Bedolla-Barajas and colleagues examined vitamin D insufficiency and deficiency in 135 Mexican patients with allergic asthma.¹ Vitamin D insufficiency was common in the group: 25.2 % as well as deficiency: 71.1 %. Noteworthy, there was no difference between genders.

There is a growing body of evidence that vitamin D exert a relevant immunomodulatory effect on immune cells, that may be able to explain the close link between vitamin D and respiratory disorders.^2,3

On the other hand, the control of asthma is the cornerstone strategy in the management of patients with asthma as stated by the Global Initiative for Asthma (GINA) document.⁴ The asthma control evaluation is based on a global assessment of respiratory symptoms, lung function, bronchial inflammation, comorbidity (including obesity, upper airways disorders, gastroesophageal reflux, emotional problems, nocturnal apnea), risk factors, compliance, and adherence to treatments. Unfortunately, the study of Hall and colleagues, even though conducted on a very large population, did not addressed this issue. So, the aim of this study was to identify the impact of vitamin D serum levels on some clinical and functional characteristics in a group of 126 outpatients (85 females, mean age 56.93 ± 13.66 years) with asthma.

The informative factors and the vitamin D were selected for multivariate analysis, that it was performed using the multinomial logit regression and the model selection was done by the Akaike an Information Criterion. Differences, with a p-value less than 0.05, were selected as significant and data were acquired and analyzed in R v3.3.3 software environment.⁵

Table 1A reports clinical and functional data of outpatients. Regarding vitamin D categorization, 16 subjects (12.7 %) had sufficient serum level, 54 (42.86 %) had insufficient serum level, and 56 (44.44 %) had deficient serum level. More in detail, subjects with sufficient vitamin D serum level showed a mean of 38.34 ng/mL (SD = 9.79) ng/mL, while patients classified in insufficient and deficient vitamin D group had a mean value of 24.43 ng/mL (SD = 2.64) and 13.01 ng/mL (SD = 4.29), respectively.

At multivariate analysis, a significant effect of the GINA asthma control grade and the FVC on vitamin D was observed (p-values < 0.05). In particular, the FVC were positively associated with insufficient vitamin D values (OR = 1.04; p-value = 0.04), while having insufficient vitamin D among patients with partially controlled asthma was been about 73 % less likely than that in patients with controlled asthma level (OR = 0.27; p-value = 0.03), as reported in Table 1B.

The present experience, although performed on a limited group of outpatients, underlines the impact of vitamin D insufficiency/deficiency on the asthma control grade and is consistent with studies supporting a pathogenic role of vitamin D in asthma.