One of the main focuses of lifestyle modification for the prevention of osteoporosis and osteoporotic fractures in Japan is improvement in dietary calcium intake. However, virtually no randomized controlled trial to assess the preventive effects of administration of calcium on the risk of fractures has been conducted in Japan. In this study, we reviewed all the scientific papers currently available from medical literature databases to propose evidence-based recommendations on the preventive procedures for osteoporosis. The result of the present systematic review gives the evidence showing that calcium supplementation or optimal dietary calcium intake increases bone density in childhood and adolescence and reduces the risk of fracture due to osteoporosis in the elderly people regardless of the gender. The evidence also supports the current health policy guiding the elderly to increase their dietary calcium intake in daily life.