Vitamin D deficiency and its treatment in cystic fibrosis.

Vitamin D deficiency is a common finding in individuals with cystic fibrosis (CF), despite routine supplementation. Hypovitaminosis D is often the result of fat malabsorption, but other contributors include increased latitude, poor nutritional intake, decreased sun exposure, impaired hydroxylation of vitamin D, and non-adherence to the prescribed vitamin D regimen. Vitamin D is critical for calcium homeostasis and optimal skeletal health, and vitamin D deficiency in CF can lead to skeletal complications of osteopenia and osteoporosis. Over time, our understanding of treatment regimens for vitamin D deficiency in CF has evolved, leading to recommendations for higher doses of vitamin D to achieve target levels of circulating 25-hydroxyvitamin D. There is also some evidence that vitamin D deficiency may have non-skeletal consequences such as an increase in pulmonary exacerbations. The exact mechanisms involved in the non-skeletal complications of vitamin D deficiency are not clearly understood, but may involve the innate immune system. Future clinical studies are needed to help address whether vitamin D has a role in CF beyond skeletal health.