Obese older adults who shed pounds also tend to lose bone mass, even if they exercise regularly. It's known that weight loss, in young and old alike, can be accompanied by a dip in bone density, but researchers have hoped that this could be prevented with exercise, which generally helps build bone mass. In the current study American researchers randomly assigned 27 older adults to one of two groups. In one, participants cut calories and practiced a supervised exercise regimen three times per week; those in the other group maintained their normal lifestyle. All of the men and women were obese and physically frail at the study's start. Those in the exercise group learned to perform a combination of aerobic activity, stretching, balance exercises and strength conditioning. It was found that one year later, people in the diet-and-exercise group had lost 10 percent of their initial weight, on average, while those in the comparison group had typically maintained their weight. But the researchers found a similar pattern with bone density: while bone mass in the hip area held steady in the comparison group, it declined by 2 percent to 3 percent in the weight-loss group. Obese older adults who lost weight through diet and exercise showed a decline in bone mass at the hip - despite a supervised regimen of aerobic and strengthening exercises. Still, the significance of the bone loss - including whether it raises the risk of osteoporosis - is not clear. One reason is that obese adults generally have high bone mass to begin with. It is also possible that the beneficial effects of weight loss on physical function could outweigh this potential adverse effect on bone. It's not entirely surprising that exercise failed to completely prevent bone loss. The exercise regimen they used was designed to improve the participants' physical function, and not specifically to build bone mass. In addition, blood tests showed that the weight-loss group's vitamin D levels tended to be less than optimal. Vitamin D, along with calcium, is needed for maintaining healthy bones. The researchers recommended that older adults who are trying to lose weight be sure to get plenty of calcium and vitamin D - at least 1,000 IU of vitamin D and 1,200 to 1,500 milligram of calcium per day, along with regular exercise. Exercise and weight loss may, for instance, improve frailty and reduce older adults' risk of falls, which, in theory, could prevent more bone fractures. However, more research is needed to answer this question.
Journal of Clinical Endocrinology and Metabolism
June 2008