sex-specific categories, for example high WHR being 0.95 to 0.99 and very high WHR being ≥1.00 in men, and high WHR being 0.80 to 0.84 and very high WHR being ≥0.85 in women.
Of the 460,784 participants included in the analysis, 5,977 participants developed CRC. Each standard deviation increase in BMI was associated with a hazard ratio (HR) of 1.10, which decreased to an HR of 1.04 after adjusting for the effects of WHR. For WHR, each standard deviation increase was associated with an HR of 1.18, which decreased to 1.15 after adjusting for BMI. For women in particular, BMI had no significant associations with increased risk of CRC before and after adjustment, but WHR did have a significant association with increased risk of CRC with an HR of 1.09 after adjustment.
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By GlobalData140,000 annual CRC cases are predicted in the UK by 2031
The study by Safizadeh and colleagues shows that WHR is a strong predictor of CRC risk and that the use of WHR could better identify women who are at risk of CRC. This may indicate that WHR is a more important risk factor for CRC than BMI, which emphasises the importance of using multiple measures of obesity in clinical practice. However, it is important to consider that this study only used one-time measurements, which does not consider WHR/WC/BMI changes during follow-up.
GlobalData epidemiologists forecast that in the UK, the five-year diagnosed prevalent cases of CRC in men and women ages 18 years and older will increase from 120,000 cases in 2024 to 140,000 cases in 2031.
