Vitamin D deficiency

Freaney and McKenna raise the central issue of defining hypovitaminosis D. As they state, the current threshold may be too low and potential beneficiaries of vitamin D supplementation may include those who were previously believed to be replete with vitamin D. In addition to supplementation of groups at risk, fortification of milk would be a step forward, but experience in the United States and Canada has shown wide variations in the vitamin D content of fortified milk so the benefits of this approach would be limited to those who drink sufficient quantities of milk. 2 Nashef and Lamb raise several questions. Anticonvulsant treatment is a risk factor for osteomalacia and osteoporosis and is associated with an increased prevalence of hypovitaminosis D. The amount of vitamin D required to achieve normal serum 25-hydroxyvitamin D concentrations in patients receiving anticonvulsants varies, in one study ranging between 400 IU and 4000 IU daily. 3 The use of enzyme inducing drugs, particularly in high doses and with other drugs, and lack of exposure to sunlight as a result of being housebound or living in an institution are major risk factors for hypovitaminosis D. A strong case can be made for routine supplementation in such subjects, with serum 25-hydroxyvitamin D concentrations being measured to monitor treatment.