• Eun Jung Byun, Jinyoung Heo, Sang Hyun Cho, Jeong Deuk Lee, and Hei Sung Kim.
• Department of Dermatology, Incheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Incheon, Republic of Korea.
• BMJ Open. 2017 Jul 10; 7 (7): e016409.

ObjectiveTo determine the prevalence and risk factors for suboptimal vitamin D status in Korean adolescents and to assess its relationship with atopic dermatitis (AD) and asthma at a national level.DesignThis is a cross-sectional study with data from the Korean National Health and Nutrition Examination Survey. Information regarding socioeconomic characteristics, clinical data and environmental factors was collected. Blood and urine samples were taken for vitamin D and cotinine, respectively. Descriptive and multivariable logistic regression was performed on the data.SettingSouth Korea (nationwide).Participants2515 individuals aged 10-18 years who participated in the Korean National Health and Nutrition Examination Survey from 2008 to 2011.Main Outcome MeasuresVitamin D status was determined through measurement of serum 25-hydroxyvitamin D (25OHD). Smoking status was classified based on the urine cotinine level. Physician diagnosed with AD and asthma were assessed using a questionnaire.ResultsOverall, 73.3% of the subjects were vitamin D deficient (25OHD <20 ng/mL) and 24.4% of the subjects were vitamin D insufficient (25OHD, 20-29.9 ng/mL). Older age (p<0.001), female gender (p<0.001), urban residence (p=0.019), higher body mass index (p=0.003) and sampling in winter months (November-March) (p<0.001) were independently associated with low serum 25OHD levels. With cotinine verification, 18.2% of the participants were classified as active smokers, and 43.4% were classified as passive smokers. After adjusting for potential confounders, serum 25OHD status showed no association with AD or asthma.ConclusionVitamin D deficiency is highly prevalent in Korean adolescents. Cotinine-verified prevalence of smoking was also high, but its relationship with vitamin D deficiency was not confirmed in our study. Above all, our results provide epidemiological evidence against the association of vitamin D status with AD and asthma at the national level among Korean adolescents.© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

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