P70 Body size and composition, physical activity and sedentary time in relation to endogenous hormones in pre- and post-menopausal women: findings from the UK Biobank

Abstract

Background Anthropometric and lifestyle factors may influence cancer risks through hormonal changes but the evidence to date is not conclusive. We therefore investigated associations of body size and composition, physical activity and sedentary time with serum hormone concentrations in pre- and post-menopausal women. Methods Design: Cross-sectional. Setting: UK Biobank, a large prospective cohort study involving about 500,000 adults aged between 40–69 years when recruited in 22 assessment centres between 2006 and 2010. Participants: 20,758 pre-menopausal and 71,101 post-menopausal women, of whom 4,803 (23%) and 15,469 (22%) respectively had accelerometer data. Exposures: body mass index (BMI), height, waist to height ratio, waist to hip ratio, body fat mass, trunk fat mass, self-reported and accelerometer-measured physical activity and self-reported sedentary time. Outcomes: serum concentrations of total and calculated free oestradiol, total and calculated free testosterone, sex hormone binding globulin (SHBG) and insulin-like growth factor-1 (IGF-1). Statistical analysis: Multivariable linear regression analysis. Results The exposure-outcome associations are reported only if there was at least a 5% difference in hormone concentrations between the highest and lowest exposure groups. In pre-menopausal women, higher BMI was associated with a lower concentration of total oestradiol (15% difference in the highest vs. lowest BMI group, i.e., 35+ kg/m2 vs Self-reported physical activity was associated with somewhat lower concentrations of total and calculated free testosterone (pre-menopausal 10% (free testosterone), post-menopausal 5% and 11% respectively in the most vs. least active quartile) and a higher concentration of SHBG (premenopausal 11%, postmenopausal 10%), and the opposite was true for self-reported sedentary time. The associations were slightly stronger with accelerometer-measured physical activity, but were attenuated after adjustment for BMI. Ptrend for all reported associations was Conclusion This study confirms strong associations between adult anthropometric factors and hormone and SHBG concentrations in both pre- and post-menopausal women; this may partly explain the effects of these factors on cancer risks. The associations with physical activity and sedentary time were at most modest.