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

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.

What is already known about this topic? Our study confirm that vitamin D deficit is related to asthma. The strength of our study is that it’s currently the only study that assessed total and free 25(OH)D all together in children with asthma. What does this article add to our knowledge? The total and free serum levels of 25 (OH) D are lower in asthmatic children than healthy ones. Despite expectations, in patients who least control asthmatic symptoms and who have worse respiratory function, total and free vitamin D levels are not significantly lower. How does this study impact current management guidelines? Free vitamin D is rarely investigated in asthmatic children, so further studies are needed to evaluate the relationship about free vitamin D and lung inflammation.

Received: June 2, 2023
Accepted: Sept 7, 2023
Published: Dec 1, 2023

Table of Contents: Vol. 1, n. 4, December 2023

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