Bone Builder MBD is an excellent, comprehensive bone support formula that features the same calcium-rich MCHC found in original Bone Builder, but with other bone-nourishing nutrients. Features a 2:1 ratio of calcium to magnesium for optimal absorption. Magnesium plays important roles in bone metabolism, with over one-half of the total body stores of magnesium found in bone tissue. Boron is a trace mineral that may support bone health through its involvement in vitamin D and estrogen metabolism. Vitamin D is an essential nutrient that helps stimulate calcium absorption and regulate calcium and phosphorus levels in the body.