Association between serum 25-hydroxyvitamin D levels and pulmonary function, among Korean adults, during 2010-2014, by sex, age, and body mass index

BACKGROUND

This study examined the association between serum 25-hydroxyvitamin D (25(OH)D) and pulmonary function, among Korean adults, from 2010 to 2014.

METHODS

The data were obtained from the fifth Korea National Health and Nutrition Examination Survey (KNHANES 5), and the first and second year (2013-2014) of KNHANES 6. The study population comprised 14,378 individuals. The variable of interest was serum 25(OH)D, and the dependent variable, pulmonary function.

RESULTS

All people with vitamin D levels below 30 ng/ml had lower lung functions, which was significant in lower forced expiratory volume in the first second (FEV1) (serum 25(OH)D < 10 ng/ml, 20 to <30 ng/ml: P = .001, 10 to <20 ng/ml: P = 0) and forced vital capacity (FVC) (serum 25(OH)D level <10 ng/ml: P = .01, 10 to < 20 ng/ml: P = .001, 20 to <30 ng/ml: P = .008). The lower the serum 25(OH)D, the lower the levels of FEV1 in men and this was significant. (serum 25(OH)D < 10 ng/ml: P = .007, 10 to <20 ng/ml: P = .002, 20 to <30 ng/ml: P = .007). The values of FEV1 and FVC were lower in people aged 50-69 years when vitamin D was lower than 30 ng/ml which were all significant. Among participants with BMI values < 23 kg/m², lower vitamin D levels were significantly associated with lower pulmonary function.

CONCLUSIONS

We found a significant association between serum 25(OH)D and pulmonary function, and this was related to sex, age and body mass index.

Are children with asthma in South Korea also associated with vitamin D deficiency?

Recently, epidemiologic studies have shown that the lack of serum vitamin D levels may be associated with high asthma prevalence, but its effect is still controversial, depending on season, area, and food consumption. We aimed to examine the association of serum vitamin D levels with the prevalence of pediatric asthma in Korea. A total of 80 children (50 asthmatic children and 30 healthy controls) aged 6-14 years were participated in this study. Serum vitamin D levels were measured and compared between the two groups. Moreover, the relationship of serum vitamin D levels with results of pulmonary function test and environmental factors (lifestyle habits and residential factors) collected by a questionnaire survey were examined in asthmatic patients. Serum vitamin D levels in asthmatic children (16.63±4.20 ng/mL) were significantly lower than that in healthy controls (24.24±6.76 ng/mL) (p<0.05). Also, we found that the prevalence of asthma increase to 0.79-fold (odds ratio, 0.79; 95% confidence interval, 0.71 to 0.88; p<0.001) as serum vitamin D level is 1 ng/mL decreases. The increased time spent in outdoor could affect the increases of serum vitamin D levels significantly. However, no associations of serum vitamin D with pulmonary function and residential environmental factors (i.e., housing type, living floor, and indoor activity time) were observed. Our findings suggest that serum vitamin D levels were also associated with pediatric asthma in Korea. Moreover, management of serum vitamin D level in asthmatic children would be a promising approach for preventing exaggeration of their severity.