evidence: Vitamin D is important for building and maintaining strong bones, as well as regulating calcium and phosphate ion levels in the body. People can obtain vitamin D from food and sun exposure. However, vitamin D supplements may be recommended for people who have difficulty meeting their needs through natural sources. Two groups at high risk of vitamin D deficiency are breastfed infants, as human milk doesn’t contain enough vitamin D, as well as the elderly, because the body’s ability to store and make vitamin D diminishes with age.