The Role of Vitamin D in the Prevention and Treatment of Osteoporosis

Abstract

Vitamin D is essential for preventing and treating osteoporosis. Vitamin D enhances intestinal calcium absorption to help maintain blood calcium concentrations, necessary for bone mineralization and for muscle and nerve function. Vitamin D is metabolized to 25-hydroxyvitamin D (25OHD) in the liver and to the active form, 1,25-dihydroxyvitamin D [1,25(OH)2D] in the kidney. Inadequate vitamin D status contributes to increased bone turnover, secondary hyperparathyroidism, bone loss, fractures, muscle weakness, osteomalacia, and rickets in children. Vitamin D is synthesized in the skin upon exposure to sunlight. It is also found naturally in some foods and is present in fortified foods, in nonprescription supplements containing other vitamins or calcium, and as pure vitamin D in prescription and nonprescription forms. The concept of vitamin D adequacy has evolved well beyond the need for vitamin D for preventing rickets. Recommendations for vitamin D intake were increased in 1997 but continue to be debated. The best measure of vitamin D status is serum 25OHD, and recent studies suggest this should be at least 32 ng/mL. Many people fall short of this. Risks for poor vitamin D status include advanced age, minimal sun exposure, mal-absorption, and darkly pigmented skin. However, recent work suggests that many otherwise healthy individuals are inadequate in vitamin D. Although best known for its role in skeletal health, other roles for vitamin D in cancer, immunologic disease, and other aspects of health are being explored. Greater understanding of its role in skeletal health and overall well-being, and better avenues for assuring vitamin D adequacy for all people, are needed.