Plasma 25-hydroxyvitamin D levels, quality of life, inflammation and depression in older adults: Are they related?

Background and objectives: This study aimed to determine whether there is an association between inflammation and depression taking into account the effect of several confounders, but specially plasma 25-hydroxyvitamin D (25{[}OH]D) levels. Material and methods: A cross-sectional study was conducted on adults (n = 346) aged 60 years or older recruited from primary healthcare centres. Depression was assessed by the Geriatric Depression Scale (GDS), while plasma 25(OH)D and inflammatory cytokines were measured following routine biochemical laboratory protocols. Results: Subjects were divided into two subgroups according to their depression status, and matched in their baseline conditions using random forest-based propensity scores. Both groups were rather similar in regard to most variables, apart from quality of life (p < 0.001) and plasma levels of IL-6 (p = 0.03). The overall prevalence of vitamin D deficiency was 36.3% (95% Confidence Interval {[}95% CI], 30.2%-42.5%), without a significant difference between depression groups (p = 0.2). A significant association was observed between GDS score and plasma IL-6 levels only among those with SF-6D score between 0.26 and 0.50 (p = 0.001). Conclusions: The association between inflammation and depression is more likely to be due to a moderation influence of quality of life rather than plasma 25(OH)D levels. However, further studies are needed to ascertain the effect of a poor quality of life leading to chronic inflammation and poor health upon longer periods of followup. (AU)