Cholecalciferol significantly increases 25-hydroxyvitamin D concentrations in adults with cystic fibrosis.

BACKGROUND: Vitamin D deficiency is increasingly being recognized and treated in patients with cystic fibrosis, although the treatment guidelines are not proven and the effectiveness of vitamin D preparations is untested.

OBJECTIVES: The aims of this study were to determine the prevalence of 25-hydroxyvitamin D [25(OH)D] deficiency in a large cohort of adults with cystic fibrosis and to evaluate the effectiveness of supplementation with cholecalciferol.

DESIGN: In this retrospective cohort design, baseline 25(OH)D concentrations were measured, and the effects of clinical interventions that involved either counseling on compliance or increasing supplemental cholecalciferol on serum 25(OH)D concentrations in those subjects with baseline concentrations <or= 50 nmol/L were evaluated.

RESULTS: Of 360 adults with cystic fibrosis, 249 (69%) had baseline 25(OH)D concentrations <or= 50 nmol/L, despite similar levels of supplementation. The lowest 25(OH)D concentrations were seen in younger subjects who had lower body mass indexes and less pulmonary function. Serum 25(OH)D concentrations increased significantly (P<0.0001)--from 35.5 +/- 10.1 to 62.5 +/- 19.1 nmol/L--in 92% of the subjects after the intervention. The subjects with baseline 25(OH)D concentrations < 25 nmol/L had the largest increase in serum 25(OH)D (P=0.02).

CONCLUSIONS: A significant proportion of adults with cystic fibrosis have serum 25(OH)D concentrations <or= 50 nmol/L. Cholecalciferol increases serum 25(OH)D concentrations significantly, and the maximum response occurs in persons with the lowest baseline concentrations.