A 2% swing: exercise protects spine bone density after menopause

Low bone mineral density at the lumbar spine is a major public health problem among postmenopausal women, because the spine is one of the sites where bone thins fastest once oestrogen falls. Whether exercise can genuinely slow or reverse that loss has been studied many times, but individual trials are often small and their results vary. This analysis set out to answer the question with more power than any single trial could, by pooling the raw data from many studies into one dataset and testing whether exercisers really do end up with better spine bone density than controls.

The researchers requested individual patient data from a previously built database of trials on exercise and bone mineral density, which included both randomised and nonrandomised studies. They assembled 13 trials with 699 postmenopausal women in total, of whom 355 were in exercise groups and 344 were controls. Rather than comparing published summary figures, they analysed each woman's own before and after measurements of lumbar spine bone mineral density, using two-way analysis of variance with pairwise comparisons to test whether the change over time differed between the exercise and control groups.

There was a statistically significant interaction between time and group, meaning the two groups moved in different directions. Women in the exercise groups gained bone, with a mean change of 0.005 g/cm², while women in the control groups lost bone, with a mean change of minus 0.007 g/cm². Both changes were statistically significant in their own right. Expressed in relative terms, the exercisers improved by about 1% and the controls declined by about 1%, so the overall benefit of exercising worked out at roughly 2% in lumbar spine bone mineral density.

Pooling individual patient data is a stronger approach than combining published averages, so this analysis adds weight to the long-standing view that exercise helps preserve bone in postmenopausal women. It confirms the direction of earlier findings while putting a concrete, if modest, number on the benefit. What it cannot settle from this abstract is which type, intensity or amount of exercise works best, whether the effect grows or fades over longer periods, and whether a roughly 2% difference in spine density translates into fewer fractures, which is the outcome that ultimately matters.

For a woman past menopause, this is a reason to view regular exercise as bone maintenance as much as fitness. The striking detail is not the size of the gain, which at about 1% is modest, but the contrast with the controls, who lost about 1% over the same trials simply by carrying on as usual. In other words, doing nothing was not neutral here. The evidence does not say which workout is best for bone, only that women who exercised held onto spine density that their non-exercising counterparts gave up.