Introduction: Low vitamin D status is a widespread problem in the US [1, 2]. Research has shown that serum vitamin D concentrations previously considered in the normal range are not sufficient for optimal health [3]. Vitamin D plays a role in a wide range of ailments such as osteoporosis, cancer, cardiovascular diseases, and diabetes [4, 5]. Recently, a role for vitamin D in cognitive function and mental health has been reported [6, 7]. Vitamin D concentrations have been shown to be low in patients suffering from mood disorders and have been associated with cognitive function [8, 9]. Depression is one of the leading causes of disability in the US among young adults. In the US, in a given year, about 26% of population, aged ≥18 years suffer from a diagnosable mental disorder and about 6% (1 in 17) suffer from a serious mental disorder [10]. Several mechanisms of action have been proposed to explain the association between vitamin D and depression. The role of calcitriol or 1, 25 dihydroxy cholecalciferol, the bioactive form of vitamin D, in brain tissue has been confirmed by the presence of vitamin D receptors (VDR) and hydroxylases in various brain regions [11, 12]. One area where VDR and hydroxylases have been found is the amygdala, which is the center of the limbic system, where behavior and emotions are regulated [13]. Vitamin D has been reported to exert a neuroprotective function through several mechanisms. Calcitriol regulates calcium concentrations intra- and extracellularly in neurons, consequently reducing toxicity caused by excess calcium [14–16]. A few studies have found an association between serum vitamin D concentrations and depression [17–20]. Light therapy has been shown to improve the depression in adjunction with antidepressants, which may be in part due to improved vitamin D synthesis associated with light therapy [21]. Majority of the studies relating vitamin D status with depression are based either on a small sample size or non-representative of the US population. Very little is reported on the association between vitamin D concentrations and depression in young adult US population. Overall, the previous studies on the association between vitamin D status and depression yielded equivocal results [22–25]. Therefore, the aim of this study was to investigate the association between serum vitamin D concentrations (25 hydroxy cholecalciferol ) and depression in a large, nationally representative sample survey of the US population, the Third National Health and Nutrition Examination Survey (NHANES III).
Methods: Data from the third National Health and Nutrition Examination Survey were used to assess association between serum vitamin D and depression in 7970 non-institutionalized US residents, aged 15-39 y. Assessment of depression was done using the Diagnostic Interview Schedule developed by the National Institute of Mental Health. After accounting for several confounding variables in multivariate logistic regression analysis, we estimated odds ratios (OR) for having depression in vitamin D deficient persons in comparison to vitamin D sufficient persons
Results: Women, non-Hispanic blacks, persons living below poverty, persons who did not consume supplements, persons living in South and West regions and in urban areas, persons with higher BMI, and persons with current depression had higher prevalence of vitamin D deficiency compared to their counterparts. OR for having current depressive episodes in persons with serum vitamin D ≤ 50 nmol/L is significantly higher relative to those with serum vitamin D ≥ 75 nmol/L (OR = 1.85; P = 0.021).
Conclusion: In this large population based study, likelihood of having depression in persons with vitamin D deficiency is significantly higher compared to those with vitamin D sufficiency. Early diagnosis and intervention are paramount because coexistence of vitamin D deficiency and depression has serious negative consequences on health.