Weight change in adulthood and risk of postmenopausal breast cancer: the HUNT study of Norway

BACKGROUND: Adult weight gain is associated with increased risk of postmenopausal breast cancer. Most previous studies are limited by using recalled or self-reported data, and it is not known if age-specific weight changes are important for breast cancer risk. METHODS: In a Norwegian cohort of 28 153 women (and 900 incident breast cancers) with longitudinal anthropometric measurements over up to 30 years, we studied both overall and age-related weight changes in adulthood and risk of postmenopausal breast cancer. RESULTS: Overall, weight gain in adulthood was associated with increased breast cancer risk (hazard ratio (HR) per kg per year 1.31, 95% confidence interval (CI) 1.11–1.54). Weight gain before (HR per kg per year 1.38, 95% CI 1.09–1.75) or around menopause (1.69, 95% CI 1.32–2.16) was associated with increased risk, but there was no clear risk increase associated with later weight gain (HR per kg per year 0.92, 95% CI 0.73–1.18). CONCLUSION: Weight gain in adulthood was associated with increased risk of breast cancer. Our results suggest that weight gain before and around menopausal age may be particularly important for breast cancer risk among postmenopausal women.