Epidemiological studies have established a relationship between low levels of serum vitamin D and reduced lung function in healthy adults and asthma onset and severity in children. However, no study has examined the relationship between vitamin D levels and exercise-induced bronchoconstriction in asthmatic children.

We evaluated the relationship between 25-hydroxyvitamin D concentrations and baseline forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and the percentage fall in FEV1 (ΔFEV1) after a standardized exercise challenge in 45 children with intermittent asthma. Only 11% of the children had desirable serum vitamin D levels (at least 30 to 40 ng·mL(-1)).

A positive correlation was found between serum 25-hydroxyvitamin D and both FVC (r=0.34, p=0.037) and FEV1 (r=0.32, p=0.037). Subjects with a positive response to the exercise challenge (ΔFEV1≥10%) presented lower serum levels of 25-hydroxyvitamin D than children with a negative challenge- 16.2 (5.2) vs 23.4 (7.0) ng·mL(-1) (p=0.001), respectively.

Our results indicate that hypovitaminosis D is frequent in asthmatic children who live in a Mediterranean country. In those children, lower levels of vitamin D are associated with reduced lung function and with increased reactivity to exercise.