Brisk walking or jogging showed some of the clearest bone benefits for over-40s in a review of 124 trials

Most of us are told at some point that exercise is good for our bones, but the advice is often vague. Which kind of exercise, and how much? A large new analysis in the BMJ pooled 124 randomized trials, involving 18,429 adults aged 40 and over, to rank the options.

Brisk walking or jogging came out as one of the most consistent performers, with benefits at the spine and hip. The analysis also points to a sweet spot of about two to three hours a week, although much of the evidence is less certain than the headline suggests.

Why does bone density matter as we age?

Bones are living tissue that the body constantly breaks down and rebuilds. MedlinePlus explains that osteoporosis is a disease in which your bones become weak and are likely to fracture, and that it develops when more bone is broken down than replaced. That becomes more likely with age, especially for women after menopause.

Bone mineral density, or BMD, is the standard way to measure bone strength. It is usually taken with a special X-ray scan at the lower spine and the hip, including the femoral neck, the narrow top part of the thigh bone near the hip joint. Because osteoporosis rarely causes symptoms until a bone breaks, slowing the loss of density is a common goal.

How did the researchers compare different types of exercise?

The team searched for randomized controlled trials that compared structured exercise with no exercise or with another type of exercise in adults aged 40 to 60 and over 60. They found 124.

They used a network meta-analysis, a method that combines many trials to compare several treatments at once, including pairs that were never tested head to head. They also rated how certain each result was, using an established tool that considers issues such as study quality and consistency.

Which exercise did the most for bone density?

Different parts of the skeleton responded to different activities. For the lower spine, brisk walking or jogging and combined aerobic and resistance exercise probably improve bone density compared with doing nothing. For the femoral neck, brisk walking or jogging and mind-body exercise may provide the greatest benefit. For the hip as a whole, only brisk walking or jogging stood out.

The gains were modest in absolute terms, on the order of a hundredth of a gram per square centimeter. In older adults, where the usual direction is steady loss, holding density steady or nudging it up can still matter.

How much exercise was enough for bone health?

The team also looked at dose. They measured exercise in MET-minutes, which account for both effort and time. One MET is the energy used at rest, so harder activities count for more per minute.

The dose-response relationship was not a straight line. It was generally an inverted U shape, meaning benefits rose with more exercise and then leveled off or dipped. The authors estimate that meaningful benefits might generally be achieved at around 600 MET-minutes a week, equivalent to about 2-3 hours of brisk walking or jogging. For the lower spine, benefits might start at around 400.

Did exercise reduce fractures?

Fractures are what really matter, but fewer trials measured them. In 26 trials with 11,132 participants, mixed aerobic exercise and mind-body exercise may reduce fracture risk, while other types showed no clear effect.

Those fracture results were rated low certainty, which means the true effect could be quite different. That is the part of this study to hold most loosely.

How confident can we be in the bone results?

The analysis is large and limited to randomized trials, which is a strength. But the authors rate much of the evidence as low to moderate certainty, and they describe their conclusions as cautious support for tailoring exercise advice by type and dose. The trials tested many different programs in different groups of people, and bone density is a stand-in for fracture risk rather than the outcome itself.

What does this mean for keeping your bones strong?

If you are over 40 and looking for a practical target, the findings point to regular brisk walking or jogging, adding up to a couple of hours or more across the week. Brisk walking is a lower-impact option for people who find running hard on their joints.

Anyone who already has osteoporosis, has fallen, or has heart or joint problems should talk to a health care provider before starting something new. MedlinePlus notes that osteoporosis is called a “silent” disease because it rarely causes symptoms, so exercise is best seen as one part of protecting bones, alongside checking in with a doctor about bone health.