Doctors asked girls whose daily diets had less than 220 mg of magnesium to take 300 mg of magnesium oxide in two 150 mg capsules per day or a placebo for 12 months. At the end of the study, compared to placebo, girls who had taken magnesium had significantly increased bone mineral content (BMC) of the hip.
Doctors also noted an increase—though not statistically significant—in BMC of the lumbar spine and concluded that magnesium safely improved BMC of the hip without side effects.