Vitamin D deficiency is more common than realized. It is making a resurgence in neonates and is common in black patients and older adults. Vitamin D deficiency not only causes generalized muscle weakness, muscle aches, and bone aches and pains but also can precipitate and exacerbate osteoporosis and cause osteomalacia. Although the kidney plays a critical role in producing 1,25-dihydroxyvitamin D, which is important for regulating calcium, phosphorus, and bone metabolism, it is now recognized that a wide variety of other tissues have the enzymatic machinery to produce 1,25-dihydroxyvitamin D. Vitamin D receptors are common in most tissues in the body, and the new revelation that many tissues produce 1,25-dihydroxyvitamin D suggests a new important role for this hormone in helping to maintain good health throughout life.
Vitamin D, Skin and Bone Research Laboratory; Section of Endocrinology, Diabetes, and Nutrition; Departments of Medicine, Dermatology and Biophysics and Physiology; Boston University Medical Center, Boston, Massachusetts, USA.
Correspondence to Michael F. Holick, Ph.D., M.D., Boston University School of Medicine 715 Albany Street, Boston, MA 02118, USA; e-mail: firstname.lastname@example.org