LAUSR

Purpose This study aimed to investigate the association between long-term excess body fat and breast cancer risk by studying adult weight gain together with the subsequent weight fluctuations. Methods Weight gain measure in three different time periods in adulthood of 1500 participants was collected in a case–control study of Western China. Logistic regression models were used to estimate odds ratios and 95% CIs. Results The increased risk of postmenopausal BC was associated with adult weight gain at 5 years and at 10 years before enrollment (OR 1.24, 95% CI 1.03–1.49 per 5 kg increase; OR 1.40, 95% CI 1.14–1.70 per 5 kg increase) but was not associated with adult weight gain at enrollment (OR 0.97, 95% CI 0.81–1.16 per 5 kg increase). Only a positive association was observed in premenopausal women who had gained > 5.0 kg at 10 years before enrollment (OR 1.61, 95% CI 1.10–2.35). Women who had gained > 5.0 kg at 10 years before enrollment and continued to gain during the subsequent 5 years had the highest postmenopausal BC risk (OR 3.34, 95% CI 1.58–7.08). Conclusion Adult weight gain at 5 years and 10 years before enrollment are more closely associated with postmenopausal BC risk than adult weight gain at enrollment in Western China. Controlling body weight as early as possible throughout adulthood to keep weight gain not more than 5.0 kg is particularly necessary for Chinese women.