Bone mineral changes in obese women during a moderate weight loss with andwithout calcium supplementation

A significant relationship between body weight (BW) and bone mass (BM) has been established previously. A diet-induced weight loss is accompanied by a significant decrease in bone mineral density (BMD) and total body bone min eral (TBBM), but the underlying mechanisms are not clarified. Sixty-two obe se women were included in the study. Dual-energy X-ray absorptiometry (DXA) and measurements of a series of calcium-regulating hormones and biochemica l markers of bone turnover were performed at baseline and after 1 month and 3 months on a low calorie diet. Thirty of the women were randomized to a d aily supplement of 1 g of calcium. After an additional 3 months without die tary prescriptions or calcium supplements, a subgroup of 48 subjects (24 fr om each group) were scanned again using DXA. There was a significant decrea se in TBBM after 1 month and 3 months. A similar pattern was observed in th e bone mineral content (BMC) of the lumbar spine in the patients who did no t receive a calcium supplement, whereas no changes occurred in the suppleme nted group. The initial calcium supplementation seemed to protect against b one loss in the lumbar spine but not in the TBBM. In the nonsupplemented gr oup, a statistically significant inverse correlation was found between the calcium/creatinine ratio in the morning urine and the changes in BMC of the lumbar spine. Such a relationship was not seen in the calcium-supplemented group. In the nonsupplemented group, no significant biochemical changes we re observed, whereas a significant decrease in serum parathyroid hormone (P TH) was seen in the calcium-supplemented group. This might explain some of the protective effects of calcium supplementation on trabecular bone mass. We conclude that a diet-induced weight loss is accompanied by a generalized bone loss, which probably is explained mainly by a reduced mechanical stra in on the skeleton. This loss can be partly inhibited by a high calcium int ake. Therefore, a calcium supplementation should be recommended during weig ht loss, even if the diet contains the officially recommended amounts of ca lcium.