21st Century Calcium 6 + D Caplets For Bone Health Prevents and treats low calcium and vitamin D levels in your body and is formulated with a highly absorbable form of Calcium as Calcium Carbonate 6 mg along with Vitamin D3 to maintain normal bone health, as Calcium can only reach its full bone-building potential if your body has enough vitamin D, while Vitamin D assists in the absorption of Calcium and helps build and maintain the health of your bones, supports normal bone development and maintenance, and helps support the nervous system, musculoskeletal system, and immune system as part of a wellness-focused lifestyle and diet.