Childhood asthma and vitamin D deficiency in Turkey: is there cause and effect relationship between them?

BACKGROUND: Epidemiological studies show that vitamin D deficiency and insufficiency are common worldwide and associated with many diseases including asthma. Our aim was to evaluate vitamin D insufficiency and its clinical consequences. METHODS: This cross-sectional study was carried out on 170 children consisted of 85 who were asthmatic and 85 who were not, aged 2 to 14 years in Tekirdag, Turkey, from September 2009 to May 2010. Children’s basal serum D vitamin levels were determined, and their eating habits, vitamin D intake, exposure to sunlight and use of health services during the previous year were investigated. The severity of asthma and levels of asthma control were assessed according to the Global Initiative for Asthma guidelines. RESULTS: The difference between mean vitamin D levels in the asthmatic group (mean +/- SD) 16.6 +/- 8.5 ng/mL and the healthy control group (mean +/- SD) 28.2 +/- 19.5 ng/mL was found to be statistically significant (p < 0.001). Children in the asthma group had less exposure to sunlight and ate a diet less rich in vitamin D (p < 0.001). A significant difference was observed between the groups regarding the frequency of respiratory tract infections leading to emergency unit admissions and number of hospitalizations (p < 0.001). It was also shown that a decrease in vitamin D level increased the severity of asthma (p < 0.001) and decreased the frequency of controlled asthma (p = 0.010). CONCLUSION: This study has demonstrated the correlation between plasma 25 (OH) D levels and childhood asthma. Evidently, this relationship being influenced by multiple factors other than vitamin D, further studies should be conducted to explore the interrelation between all such factors.