Correlation between vitamin D serum levels and passive smoking exposure in children with asthma.

Objective: To establish the relationship between vitamin D serum levels, pulmonary function, asthma control, and passive smoking exposure in children with asthma.
Methods: We studied the relationship between 25-hydroxy cholecalciferol (25[OH]D) concentrations and baseline spirometry and levels of asthma control, and the effect of parental tobacco smoke exposure in 152 white children (84 boys [55.3%]) with a mean age ± standard deviation of 9.9 ± 2.0 years (range 5-15 years) in a cross-sectional study carried out during the winter and early spring.
Results: Only 9.9% of our children had a sufficient serum 25(OH)D level (at least 30-40 ng/mL). A significant positive correlation was found between the force vital capacity % predicted, forced expiratory volume in the first second of expiration % predicted, and serum 25(OH)D level (r = 0.36, p < 0.001 for both). The subjects with controlled asthma had higher serum levels of 25(OH)D than children with partially controlled or noncontrolled asthma, both according to Global Initiative for Asthma parameters and the Test for the control of asthma in childhood (p = 0.011). Children with both nonsmoking parents presented significantly higher serum levels of 25(OH)D than children with both smoking parents (median, 20.5 ng/mL [interquartile range {IQR}, 16.6-24.0 ng/mL] versus median, 14.5 ng/mL [IQR, 11.1-19.1 ng/mL], respectively; p < 0.001), with intermediate values for children exposed to single maternal (median, 20.3 ng/mL [IQR, 13.0-23.2 ng/mL]) or to paternal smoking (median, 17.8 ng/mL [IQR, 14.7-22.1 ng/mL]).
Conclusion: Our results indicated that hypovitaminosis D was frequent in children with asthma who lived in a Mediterranean country. In these children, lower levels of vitamin D were associated with reduced asthma control and passive smoking exposure.