Prospective Intervention Study on Vitamin D in Patients With Cystic Fibrosis

5-month Pilot Intervention Study on Vitamin D in Patients With Cystic Fibrosis

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.

Inclusion Criteria:

• Established diagnosis of cystic fibrosis
• Age 6 years and more
• Serum 25-hydroxy vitamin D concentration at the latest visit < 75 nmol/L

Exclusion Criteria:

• Pregnancy or lactation
• Established diagnosis of CF-related diabetes
• CF-related liver disease
• Status post transplantation (lung, liver or other)
• Long-term corticosteroid treatment per os
• Hypercalcaemia or kidney stones
• Use of tanning beds more often than once a month
• At inclusion, plans to travel to a sunny location for more than 1 week during the study period
• Any known disorders of the endocrine system affecting vitamin D metabolism (hyperparathyroidism, malignancy, advanced renal disease)
• Inclusion into another study testing immunomodulatory substances