Adding exercise to hormone therapy did not measurably boost bone density

Bone is a living tissue that responds to mechanical loading, but there is evidence that it needs an adequate anabolic hormonal environment to sense and respond to that loading properly. That raises a practical question for women using hormone therapy: does adding exercise on top of the therapy build more bone than the therapy alone? If loading and hormones genuinely work together, the combination should beat either one by itself. This review set out to test exactly that, focusing on bone mineral density at the lumbar spine and femoral neck, the two sites that matter most for fracture risk assessment in later life.

The researchers searched 6 electronic databases according to the PRISMA statement, covering the literature up to April 28, 2021. They included only controlled trials longer than 6 months that had three separate arms: hormone therapy alone, exercise alone, and hormone therapy plus exercise. Trials involving other drugs or diseases with meaningful effects on bone metabolism were excluded, so the participants were healthy women. The data were combined in a random-effects meta-analysis, with standardised mean differences in bone mineral density changes at the lumbar spine and femoral neck as the outcome measures. The search identified 6 eligible studies with 585 participants between them.

The combined hormone therapy plus exercise groups showed somewhat larger bone density effects than hormone therapy alone, with a standardised mean difference of 0.19 at the lumbar spine and 0.18 at the femoral neck. However, neither difference was statistically significant: the ranges around both estimates included the possibility of no effect at all. In plainer terms, the trend favoured the combination but the evidence could not confirm it. The trials agreed with each other to a reasonable degree, with low disagreement for the femoral neck results and moderate disagreement for the lumbar spine results.

The finding complicates the intuitive idea that hormones and mechanical loading should stack neatly on top of each other. The authors largely attribute the null result to the varying hormone therapy regimens and hormonal status across the included trials, and they note that synergistic or additive effects between hormones and mechanical stimulation would only be expected when hormones are genuinely insufficient to begin with. That leaves the central question open rather than answered. They call for future trials to account more carefully for baseline endogenous oestrogen production and for hormone therapy dosing, so that any real interaction is not washed out by mismatched participants.

For a woman using hormone therapy, this is a reason not to expect exercise to deliver a measurable bonus to bone density on top of what the therapy provides, at least based on the trials pooled here. It is equally a reason not to read too much into the null: the trend favoured the combination, the trials were few, and the mixed hormone doses may have hidden a real effect. The most useful insight may be the conditional one: any synergy between hormones and loading likely depends on a woman's hormonal starting point, which is precisely what these trials did not control well.