Vitamin D deficiency is associated with decreased lung function in Chinese adults with asthma

Background: Vitamin D deficiency has been associated with markers for allergy and asthma severity in children with asthma. However, its association with Chinese adult asthmatics has not been studied. Objective: To examine whether vitamin D status is associated with lung function and total serum IgE in Chinese adults with newly diagnosed asthma. Methods: We conducted a cross-sectional study including 435 Chinese patients aged >18 years with newly diagnosed asthma. Vitamin D status was assessed by measuring serum 25 hydroxyvitamin D (25OHD) concentrations. The primary outcomes included airflow limitation, as measured by the forced expiratory volume in 1 s (FEV ₁), FEV₁ % predicted, and FEV₁/forced vital capacity (FVC), and serum total IgE concentration. Results: Vitamin D deficiency was prevalent in Chinese adults with asthma, with 88.9% of the subjects having 25OHD <50 nmol/l. Serum 25OHD concentration was positively correlated with FEV₁ % predicted (p = 0.02, r = 0.12). After adjusting for age, sex, body mass index, smoking, month of blood collection, and symptom duration, we found significant positive associations between 25OHD concentrations and FEV₁ (in liters), FEV₁ % predicted, and FEV ₁/FVC (p for trend < 0.05 for all). The adjusted odds ratios for the highest versus the lowest 25OHD quartile were 0.50 (0.26-0.96) for FEV ₁ <75% predicted and 0.44 (0.20-0.95) for FEV₁/FVC% <0.75. There was no significant association between 25OHD concentrations and total IgE. Conclusions: Vitamin D deficiency was highly prevalent in Chinese asthma patients, and vitamin D status was associated with lung function.