Vitamin D insufficiency (VDI) contributes to low bone mineral density (BMD) in adults with cystic fibrosis (CF). Vitamin D may improve skeletal/respiratory muscle function and upregulate antimicrobial peptides, improving immunity. This 2-year retrospective study reviewed medical records of 185 adults of mean (SD) age 29 (9) years with CF. Parameters of bone health and the relationship between vitamin D status and forced expiratory volume in 1 s (FEV₁) were investigated.

The subjects (93% white, 17% black) had a mean body mass index (BMI) of 21.2 kg/m²; 70% used multivitamins and 47.6% took vitamin D. VDI was found in 76% of patients (25-hydroxyvitaminD (25(OH)D) <75 nmol/l) and vitamin D deficiency in 23% (25(OH)D <37.5 nmol/l). VDI was associated with race (black>white), lack of vitamin D use and season. The vitamin D status was positively associated with lowest FEV₁, independent of age, gender, BMI and race. BMD was low (lumbar spine T-scores of <−1.0 and <−2.5 in 52% and 10% subjects, respectively), non-significantly associated with vitamin D status. Over 2 years, 27% of subjects had ⩾1 vertebral fracture associated with lower FEV₁ (p<0.001) but not age, BMI, vitamin D or multivitamin supplementation. Multivitamins did not prevent VDI.

Patients with CF with more severe disease (greater fat malabsorption) and lower FEV₁ may have decreased physical activity and sun exposure, all contributing to VDI. Low BMD is associated with vertebral fractures and kyphosis, reducing FEV₁ further. This cross-sectional study could not demonstrate causality between vitamin D status and fractures or FEV₁, but highlights the extent of VDI and skeletal morbidity in adults with CF, calling for improved screening for vitamin D status.

▸ Wolfenden LL, Judd SE, Shah R, et al. Vitamin D and bone health in adults with cystic fibrosis. Clin Endocrinol 2008;69:374–81.