The hallmark of cystic fibrosis (CF) is chronic lung inflammation. The severity of lung disease is closely correlated with immunoglobulin G (IgG) levels. Beyond its contribution to the bone health, the importance of vitamin D has not been fully recognized owing to the lack of human studies providing evidence of its benefit. In the context of the recently described immunomodulatory functions of vitamin D, we aimed to assess the relationship between vitamin D and IgG levels.
Eight hundred and ninety-six CF patients were included (0.53-65.9 years) from seven centers in Denmark, Norway and Sweden. Serum 25-hydroxyvitamin D (25OHD) and total IgG were measured, spirometry was carried out and vitamin D intake data were gathered using a 7-day dietary food record. Multiple linear regression analyses were performed for IgG and forced expiratory volume in 1λs (FEV1) as dependent variables, and serum 25OHD, daily food and supplemented vitamin D sources of intake as independent variables. The model was controlled for age, gender, genotype, CF-related diabetes, season, infection/colonization status, long-term oral corticosteroid treatment, long-term treatment with macrolide antibiotics, pancreatic insufficient phenotype and body mass index z-score.
Serum total IgG levels were negatively associated with serum 25OHD (adjusted R (2) = 0.376; beta = -0.02; P<0.001), supplemented vitamin D intake per kg bodyweight (adjusted R (2) = 0.375; beta = -0.82; P < 0.001) and total vitamin D intake per kg bodyweight (adjusted R (2) = 0.398; beta = -0.60; P = 0.002). Serum 25OHD was positively associated with FEV1 (adjusted R (2) = 0.308; beta = 0.0007; P = 0.025).
Increasing vitamin D intake may positively modulate inflammation in CF. This study supports the proposed role of vitamin D in the immune system during infection and substantiates prospective studies.