Abstract
BackgroundWe tested the hypothesis that body mass index (BMI) aged 20 years modifies the association of adult weight gain and breast cancer risk.MethodsWe recruited women (aged 47–73 years) into the PROCAS (Predicting Risk Of Cancer At Screening; Manchester, UK: 2009–2013) Study. In 47,042 women, we determined BMI at baseline and (by recall) at age 20 years, and derived weight changes. We estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for new breast cancer using Cox models and explored relationships between BMI aged 20 years, subsequent weight changes and breast cancer risk.ResultsWith median follow-up of 5.6 years, 1142 breast cancers (post-menopausal at entry: 829) occurred. Among post-menopausal women at entry, BMI aged 20 years was inversely associated [HR per SD: 0.87 (95% CI: 0.79–0.95)], while absolute weight gain was associated with breast cancer [HR per SD:1.23 (95% CI: 1.14–1.32)]. For post-menopausal women who had a recall BMI aged 20 years <23.4 kg/m2 (75th percentile), absolute weight gain was associated with breast cancer [HR per SD: 1.31 (95% CIs: 1.21–1.42)], but there were no associations for women with a recall BMI aged 20 years of >23.4 kg/m2 (Pinteraction values <0.05).ConclusionsAdult weight gain increased post-menopausal breast cancer risk only among women who were <23.4 kg/m2 aged 20 years.
Highlights
We tested the hypothesis that body mass index (BMI) aged 20 years modifies the association of adult weight gain and breast cancer risk
We evaluated the validity of assessing BMI at 20 years of age using recalled weight by comparing mean recall BMI distributions against age- and sex-specific BMI distributions in contemporaneous populations (Supplementary Table S2).[22]
The following were noted with increasing BMI aged 20 years: decreasing median age at study entry, proportion who were menopausal, and current users of hormonal replacement therapy (HRT); any type of oophorectomy (P = 0.002); decreasing height (P < 0.001); higher proportion ever user of statins (P < 0.001); lower use of alcohol (P < 0.001); lower median units of any exercise per week (P < 0.001); lower median age at menarche (P < 0.001) and first pregnancy (P < 0.001); and lower proportion who were parous (P < 0.001)
Summary
We tested the hypothesis that body mass index (BMI) aged 20 years modifies the association of adult weight gain and breast cancer risk. Among postmenopausal women at entry, BMI aged 20 years was inversely associated [HR per SD: 0.87 (95% CI: 0.79–0.95)], while absolute weight gain was associated with breast cancer [HR per SD:1.23 (95% CI: 1.14–1.32)]. CONCLUSIONS: Adult weight gain increased post-menopausal breast cancer risk only among women who were
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