To investigate the value of serum levels of vitamin D and matrix metalloproteinase-9 (MMP-9) in evaluating the severity of asthma in children.

A total of 56 children with acute asthma attacks and 34 healthy children (the control group) in Chengdu Women′s & Children′s Central Hospital from August 2018 to August 2019 were enrolled in this study. And the asthma children were divided into three groups according to the severity degrees: a mild group (n=14), a moderate group (n=25), and a severe group (n=17). The general condition, lung function indexes, serum vitamin D and MMP-9 levels of the four groups were collected and compared, and the correlation between the serum vitamin D and MMP-9 levels and the lung function and severity was analyzed.

The forced expiratory volume in one second (FEV₁), the forced vital capacity (FVC), FEV₁/FVC, the forced expiratory flow at 25% (FEF₂₅), the forced expiratory flow at 50% (FEF₅₀) and the forced expiratory flow at 75% (FEF₇₅) of the asthma children were significantly lower than those of the control group (P<0.05). As the severity of the disease increased, the FEV₁, FVC, FEV₁/FVC, FEF₂₅, FEF₅₀ and FEF₇₅ gradually decreased (P<0.05). The serum vitamin D level in the asthma children was significantly lower than that of the control group and the serum MMP-9 level was significantly higher than that of the control group (P<0.05). As the severity of the disease increased, the level of vitamin D in serum gradually decreased and the level of MMP-9 in serum increased gradually (P<0.05). The FEF₂₅, FEF₅₀ and FEF₇₅ were positively correlated with the serum vitamin D level and negatively correlated with the MMP-9 level (P<0.05). The severity of the disease was negatively correlated with the serum vitamin D level and positively correlated with the MMP-9 level (P<0.05).

In asthma children, the serum vitamin D level is decreased and the MMP-9 level is increased as the severity of the disease increases. Moreover, the two levels are closely related to the lung function, which has high clinical signficance.