Is Vitamin D Deficiency Linked to Depression? Insights from a Nationally Representative US Sample

BackgroundVitamin D deficiency (VDD) has been known to be involved in neuropsychiatric conditions, including depression. However, the association between VDD and specific depressive symptoms remains unclear. This study aims to investigate the relationship between VDD and individual depressive symptoms using data from a large, nationally representative U.S. population. MethodsWe conducted a retrospective cross-sectional analysis of 10,914 adults from the 2007 to 2018 NHANES cycles with available serum 25(OH)D levels and complete PHQ-9 derived Depression Screener (DPQ) data. VDD was defined as <30 ng/mL. Specific depressive symptoms like little interest, feeling depressed, low energy, negative self-image, and suicidal ideation were assessed. Multivariable logistic regression was performed after adjusting for demographics and comorbidities. ResultsVDD was present in 8% of participants and was more prevalent among younger adults, females, and individuals with obesity. Key depressive symptoms such as low interest (29.9% vs. 24.8%), feeling down (30.4% vs. 24.5%), and fatigue (55.0% vs. 48.9%) were significantly more common in the VDD group (p < 0.01 for all). VDD was independently associated with increased odds of any depressive symptoms (adjusted odds ratio [aOR] 1.18; 95% CI: 1.02-1.36; p = 0.028). Female gender (aOR 1.78; 95% CI: 1.65-1.92; p <0.001), age <60 (aOR 1.49; 95% CI: 1.36-1.63; p <0.001), obesity (aOR 1.21; 95% CI: 1.11-1.32; p <0.001), diabetes (aOR 1.32; 95% CI: 1.16-1.49; p <0.001), hypertension (aOR 1.25; 95% CI: 1.14-1.37; p < 0.001), and high triglycerides (aOR 1.19; 95% CI: 1.08-1.30; p = 0.0003) were stronger predictors of depression. ConclusionVDD is modestly but significantly associated with depressive symptoms, particularly little interest and low energy. Although the effect size is smaller than that of metabolic and demographic factors, VDD may represent a modifiable target in depression prevention and management strategies.