Introduction
Vitamin D promotes calcium absorption and regulates serum calcium and phosphorus concentration to maintain normal bone health (Morris 2005). Although vitamin D can be produced en- dogenously in the skin under sunlight, the exposure to ultraviolet light also poses skin cancer risk (American Cancer Society 2009a). Public awareness of the negative effects of sun exposure and the use of effective means of skin protection from sun exposure (American Cancer Society 2009b) may have had certain unintended effects on vitamin D status, contributing to an increased dietary vitamin D need. In addition, people who have limited sunlight exposure in winter and in northern latitude also are at high risk of vitamin D deficiency. Three quarters of U.S. teens and adults are deficient in vitamin D, and such deficiency is associated with osteomala- cia (weak muscles and bones), reduced immune functions, and increased inflammation (Lite 2009).
The recently released Dietary Reference Intakes for calcium and vitamin D increased the recommended daily intake of vitamin D for children and adults from 200 to 600 IU a day, and from 600 to
800 IU a day for elder people. The safe upper limit on daily intake
Introduction
Vitamin D promotes calcium absorption and regulates serum calcium and phosphorus concentration to maintain normal bone health (Morris 2005). Although vitamin D can be produced en- dogenously in the skin under sunlight, the exposure to ultraviolet light also poses skin cancer risk (American Cancer Society 2009a). Public awareness of the negative effects of sun exposure and the use of effective means of skin protection from sun exposure (American Cancer Society 2009b) may have had certain unintended effects on vitamin D status, contributing to an increased dietary vitamin D need. In addition, people who have limited sunlight exposure in winter and in northern latitude also are at high risk of vitamin D deficiency. Three quarters of U.S. teens and adults are deficient in vitamin D, and such deficiency is associated with osteomala- cia (weak muscles and bones), reduced immune functions, and increased inflammation (Lite 2009).
The recently released Dietary Reference Intakes for calcium and vitamin D increased the recommended daily intake of vitamin D for children and adults from 200 to 600 IU a day, and from 600 to
800 IU a day for elder people. The safe upper limit on daily intake
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