Calcium and vitamin D: skeletal and extraskeletal health

Vitamin D is known for its role in calcium homeostasis for optimal skeletal health. It was previously believed that only elderly or hospitalized patients were at risk for vitamin D insufficiency, but many people in the general US population have insufficient levels of 25-hydroxyvitamin D (25D). According to the Third National Health and Nutrition Examination Survey, 61% of white and 91% of black Americans suffer from vitamin D insufficiency (25D < 32 ng/mL). Recent studies have demonstrated that a minimum 25(OH)D level of 32 ng/mL is necessary for optimal protection from fracture and intestinal absorption of calcium. Recently, vitamin D has been recognized as important for extraskeletal functions such as immune function, cancer prevention, and hypertension prevention. We review the role of vitamin D in skeletal health and present data on vitamin D in other extraskeletal diseases, with special emphasis on the rheumatology patient.