Strategies to address the long-term maintenance of bone mineral density in younger women

Long-term maintenance of bone mineral density (BMD) in premenopausal women is critical to preventing osteoporosis and osteoporotic fractures. This thesis aimed to investigate potential strategies to optimise long-term bone health in younger women in a cohort of women who 12 years previously had participated in a 2-year randomised controlled trial (RCT) of an osteoporosis education intervention. In the original trial, women were randomised at baseline to receive group education (the Osteoporosis Prevention and Self-management course (OPSMC)) or an information leaflet. All women also received individualised feedback of either being or not being at higher risk of fracture in later life (high and normal risk groups). The risk was based on BMD measured by Dual-energy X-ray absorptiometry (DXA) according to whether or not each participant's mean T-score at spine and hip was less than 0 (high and normal risk groups, respectively). For this thesis, we performed a further 10-year follow-up, i.e. 12 years from baseline of the original RCT. We measured osteoporosis knowledge, self-efficacy, BMD at the femoral neck (FN) and lumbar spine (LS); calcium intake and calcium supplement use, physical activity and smoking status as in the original RCT. In addition, we measured serum 25-hydroxyvitamin D (25(OH)D), lower limb muscle strength (LMS), timed up and go test (TUG), functional reach test (FRT), lateral reach test (LRT) and step test (ST); total physical activity (accelerometer counts/minute of wear time), and time spent sedentary, in light and moderate-to-vigorous physical activity (MVPA). Longitudinal data were used to investigate the long-term effects for the RCT interventions on BMD and osteoporosis preventive behaviours. Cross-sectional data were used to examine associations between the modifiable factors of vitamin D levels, LMS and physical activity and BMD and balance measures. Key findings were: Longitudinal data: 1. From baseline to 12 years, neither feedback of high fracture risk nor the OPSMC had an effect on the change in osteoporosis knowledge or self-efficacy. 2. From 2 to 12 years, the high fracture risk group had a smaller decrease in FN BMD (˜í‚â§=0.023 (95% CI: 0.005-0.042) g/cm¬¨‚â§) but similar LS BMD change as the normal risk group. They also had a more favourable pattern of smoking behaviour change and were more likely to use calcium supplements and be recent users of vitamin D supplements. The OPSMC group had a more favourable pattern of smoking behaviour change compared to the leaflet group. Cross-sectional data at 12 years: 3. There were significant cut-points for associations of 25(OH)D levels with FN BMD, LS BMD, TUG, ST, FRT and LMS (ranging from 29-33 nmol/L) but not LRT. Below these cut-points, there were beneficial associations between higher 25(OH)D level and each outcome while above the cut-points there were no beneficial associations. 4. Weaker LMS was associated with poorer performance on all balance tests. Significant cut-points of LMS were identified for all balance tests (29-50 kg) but excepting ST, these did not persist after excluding potentially influential data points. 5. Total physical activity was beneficially associated with FN BMD, LMS and TUG. MVPA was also beneficially associated with FN BMD, LMS, ST and TUG, and these associations (except for FN BMD) persisted after further adjusting for sedentary time. Sedentary time was detrimentally associated with TUG but not after further adjustment for MVPA. In conclusion, feedback of high fracture risk to younger women was associated with long-term improvements in osteoporosis preventive behaviours and attenuated FN BMD loss and could be considered as a strategy to improve long-term bone health and prevent osteoporosis. Furthermore, we identified other potential strategies for maintaining BMD and balance in middle-aged women, namely: ‚Äö Maintaining adequate serum 25(OH)D noting that the current cut-off defining vitamin D deficiency of 50 nmol/L may be higher than needed for some musculoskeletal outcomes but appears warranted overall. ‚Äö Improving LMS. ‚Äö Increasing time spent in MVPA.