Associations between vitamin D and depression in institutionalized oldest old

Aim. To examine the relationship between vitamin D levels and the prevalence and severity of depression in people aged ≥90 living in the nursing homes. Materials and methods. A cross-sectional study was conducted on 351 people (25% men) aged 90-104, with a median age of 92, who were permanently residing in Moscow nursing homes. The Geriatric Depression Scale (GDS-15) was used to detect depression, with possible depression diagnosed at a score of 5. Vitamin D (25-hydroxycalciferol) levels were determined in blood serum using chemiluminescence analysis on microparticles, with normal levels ranging from 30 to 100 ng/ml. Results. Depression is diagnosed in 67,2% of the oldest old. Vitamin D levels range from 3 to 36 ng/ml (median 6, interquartile range 5-8), and less than 1% of those with the highest vitamin D levels have a vitamin D deficiency. The absolute median difference in vitamin D between the oldest with and without depression is 2 ng/ml (p<0.001). A single-factor regression analysis shows that vitamin D in the institutionalized oldest old has a protective effect on depression: increasing vitamin D levels per 1 ng/ml reduces the chance of depression by 14% (OR 0,86; 95% CI 0,81-0,92; p<0,001). After adjusting for age, sex, children, education, and physical activity in the regression model, the association between vitamin D and depression remains significant for both vitamin D and high levels of physical activity as predictors of depression with protective effect: vitamin D (OR 0,86; 95% CI 0,80-0,93; p<0,001); high level of physical activity (OR 0,47; 95% CI 0,27-0,81; p=0,007). ROC analysis confirms a correlation between vitamin D and depression. Vitamin D levels ≤12 ng/ml predict depression levels with 71% sensitivity, 70% specificity, and 71% diagnostic accuracy. The ROC-curve area below 0.666 indicates a satisfactory model quality. The single-factor regression analysis shows that the chances of depression are 5,6 times higher at vitamin D levels of ≤12 ng/ml (OR 5,60; 95% CI 2,47-12,70; p<0,001). Conclusion. Associations between vitamin D and the presence and severity of depression among the oldest old living in the nursing homes in Moscow have been identified.