title: Parity, lactation, bone strength, and 16-year fracture risk in adult women: findings from the Study of Women's Health Across the Nation (SWAN).
abstract: Our objective was to examine the associations of lifetime parity and accumulated length of lactation with bone strength in women prior to the menopause transition and fracture risk during and after the transition. Participants were 2239 pre- or early peri-menopausal women from the Study of Women's Health Across the Nation (SWAN), ages 42-53 years at baseline, who had no childbirths after age 42. Bone mineral density (BMD) was measured in the femoral neck and the lumbar spine at the baseline SWAN visit using dual-energy x-ray absorptiometry, and the composite indices of femoral neck strength relative to load (in three failure modes: compression, bending, and impact) were calculated from femoral neck BMD, femoral neck size, and body size. Data on fractures after age 42 were collected for a median follow-up of 15.7 years (interquartile range, 11.4-18.5 years). In multiple linear regressions adjusted for covariates, lifetime parity was associated positively with femoral neck strength relative to load (0.024 standard deviation (SD) increment in impact strength index per childbirth, p=0.049), but accumulated length of lactation was associated negatively with lumbar spine BMD (0.018 SD decrement per every additional 6 months of lactation, p=0.040). In Cox proportional hazards regressions adjusted for covariates, neither parity nor lactation was associated with fracture hazard after age 42. In conclusion, parity and lactation have little impact on peak bone strength prior to menopause, and do not affect fracture risk after age 42 over 16-year follow-up.
authors.affiliation: Department of Medicine/Division of General Internal Medicine, Kameda Medical Center, 929 Higashi-cho, Kamogawa, Chiba 296-8602, Japan. Electronic address: takahiromori@outlook.com.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Mori
authors.affiliation: Department of Geriatric Medicine, Graduate School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Ishii
authors.affiliation: Department of Medicine/Division of Geriatrics, David Geffen School of Medicine at UCLA, 10945 Le Conte Ave, Ste. 2339, Los Angeles CA 90095, USA.
authors.forename: Gail A
authors.initials: GA
authors.lastname: Greendale
authors.affiliation: Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, 130 DeSoto Street, A510 Crabtree Hall, Pittsburgh, PA 15260, USA.
authors.forename: Jane A
authors.initials: JA
authors.lastname: Cauley
authors.affiliation: Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, 130 DeSoto Street, A510 Crabtree Hall, Pittsburgh, PA 15260, USA.
authors.forename: Kristine
authors.initials: K
authors.lastname: Ruppert
authors.affiliation: Department of Medicine/Division of General Internal Medicine and Health Services Research, David Geffen School of Medicine at UCLA, 911 Broxton Ave, 1st floor, Los Angeles, CA 90024, USA.
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Crandall
authors.affiliation: Department of Medicine/Division of Geriatrics, David Geffen School of Medicine at UCLA, 10945 Le Conte Ave, Ste. 2339, Los Angeles CA 90095, USA.
authors.forename: Arun S
authors.initials: AS
authors.lastname: Karlamangla
mesh_terms: D000328:Adult; D001842:Bone and Bones / Q000502:physiology*; D005260:Female; D050723:Fractures, Bone / Q000453:epidemiology*; D006801:Humans; D008875:Middle Aged; D010298:Parity; D011446:Prospective Studies; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D016387:Women's Health
keywords: Bone mineral density; Bone strength; Composite strength indices; Fracture; Lactation; Parity