Researchers from Rutgers University in New Brunswick, New Jersey, recruited 44 overweight pre-menopausal women, average age 38, to take calcium while dieting or while maintaining weight for six months. The dieters took a normal amount of calcium—1,000 mg per day—or a high dose of 1,800 mg per day, while non-dieters took 1,000 mg of calcium per day. Scientists noted that people typically lose bone density when losing weight, but that no bone studies exist on overweight pre-menopausal women who diet.
Women in the normal and high calcium diet groups lost an average of 7.2% of body weight with no significant decrease in bone mineral density (BMD, a measure of bone strength) and researchers found no signs in the blood that the dieters were losing bone. Doctors also found that the dieters were able to absorb an adequate total amount of calcium from their diets and supplements and concluded that taking calcium while losing weight helps maintain healthy bones.
In research funded by the U.S. Department of Defense, doctors studied bone stress fractures in 5,201 female Navy recruits aged 17 to 35 from 2002 through 2006. Recruits took 2,000 mg of calcium plus 800 IU of vitamin D per day or a placebo during the eight week basic training period. Over the study period, 170 recruits in the placebo group suffered stress fractures compared to 136 recruits in the calcium/vitamin D group, meaning that calcium and vitamin D reduced risk for stress fractures by 20%.
Researchers noted that recruits who had a history of regular exercise had lower risk for fractures than did those who had not exercised regularly and that those who smoked had higher fracture risk than non-smokers. Doctors were not expecting to find such a significant bone benefit in such a short period of time and concluded that calcium and vitamin D reduced risk for stress fractures.