Vitamin D and bone health in adults with cystic fibrosis

Abstract

Background: Cystic fibrosis (CF) patients have chronic pancreatic insufficiency leading to malabsorption of fat-soluble vitamins, including vitamin D which can contribute to poor skeletal health and respiratory function.

Objective: This study evaluated the prevalence of vitamin D insufficiency and its impact on bone and respiratory health in adults with CF.

Design and measurements: This was a retrospective study in which data were collected from medical records over a 2-year period. Data included patient demographics, lung function, biochemical data, bone mineral densities, X-rays and ascertainment of use of vitamin supplements. Data were collected from medical records at a single accredited CF Center. Serum 25-hydroxyvitamin D [25(OH)D] levels and bone mineral density studies were also collected.

Patients: A total of 185 adults with CF were identified with a mean age of 29 +/- 9 years.

Results: The prevalence of vitamin D insufficiency [25(OH)D < 75 nmol/l] was 76%. Mean serum 25(OH)D concentrations were 58.8 +/- 30 nmol/l. Use of specific vitamin D supplementation was protective against vitamin D insufficiency whereas use of multivitamins was not. There was a small, but significant, positive association between serum 25(OH)D and FEV(1) per cent predicted after controlling for age, gender, BMI and race (R(2) = 0.30, P < 0.001). A high prevalence (27%) of vertebral fractures was detected on lateral chest X-ray.

Conclusions: The prevalence of vitamin D insufficiency and poor skeletal health is high in the US CF population. Vitamin D status appears to be positively associated with lung function. Prospective studies to examine the impact of correction of vitamin D insufficiency on skeletal and lung health in adult CF are warranted.

Fig. 1

Lowest annual FEV₁% compared to blood 25-hydroxyvitamin D concentrations in adult subjects with cystic fibrosis. The lowest annual FEV₁% predicted annually for each subject was plotted vs.25-hydroxyvitamin D (nmol/l) over a two year period (2004–05). There is a positive correlation between FEV₁% predicted and 25-hydroxyvitamin D (β = 0·25, P = 0·05) when controlling for gender, race, age and BMI.

Fig. 2

Seasonal variation of 25-hydroxyvitamin D [25(OH)D] in adult subjects with cystic fibrosis. The mean 25(OH)D levels (nmol/l) of adult CF subjects from each season over the 2-year period were compared using one-way ANOVA. Winter months had the lowest levels (44 ± 24) compared to the spring (59 ± 29), summer (69 ± 27) and fall (70 ± 33) (P < 0·0001).