Vitamin D and Its Non-Classic Roles in Cystic Fibrosis

Vitamin D deficiency is common in cystic fibrosis (CF) and persists despite relatively high doses of ergocalciferol, vitamin D2. Replacement has traditionally been focused upon maintenance of calcium and phosphorus homeostasis and bone health. However, non-classic roles of vitamin D have become increasingly recognized and the contribution of vitamin D deficiency to non-bone disorders has become apparent. Vitamin D deficiency has been associated with increased risk of a variety of cancers, autoimmune diseases such as Type 1 diabetes and multiple sclerosis, Type 2 diabetes, tuberculosis, and myopathy. The connection between vitamin D and these disease states likely reflects vitamin D's role as a transcriptional regulator: it participates in cell cycle regulation and in the innate immune system mediates cathelicidin production following activation of toll-like receptors.One hallmark of CF is pulmonary hyper-inflammation with recurrent infections. Additionally, malnutrition and decreased lean muscle mass threaten pulmonary function in CF. While vitamin D and its relation to bone has been explored in CF, the role of vitamin D in inflammation, lean body mass and strength, and pulmonary muscle strength has not been investigated. Moreover, vitamin D replacement has traditionally been with ergocalciferol, vitamin D2. Vitamin D3, cholecalciferol, has a longer half-life and is considered more potent. Thus, cholecalciferol treatment of children and young adults with CF and vitamin D deficiency may be useful for attaining normal vitamin D status and for exploring the impact of vitamin D upon lean body mass, pulmonary muscle strength, and inflammation.