Ester-C 500mg is a source of both elemental calcium and vitamin C in its non-acidic form. Calcium provides support to the bones, teeth, as well as proper heart and muscle functioning. Vitamin C provides support to the immune system, improves skin texture and mops up harmful free radicals in the system. It also contains bioflavonoids obtained from citrus fruits such as tangerine, sweet orange, lime, and lemon. These metabolites assist vitamin C's support to the immune system.