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.