Impact of Vitamin D Levels on Disease Control Across Asthma Subtypes in Mixed-Care Settings

Background: Vitamin D has been implicated in asthma pathophysiology through immunomodulatory and anti-inflammatory mechanisms, although evidence regarding its association with asthma control remains inconsistent. There are no data for the Albanian population that we can use to investigate the level of serum 25(OH)D and its correlation with clinical variables in asthma patients
Methods and Results: This cross-sectional study included 163 adult patients diagnosed with bronchial asthma who were ambulatory, consulted, or hospitalized in the University Hospital Center Tirana, Albania, between November 2024 and October 2025. Asthma control was assessed using the Asthma Control Visual Analogue Scale (AC-VAS; 0-25). Serum 25(OH)D concentration was measured by chemiluminescent immunoassay (CLIA). The primary outcome variable was asthma control measured by the AC-VAS score. Serum 25(OH)D (ng/mL) was analyzed both as a continuous variable and as a categorical variable. Associations were examined using non-parametric tests, linear regression analysis, and moderation analysis (PROCESS macro) to explore potential effect modification by vitamin D status.
Serum 25(OH)D levels were 18.35±8.72 ng/mL, indicating a high prevalence of deficiency. Spearman’s rank correlation analysis demonstrated a statistically significant negative correlation between age and serum 25(OH)D levels (ρ = −0.24, P = 0.003). Serum 25(OH)D levels were positively associated with AC-VAS scores, although this association did not reach statistical significance (P = 0.097). Spearman’s rank correlation analysis demonstrated a statistically significant negative correlation between AC-VAS scores and age (ρ = −0.19, P = 0.015), as well as between AC-VAS scores and body mass index (BMI) (ρ = −0.17, P = 0.031). In the multivariable-adjusted general linear model, age remained independently and negatively associated with AC-VAS scores (B = −0.048, SE = 0.022; P = 0.030). Serum 25(OH)D levels (B = 0.039, SE = 0.036; P = 0.269) and BMI (B = −0.065, SE = 0.057; P = 0.253) were not significantly associated with asthma control after adjustment. Asthma phenotype remained statistically significantly associated with AC-VAS scores in the adjusted model (global test P = 0.031). Among the phenotype categories, phenotype 6 was independently associated with higher AC-VAS scores than phenotype 1 (B = 3.612, SE = 1.198; P = 0.003). The moderation analysis indicated that the association between BMI and asthma control differed according to 25(OH)D category, with a significant conditional effect observed only at serum 25(OH)D levels ≥ 20 ng/mL.
Conclusion: Vitamin D deficiency was highly prevalent among Albanian adults with asthma but was not independently associated with asthma control. Asthma control was associated with age, body mass index, and asthma phenotype. Vitamin D did not show a direct effect but appeared to modify the association between BMI and asthma control, suggesting a context-dependent role. Further longitudinal and interventional studies are required to confirm these findings and clarify their clinical implications.