Meta-analysis of walking for preservation of bone mineral density in postmenopausal women.

Whilst exercise is recommended for optimum bone health in adult women, there are few systematic reviews of the efficacy of walking as singular exercise therapy for postmenopausal bone loss. The aim of this study was to assess the effects of prescribed walking programmes on bone mineral density (BMD) at the hip and spine in postmenopausal women and to determine if effects are modified by variations in protocol design. We undertook a systematic review and meta-analysis of randomised (RCTs) and non-randomised controlled trials. Electronic bibliographic databases, key journals and reference lists of reviews and articles were searched to identify studies for inclusion. Randomised and non-randomised controlled trials assessing the effects of walking on lumbar spine, femoral neck and total hip BMD, measured by radiographic techniques, among sedentary postmenopausal women were eligible for inclusion. Two independent reviewers assessed studies for eligibility. Reported absolute BMD outcomes were combined in the analysis. Weighted mean differences (WMD) were calculated using a fixed and random-effects models. Heterogeneity among trials was examined using the Q statistic and I2 methods. Potential publication bias was assessed through funnel plot inspection. Assessment of trial quality was also performed using the widely used instrument devised by Jadad et al. [Jadad AR, Moore RA, Carroll D, Jenkinson C, Reynolds DJM, Gavaghan DJ, et al. Assessing the quality of reports of randomized clinical trials: Is blinding necessary? Cont Clin Trials 1996; 17:1-12]. Eight trials were eligible for inclusion. Treatment duration ranged from 6 to 24 months. All eight trials reported BMD data at the lumbar spine following walking interventions among postmenopausal women. Meta-analysis showed no significant change in BMD at this site [WMD (fixed-effect) 0.007 g/cm2 95% CI (-0.001 to 0.016); P=0.09)]. BMD data at the femoral neck were available from five trials among postmenopausal women. Results were inconsistent (I2=51.4%) in showing a positive effect of walking on BMD at this site [WMD (random-effects) 0.014 g/cm2 95% CI (0.000 to 0.028); P=0.05). Insufficient data were available for meta-analysis of the total hip site. Funnel plots showed some asymmetry for negative lumbar spine BMD outcomes. Trial quality scores ranged from 0 to 3 from the Jadad scale of 0 to 5. We conclude that regular walking has no significant effect on preservation of BMD at the spine in postmenopausal women, whilst significant positive effects at femoral neck are evident. However, diverse methodological and reporting discrepancies are apparent in the published trials on which these conclusions are based. Other forms of exercise that provide greater targeted skeletal loading may be required to preserve bone mineral density in this population.