The vast majority of Cystic Fibrosis (CF) patients worldwide are vitamin D insufficient.
There is no evidence of benefit of vitamin D supplementation for CF patients yet. However,
descriptive cross-sectional studies suggest that vitamin D might be beneficial with respect
to bone health, as well as to the newly described "non-classical" functions of vitamin D such
as the potential anti-diabetic and immunomodulatory effects. To prove causation, and to
determine which serum vitamin D concentration is optimal for CF patients, vitamin D
supplementation interventional studies are needed, such as our trial.