Vitamin D and cystic fibrosis

Abstract

Cystic fibrosis (CF) patients suffer from malnutrition and lung infections, both acute and chronic. The majority are also vitamin D insufficient despite vitamin D supplementation. With better medical care the life expectancy for CF patients has increased and so has the prevalence of long-term complications, such as bone disease and CF-related diabetes. Vitamin D insufficiency is associated with bone disease in CF, but evidence that vitamin D supplementation improves bone mineral density in CF patients is missing. The pathophysiology of vitamin D insufficiency in CF is multifactorial. Serum 25-hydroxyvitamin D (s25(OH)D) levels in CF patients fluctuate throughout the year, depending on the amount of UV exposure, with lowest values at the end of the winter. The current European and US guidelines for vitamin D supplementation for CF patients prefer colecalciferol over ergocalciferol, consider age of the patients, endorse individualisation of the supplementation regimen and are mostly consensus based due to lack of CF-specific evidence. In all age groups, s25(OH)D >50 nmol/l (Europe) or s25(OH)D >75 nmol/l (US) should be achieved and maintained. The current literature is missing CF-specific hard evidence on many issues, such as the optimal s25(OH)D level, the relative benefit of colecalciferol vs. ergocalciferol and daily vs. weekly supplementation regimen. The use of UV lamps is a promising alternative, but has so far been ineffective in raising s25(OH)D level in CF patients due to poor adherence with the treatment. In vitro experiments and human descriptive studies indicate that vitamin D might have beneficial immunomodulatory and glucose-lowering effects in CF patients, but a careful approach is to be recommended given the absence of well-designed intervention trials proving causality, safety and clinical relevance of the amplitude of the potential effects. There are a few registered trials currently running or planned to start soon, which address some of these questions.