Two to three hours of brisk walking a week was linked to meaningful bone gains after 40

Design

Bayesian network and dose-response meta-analysis of randomised trials

Population

124 trials, 18,429 adults aged ≥40

Primary outcome

Change in lumbar spine, femoral neck and total hip bone density

Effect

Walking/jogging total hip +0.021 g/cm² (0.005–0.038); mixed aerobic fracture OR 0.29 (0.11–0.78)

A network meta-analysis in the BMJ (9 September) pooled 124 randomised trials with 18,429 adults aged 40 and over to ask which kind and how much exercise protects bone.

Brisk walking or jogging and combined aerobic-resistance training improved lumbar spine density compared with no exercise; walking or jogging and mind-body exercise such as tai chi helped the femoral neck. The dose-response curve was an inverted U, with a clinically meaningful change at about 400 MET-minutes a week for the spine and 600 for the hip — roughly two to three hours of brisk walking. In 26 trials reporting fractures, mixed aerobic exercise (OR 0.29) and mind-body exercise (OR 0.58) were associated with fewer fractures.

The certainty was mostly low to moderate and the fracture analysis rests on small numbers. But the direction is consistent and the prescription is cheap, safe for most and easy to give.

• Recommend brisk walking or jogging, about 2–3 hours a week, to adults over 40 for bone health.
• Combined aerobic and resistance training is a reasonable alternative for the spine.
• Tai chi or similar mind-body exercise may suit frailer patients and may lower fracture risk.
• Exercise supplements, not replaces, drug treatment for established osteoporosis.

Why it matters

It gives a specific dose to replace the vague advice to 'stay active'.

Don't overread it

The fracture reductions are low-certainty estimates from 26 trials; the firmer finding is on bone density.

The statistics, in plain English

Changes of about 0.01–0.02 g/cm² in bone density are small in absolute terms but comparable with the yearly loss after menopause. The fracture odds ratios have wide credible intervals (0.11 to 0.78) and low certainty, so they suggest rather than prove fewer fractures.

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