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Life sciences · Journal article
Theoretical and Natural Science · September 22, 2026
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Vitamin D has been linked to mental health, but the relationship between serum vitamin D and depressive symptoms remains inconsistent. Sleep duration is also strongly related to depression and may provide important context for understanding this association. Focusing on sleep duration as a potential modifying factor, this research explored whether serum 25-hydroxyvitamin D is associated with depressive symptoms among American adults. Publicly accessible NHANES data served as the source for the present analysis.Depressive symptoms were assessed using the PHQ-9, and serum vitamin D was measured as serum 25-hydroxyvitamin D concentration. Sleep duration was included as both a covariate and a possible effect modifier. Exploratory data analysis was first conducted to describe sample characteristics and depressive symptom prevalence across vitamin D groups. Logistic regression models were then fitted to derive odds ratios, both unadjusted and adjusted for covariates. The results showed that vitamin D deficiency appeared to be associated with a higher prevalence of depressive symptoms, but the association was not statistically significant after adjusting for covariates.Sleep duration showed a stronger pattern in the model. Overall, these findings suggest that the vitamin D–depression relationship should not be considered in isolation; sleep duration offers valuable context for future nutritional epidemiology research.