Everyday activities such as walking and housework may be good for the heart, but don't do much for the bones.
Researchers at Johns Hopkins University have studied a group of people aged 55 to 75 who had higher than average blood pressure, but were otherwise healthy. They measured their aerobic fitness, muscle strength and abdominal fat, to see how these were linked to bone density.

Aerobic fitness and doing light exercise did nothing to increase bone density and so avoid osteoporosis. But those with high muscle strength tended to have higher bone density. So, too, did those who were slightly overweight, with a concentration of fat around the abdomen. Having this kind of fat is generally thought to be a risk for heart disease -so it's intriguing to find that it has its healthy side, by protecting bone density.

The researchers obviously can't recommend gaining weight as a way of reducing osteoporosis risk. But they would like to find out how overweight people can lose some weight, while retaining some of the bone density advantages of abdominal fat. Carrying extra body weight strengthens bone by increasing the force on it. Doing vigorous exercise is another way of strengthening bone.