Parity, age at first birth, breastfeeding, and risk of major osteoporotic fractures in middle-aged women. The HUNT study

This population-based cohort study investigated the associations of parity, age at first birth, and breastfeeding duration with risk of major osteoporotic fractures in Norwegian women. Higher parity, higher age at first birth, and longer breastfeeding duration were associated with modestly reduced fracture risk. PURPOSE: Reproductive factors may influence long-term bone health, yet studies on their associations with fracture risk have yielded inconsistent results. This study examined associations between parity, age at first birth, and lifetime breastfeeding duration with risk of major osteoporotic fractures in Norwegian women. METHODS: We included 41,274 women aged ≥ 45 years in the Trøndelag Health Study (HUNT) linked with the Medical Birth Registry of Norway and hospital-based fracture records. We used Cox proportional hazards regression to estimate hazard ratios (HRs) with 95% confidence intervals (CIs) for first major osteoporotic fracture (MOF) in hip, spine, proximal humerus, or distal forearm. RESULTS: A total of 7520 MOF occurred during 501,204 person-years (median follow-up time: 12.3 years). Compared to women with two births, those with four births had lower fracture risk (HR: 0.92, 95% CI: 0.86-0.98). Each additional birth was associated with reduced fracture risk (HR: 0.98, 95% CI: 0.96-0.99). Women with first birth at age ≥ 30 showed HR of 0.92 (95% CI: 0.85-1.00) compared to those with first birth at ages 20-24. Women with the longest breastfeeding duration (≥ 21 months) had lower fracture risk (HR: 0.89, 95% CI: 0.76-1.02) compared to those who never breastfed. CONCLUSION: Higher parity, later age at first birth, and longer breastfeeding duration were each associated with modest reductions in fracture risk after adjusting for potential confounding factors. These findings suggest that reproductive history may have long-lasting effects on women's skeletal health and could be considered in fracture risk assessment.