The association of vitamin D deficiency, age and depression in US adults: a cross-sectional analysis

Background Depression is an important public health burden, its risk of occurrence is associated with vitamin D deficiency and may also increase with age, while serum vitamin D levels are closely related to age. Objective The purpose of this study was to evaluate whether vitamin D and age are associated with depression after adjustment for each other. Materials and methods We extracted data from NHANES 2013–2018, including demographic characteristics, depression level, vitamin D level, physical activity, and body measures. A total of 15,156 adults aged 20 years or older (mean age 49.81 ± 17.67 years, 7301 males and 7855 females) were included. Depression was screened by PHQ-9. Vitamin D deficiency was defined by a serum vitamin D level < 30nmol/L. We performed binary logistic regression models to analyze the association between vitamin D, age and depression, respectively. Results Vitamin D levels were negatively associated with depression ( P < 0.001). Vitamin D had a significant effect on depression (OR = 0.776, 95%CI: 0.682–0.884, P < 0.001), the effect remained significant after adjusted for confounding variables (OR = 0.761, 95%CI: 0.663–0.874, P < 0.001). Age was positively associated with depression ( P < 0.001) and had a significant effect on depression (OR = 1.079, 98%CI: 1.032–1.128, P = 0.001), the effect remained significant after adjusted for confounding variables (OR = 1.092, 95%CI: 1.040–1.146, P < 0.001). Age and vitamin D levels were positively correlated ( P < 0.001), and older age had a significant effect on vitamin D level (OR = 1.526, 95%CI: 1.416–1.645, P < 0.001), the effect remained significant after adjusted for confounding variables (OR = 1.371, 95%CI: 1.263–1.487, P < 0.001). In addition, the prevalence of depression was higher in females (2312/7855, 29.43%) than in males (1571/7301, 21.52%), and the difference was statistically significant ( P < 0.001). Conclusions Vitamin D deficiency and older age are both associated with higher risk of depression, while older age is a protective factor for vitamin D deficiency.