Exercise's small bone gains may cut fracture risk by 11%

After menopause, bone loss accelerates, and low bone mineral density with the fractures that follow is a major public health problem in postmenopausal women. Hip and spine fractures in particular can permanently change a person's independence. Exercise is widely promoted as bone medicine, but individual trials are small and their results scatter, so it has been hard to say how much benefit a previously inactive woman can really expect. This analysis pooled the randomised evidence to test whether ground reaction exercise such as walking, and joint reaction exercise such as strength training, genuinely improve bone density at the femoral neck and lumbar spine.

The researchers pooled randomised controlled trials lasting at least 24 weeks that compared exercise with a control group in postmenopausal women who were not regularly active. Studies were located through six electronic databases, cross-referencing, hand searching and expert review, covering published and unpublished work in any language since 1989. Standardised effect sizes were calculated for each bone density result and combined using random-effects models, giving 28 results for the femoral neck from 1632 participants and 28 for the lumbar spine from 1504 participants. Further analyses examined whether characteristics of the trials or participants changed the results.

Exercise groups improved bone density more than controls at both sites, though the gains were small: a standardised effect of 0.288 at the femoral neck and 0.179 at the lumbar spine, with the spine result only just reaching significance. Translated clinically, the authors estimated these changes would reduce the 20-year relative risk of osteoporotic fracture at any site by approximately 11% for the femoral neck and 10% for the spine, with a number needed to treat of 6 at both sites. None of the subgroup analyses were statistically significant, although associations with 20 different predictors were flagged as worth further study.

This confirms the broad view that weight-bearing and resistance exercise protect bone in postmenopausal women, and it extends that view by attaching a clinical estimate to what look like tiny density changes. The included trials disagreed with each other considerably, and none of the subgroup comparisons could identify which exercise ingredients matter most, so the recipe question stays open. The fracture risk reductions are modelled from bone density change rather than observed fracture counts, which the authors acknowledge by calling for further well-designed randomised trials.

For women past menopause, this is a reason to view regular walking-style activity and strength work as a genuine, if modest, investment in the skeleton. The gains accrued over at least 24 weeks in women who started out inactive, so it describes a sustained habit rather than a quick fix. It is also worth holding the numbers lightly: the fracture estimates are projections from density changes, useful for sizing the stakes but not the same as counted fractures prevented.