Obesity at age 20 and weight gain during adulthood increase risk of total and premature all-cause mortality: Findings from women attending breast screening in Manchester

Background: Obesity in early adulthood is associated with lower breast cancer rates in later life. We examined the association between both obesity in early adulthood and body mass index (BMI) change through adulthood, and all-cause mortality. Methods The Predicting Risk of Cancer At Screening (PROCAS) study recruited 57 902 women aged 46-73y (median age 57.2, IQR 51.8–63.7 years) from the Greater Manchester NHS breast screening programme between 2009 and 2015. It was used to assess associations between BMI at 20y and cohort entry with all-cause mortality ascertained via deaths recorded on the National Breast Screening System to June 2020. Hazard ratios were estimated using proportional hazards (Cox) regression adjusted for factors at entry to the cohort: age, deprivation, bilateral oophorectomy, hormone-replacement therapy, menopausal status, ethnicity, alcohol intake, physical activity, and BMI. Results The prevalence of overweight (25-30kg/m 2 ) and obesity (> 30km/m 2 ) were 10.4% and 2.5% at 20y, increasing to 35.2% and 25.9% at cohort entry. After a mean 8.7y follow-up we observed that overweight and obesity at 20y had a higher mortality rate compared with healthy weight (HRs respectively 1.27, 95%CI = 1.10–1.47; 2.11, 1.67–2.66). Women who were underweight/healthy weight at 20y and gained weight to obesity at entry had a slightly increased mortality rate compared with women who were underweight/healthy weight at both time points (HR 1.16, 95%CI = 1.02–1.32). Women with overweight or obesity at both 20y and entry had a higher mortality rate than women who were underweight/healthy weight at both points (HRs respectively 1.36, 95%CI = 1.06–1.75; 1.90, 95%CI = 1.45–2.48). Conclusions Women who self-reported overweight and obesity at 20y had a shorter life expectancy in this cohort of women attending breast cancer screening. Weight gain from 20y was common in this group. Girls and women should be supported to maintain a healthy weight throughout the lifespan to help increase life expectancy. Trial registration number NCT04359420, retrospectively registered 24/04/2020.