Reproductive factors and their associations with osteoporosis and osteoarthritis in women

Women are at higher risk of both osteoporosis and osteoarthritis (OA) compared with age-matched males. Sex hormones and reproductive factors may partly explain these differences. This study therefore aimed to investigate reproductive factors including parity, menstrual regularity, use of oral contraceptives (OC) and hormone replacement therapy (HRT) and their associations with bone mass, cartilage and radiographic OA in populationbased samples of both young and older women. Young women aged 26 to 36 years were selected from the Childhood Determinants of Adult Health (CDAH) study, a 20-year follow-up of children who participated in 1985 Australian Schools Health and Fitness Survey (ASHFS). Older women aged 50 to 80 years were selected from the Tasmanian Older Adult Cohort (TASOAC) study, an ongoing prospective study in southern Tasmania. Parity, menstrual regularity and use of OC and HRT were assessed by self-administered questionnaire. Bone mass was measured by quantitative ultrasound (QUS) for young women and bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA) for older women. Knee cartilage volume and cartilage defects were measured by magnetic resonance imaging (MRI) for both young and older women and radiographic OA was assessed by X-ray only for older women. Key findings were: ‚Äö Young women: o Current use of OC was associated with higher bone mass. o Irregular menstrual cycles were associated with higher bone mass and the association was partially mediated by markers of androgen status especially free testosterone. o Parity was positively associated with cartilage defects primarily at the patella site. Women with three or more children had the highest prevalence of cartilage defects. ‚Äö In older women: o Ever use and duration of OC use were associated with higher BMD in the spine and total body measured at age 50-80 years. o OC use for five to ten years was associated with a reduction of vertebral fracture. o Parity was associated with lower cartilage volume primarily in the tibial compartment and the associations were dose-dependent. o Parity was associated with higher cartilage defects only in the patella compartment. o There were no associations between parity and osteophytes or joint space narrowing (JSN). o Use of OC and HRT was not associated with knee cartilage volume, cartilage defects or radiographic OA including JSN and osteophytes. In conclusion, these cross-sectional analyses of population-based samples of both young and older women showed use of OC was associated with higher bone mass suggesting a protective effect of OC use on bone health. In young women, menstrual irregularity was associated with alterations of sex hormones but may not be as harmful for bone mass as previously believed. Parity, particularly higher parity, was associated with higher cartilage defects in young women and low cartilage volume in older women indicating an effect of childbearing on the development of OA in women. Adiagram below illustrated the main conclusions from this study.