Vitamin D deficiency as a risk factor for cystic fibrosis-related diabetes in the Scandinavian Cystic Fibrosis Nutritional Study

Aims/hypothesis Many cystic fibrosis patients are vitamin D-insufficient. Cystic fibrosis-related diabetes is a major complication of cystic fibrosis. The literature suggests that vitamin D might possess certain glucose-lowering properties. We aimed to assess the relationship between vitamin D and cystic fibrosis-related glucose intolerance. Methods We enrolled 898 cystic fibrosis patients from Sweden, Norway and Denmark. Vitamin D intake was assessed using a seven-day food record. Serum 25-hydroxyvitamin D (s25OHD) and HbA(1c) were measured, and an OGTT was carried out. Multiple linear and logistic regressions were used for HbA(1c) and cystic fibrosis-related diabetes/OGTT result as outcome variables, respectively. Each model was controlled for country, and for known cystic fibrosis-related diabetes risk factors: age, sex, genotype, liver dysfunction, long-term corticosteroid treatment, and lung and pancreatic function. Results Degree of vitamin D insufficiency (OR 1.36; p=0.032) and s25OHD<30 nmol/l (OR 1.79; p=0.042) were significant risk factors for cystic fibrosis-related diabetes. Accordingly, HbA(1c) value was positively associated with s25OHD<30 nmol/l and<50 nmol/l, as well as with degree of vitamin D insufficiency (adjusted R-2=20.5% and p<0.05 in all). In subgroup analyses, s25OHD<30 nmol/l determined the HbA(1c) value in paediatric patients (adjusted R-2=20.2%; p=0.017), but not in adults. Conclusions/interpretation Vitamin D status is associated with HbA(1c) and diabetes in cystic fibrosis, particularly in children. The study justifies prospective studies on the proposed role of vitamin D deficiency in the pathophysiology of diabetes mellitus