Background Obesity, as reflected by a high body mass index (BMI), is a well-known risk factor for endometrial cancer. Whether more precise measures of body fat, such as body fat percentage and fat mass as assessed by bioelectrical impedance analysis, are more strongly related to risk is unknown and has not been explored in any prospective study. In addition, the independent role of body fat distribution in the development of endometrial cancer remains unclear.
Methods We analysed data from 202,796 women in UK Biobank, aged 40–69 years at study entry. Trained personnel collected data on body size and composition. Cox proportional hazard models, with time in study as the underlying time metric, were used to estimate hazard ratios (HR) and corresponding 95% confidence intervals (CIs) for the association of body size and body composition with risk of endometrial cancer. Analyses were stratified by year of birth and year of recruitment and adjusted for age, socio-economic deprivation score, age at menarche, menopausal status and age at menopause, use of oral contraceptive and hormone replacement therapy, diabetes status, physical activity and smoking status. Models that assessed the association of fat distribution measures and fat-free mass on cancer risk were additionally adjusted for BMI in order to examine their independent effects.
Results During a mean follow up of 5.5 years, 651 incident cases of endometrial cancer were identified, with a mean age of diagnosis of 63.1 years. The HR per standard deviation increase in BMI was 1.64 (1.53–1.75) and was comparable to that of body fat percentage (HR=1.73, 95%CI: 1.56–1.90) and fat mass (HR=1.64, 95%CI:1.53–1.76); however, in terms of model fit assessed by likelihood ratio chi square statistics, BMI appeared to be the most informative measure. All measures of fat distribution (waist and hip circumference, waist to hip ratio, waist to height ratio and trunk fat percentage) also showed strong positive associations with endometrial cancer risk (Ptrend <0.001); however, these associations were substantially attenuated after adjusting for BMI (Ptrend >0.10). Fat-free mass, a marker of muscle and bone mass, was also strongly associated with endometrial cancer risk (HR=1.58, 95%CI:1.47–1.69), and the association persisted after adjusting for BMI (HR=1.15, 95%CI: 1.03–1.29).
Conclusion The results of this study support the continued use of BMI in assessing the risk of endometrial cancer associated with obesity.
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