NOW Calcium/Magnesium Citrate with Vitamin D Powder is an optimal bone structure support formula designed by NOW's certified nutritionists. It contains key nutrients that play essential roles in bone metabolism. The citrate forms of calcium and magnesium are highly absorbable and support not only strong bones and teeth but muscle and nerve function as well. Vitamin D is included for its synergism with calcium and magnesium and its role in the maintenance of mineral homeostasis and bone structure.