A high prevalence of vitamin D deficiency has been reported among adolescent girls and young women in Korea. Women of this age have a higher risk of vitamin D deficiency than those in other age groups, but few studies have examined for independent determinants of this deficiency in this population. Recently, some studies have reported an association between vitamin D deficiency and the risk of obesity and anemia among adolescent girls and young women in Korea. However, these studies did not consider potential confounding factors or participants with prevalent chronic disease, which may lead to the biased results. Therefore, the present study aimed to (1) identify the independent determinants of serum vitamin D levels; (2) evaluate the association between vitamin D deficiency and risk of obesity; and (3) investigate whether vitamin D deficiency is associated with anemia among adolescent girls and young women in Korea.
We analyzed data for adolescent girls aged 12-18 years and young women aged 19-29 years who participated in the Korea National Health and Nutrition Examination Survey (KNHANES) in 2008-2014. Demographic and lifestyle factors were assessed by a self-administered questionnaire from the health interview survey. Serum vitamin D, hemoglobin, ferritin, and other blood biomarkers were obtained from the health examination. Vitamin D deficiency was defined as a serum 25-hydroxyvitamin D (25(OH)D) levels of less than 20 ng/mL. Multivariate generalized linear regression and unconditional logistic regression were used, taking into consideration the complex design of the KNHANES.
Results 1: The analysis included 1,574 adolescent girls and 2,022 young women. We found that physical activity and alcohol consumption levels were significant independent determinants among adolescent girls. Among young women, independent determinants included physical activity levels, current smoking, and use of dietary supplements and oral contraceptive.
Results 2: A total of 3,617 adolescent girls and young women were included in this analysis. After adjustment for multiple confounding variables, the vitamin D deficient group had 1.58 (body mass index≥25 kg/m2, 95% confidence interval (CI): 1.01-2.48) times higher prevalence of obesity, and 1.61 (body fat percentage≥30%, 95% CI: 1.08-2.40) times higher prevalence of excess body fat percentage, compared to the vitamin D sufficient group. However, no significant association was observed between vitamin D deficiency and abdominal obesity (waist circumference≥85cm, odds ratio (OR): 0.97, 95% CI: 0.54-1.73).
Results 3: For the association between vitamin D deficiency and the prevalence of anemia, we included 3,560 adolescent girls and young women in the analysis. We found that vitamin D deficiency was associated with a higher prevalence of anemia (OR: 2.07, 95% CI: 1.15-3.70) and iron deficiency anemia (OR: 1.49, 95% CI: 1.02-2.19) than vitamin D sufficiency in multivariable adjusted models.
The results of this study identified several independent factors that were correlated with serum 25(OH)D levels among adolescent girls and young women in Korea. Our findings suggest that it is necessary to monitor and manage these factors in order to reach an optimal serum vitamin D levels. In addition, individuals with vitamin D deficiency tended to have higher prevalence of obesity and anemia. Future large prospective cohort studies and randomized clinical trials are needed to confirm this association.