Document Type


Degree Name



Dept. of Public Health & Preventive Medicine


Oregon Health & Science University


Depression is a serious mental illness, with an estimated prevalence of 6.7% of American adults according to the 2001-2003 National Comorbidity Survey Replication35. Recent studies indicate that there may be a link between insufficient vitamin D and depression. Because the primary source of vitamin D is synthesis in the skin via exposure to ultraviolet light, sun protection behaviors such as sunscreen and avoiding sun exposure may limit vitamin D synthesis. This study uses 3,367 individuals who participated in the National Health and Nutrition Examination Survey (NHANES) to explore whether compliance with recommended sun protection behaviors is associated with lower serum vitamin D, and whether lower vitamin D is associated with depression. Frequent sun exposure protective behavior, as operationalized in this study, was found to be associated with lower vitamin D (β=-0.672, p=0.044), and suboptimal vitamin D was found to be associated with clinical depression (β=0.500, p=0.003). However, there was no direct association between sun exposure protective behavior and clinical depression (β=-0.076, p=0.620). Although not significant ( , p=0.180), the magnitude of the odds ratios suggests there may be an interaction. In those with optimal vitamin D, increased frequency of sun exposure protective behavior is non-significantly associated with lower risk of depression (Moderate vs. Rare OR= 0.54, 95% CI 0.27, 1.07. Frequent vs. Rare: OR=0.32, 95% CI: 0.05, 2.34), while in those with deficient vitamin D, more frequent sun exposure behavior is associated with non-significantly higher risk of depression (Moderate vs. Rare OR= 1.23, 95% CI 0.93, 1.62. Frequent vs. Rare: OR=1.52, 95% CI: v 0.49, 4.66). Serum vitamin D level was no longer significantly correlated with depression after covariates were included in the model (BMI, gender, vitamin D supplementation, race/ethnicity, arthritis, smoking status and physical activity level). Overall, sun exposure protection behaviors may prevent individuals from maintaining healthy levels of vitamin D. There may or may not be a causal relationship between lower vitamin D and higher risk of depression. Attempting to evaluate the association between the two is made complicated by uncertainty about the accuracy of the current clinical cutoffs as predictors of poor health outcomes associated with insufficient vitamin D. There is not sufficient evidence to conclude an association between sun exposure behavior and depression—more detailed information about sun exposure and protective behaviors is needed.




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