Obesity carries greater risk of colorectal cancer in post- vs premenopausal women

Obesity contributes to a significant increase in the risk of colorectal cancer (CRC) in postmenopausal than in premenopausal women, a study has found.

The study looked at 1,418,180 premenopausal (mean age, 43.7 years) and 4,854,187 postmenopausal women (mean age, 59.9 years) from the Korean National Health Insurance System Cohort. The mean body mass index (BMI) was 23.1 kg/m² in the premenopausal group and 24.1 kg/m² in the postmenopausal group, while the mean waist circumference (WC) was 75 cm and 79.6 cm, respectively.

Over a mean follow-up of 7.2 years, 7,094 premenopausal women and 57,449 postmenopausal women developed CRC. There were cases of incident colon cancer in 6,250 and 49,365 women and incident rectal cancer in 1,418 and 15,055 women, respectively.

In Cox proportional hazards models, compared with a healthy waist size (65–75 cm), increasing WCs conferred a greater risk of CRC on the premenopausal group (<65 cm: hazard ratio [HR], 1.01; 75–85 cm: HR, 1.02; 85–95 cm: HR, 1.09; >95 cm: HR, 1.31) and the postmenopausal group alike (<65 cm: HR, 1.01; 75–85 cm: HR, 1.09; 85–95 cm: HR, 1.19; >95 cm: HR, 1.30).

Relative to a healthy BMI (18.5–22.9 kg/m²), increasing BMIs also posed a greater risk of CRC but only in the postmenopausal group (<18.5 kg/m²: HR, 0.99; 23–25 kg/m²: HR, 1.05; 25–30 kg/m²: HR, 1.11; >30 kg/m²: HR, 1.20). This association was weaker in the premenopausal group (<18.5 kg/m²: HR, 0.99; 23–25 kg/m²: HR, 0.99; 25–30 kg/m²: HR, 0.98; >30 kg/m²: HR, 1.06).

Additional investigation into the precise mechanism of the association between obesity and the incidence of CRC is warranted.