Cal-Mag SAPCalcium, magnesium, and vitamin D3 for bone health (based on science) Bone mass and vitamin D synthesis decline with aging and inactivity in women and men. Reducing bone loss delays the onset of weakness, thereby decreasing the risk of fracture. Maximum bone mass is determined by genetics, body weight, weight bearing activity and the intake of nutrients composing the bone matrix and or regulating its metabolism. Adequate calcium intake is important