Bone remodelling is well known to be heavily influenced by the load placed upon it. Heavier people, for example, are more likely to have heavier bones. But how does weight loss impact bone density?

Laurie Milliken and colleagues at the University of Massachusetts, Boston, reported that changes in body weight account for a substantial change in bone density recorded in post-menopausal women.

“These findings demonstrate that in this population of postmenopausal women, changes in body composition are more important than the current public health messages regarding preserving bone may reflect,” said Milliken.

For four years the researchers followed 167 post-menopausal women taking part in the Bone Estrogen Strength Training study. Correcting for other factors such as level of exercise, use of hormone replacement therapy and taking supplemental calcium, Milliken and colleagues found that 6%-32% of the change in bone mineral density (BMD) could be accounted for by change in body mass, with weight loss leading to lower BMD.

“These findings confirm the ‘bone loading’ role of body weight. However, it may add confusion for those who are trying to reduce the likelihood of developing osteoporosis, especially those who are also trying to prevent heart disease and Type II diabetes. The public health messages for heart disease and diabetes are to lose weight but that advice may be counterproductive for bone,” said Milliken.

That sentiment was echoed by Dr. Bryan Whelan and colleagues at Cork University Hospital, Ireland. In a study of over 22,000 subjects, they found that there was a direct correlation between weight and bone mineral density at the hip, spine, and thigh bone.

“Our main finding was that setting a weight cut-off in postmenopausal women and men over 50 is a simple way of determining if they are likely to have osteoporosis or not,” said Whelan.

Those cut-offs are 72kg for women 81 kg for men. The research suggests that people should be mindful of not dieting to a level where their weight falls below these limits. “In this age, when there is such an emphasis on being thin and losing weight, it must be said that a good balance-not too thin, not too heavy-is still best because there are drawbacks to being too light, said Whelan.

http://www.osteofound.org