NEW YORK (Reuters Health) - Unlike postmenopausal women, premenopausal women who are overweight and lose weight do not put themselves at risk for osteoporosis, a bone-thinning disease, if they are getting enough calcium, researchers report in the Journal of Clinical Nutrition.

Dr. Sue A. Shapses of Rutgers University in New Brunswick, New Jersey, and colleagues studied 44 overweight premenopausal women who were an average of 38 years old and had an average body mass index of 27.7. A body mass index, which is the ratio between weight and height, higher than 25.0 is classified as overweight.

Women were randomly assigned to a normal calcium diet (1 gram daily) or a high calcium diet (1.8 gram daily) during six months of weight loss, or to 1 gram of calcium daily during six months of weight maintenance. Bone mineral density (BMD) and other indications of bone loss were measured periodically during the study period.

The two weight loss groups lost an average of 7.2 percent of body weight. There was no decrease in BMD or increase in bone turnover with either the normal- or high-calcium diet.

The high-calcium group showed a trend towards increased density of the hip bone and increased levels of serum 25-hydroxy vitamin D, an indicator of vitamin D levels.

The total amount of calcium absorbed was adequate in subjects who had normal or high levels of calcium each day, and the amount of calcium absorbed was unchanged by weight loss.

"If young healthy women consume their recommended levels of calcium and consume a multivitamin that includes vitamin D, there is no reason that they can expect to lose bone, even during a weight loss diet (it will be primarily fat tissue), if it is a healthy weight loss," Shapses commented to Reuters Health. "They should not worry that they are putting themselves at risk for osteoporosis."

"We believe the reason for no bone loss is that the high levels of estrogen prior to menopause not only protect bones during weight stable conditions, but also during weight loss, unlike postmenopausal women where we see a decline in their already low levels of estrogen with weight loss, and a decrease in calcium absorption," Shapses explained.

More calcium is recommended for postmenopausal women -- about 1.5 to 1.7 grams per day, along with about 400 IU day of vitamin D, she advised.