Serum vitamin D levels in children with cystic fibrosis

Osteopenia is increasingly recognized in adults with cystic fibrosis (CF), and is potentially related to vitamin D deficiency in both adulthood and childhood. Vitamin D supplements are recommended and prescribed to all pancreatic-insufficient patients. We aimed to ascertain whether vitamin D deficiency in children with CF was prevalent. 25-hydroxyvitamin D (25-OHD) was measured in 290 children attending a specialist pediatric CF clinic for annual assessment. 25-OHD levels were compared with reference values and to other biochemical markers, lung function, and growth. Levels were also analyzed by pancreatic status and by the presence of CF-related liver disease. Median 25-OHD was 65 (range, 9-190) nmol/l. One percent had levels below 15 nmol/l, and 6% had levels less than 25 nmol/l. Levels were lower in adolescents (P < 0.001) and during the "winter" months (P < 0.001). No relationship was found with pancreatic status or liver disease. In conclusion, the majority of children had normal 25-OHD levels. Interpretation is difficult due to a lack of knowledge of optimal levels of 25-OHD required for healthy bone accretion. Lower levels in adolescents may be a precursor to low levels in adulthood, and did not seem to be simply related to poor compliance with supplementation. This may reflect normal physiology.