Vitamin D and asthma in children: insights from total and free 25-hydroxyvitamin D and vitamin D binding protein measurements

ABSTRACT
The relationship between serum concentrations of total vitamin D [25(OH)D] and free vitamin D [free 25(OH)D] remains unclear in childhood asthma.
The primary objective was to assess serum levels of 25(OH)D, free 25(OH)D, and vitamin D binding protein (VDBP) in children with asthma compared to healthy children. The secondary objective was to explore potential associations with asthma control and lung function.
50 atopic children, 6-16 years old, with diagnosis of mild-moderate persistent asthma and 40 healthy children of the same age were recruited. In the asthmatic group, the Asthma Control Test (ACT) questionnaire was administered, and lung function was assessed using spirometry. Total 25(OH)D, free 25(OH)D, and VDBP were measured in all participants.
Total 25(OH)D levels were significantly lower in asthmatic children compared to non-asthmatics (mean values: 24.6 ± 8.2 ng/ml vs. 29.6 ± 11.7 ng/ml, p < 0.03). Free 25(OH)D levels in asthmatic subjects were lower than in non-asthmatic subjects (mean values: 3.2 ± 2 ng/ml vs. 6.4 ± 4.5 ng/ml, p < 0.0001). The VDBP values were comparable between the two groups (mean values: 239.28 ± 25 μg/ml vs. 250 ± 30 μg/ml, p > 0.05). There was no significant correlation observed between ACT score, FEV1, and serum levels of vitamin D or VDBP.
Our data show that the total and free serum levels of 25 (OH) D are lower in 32 asthmatic children than healthy ones. We found no correlation between asthma control, lung function and free and total vitamin D levels.