Associations Between Intrathecal Levels of Vitamin D, Cytokines, and Core Biomarkers of Alzheimer's Disease: A Cross-Sectional Study

Background: Several studies have examined association between vitamin D levels in serum and cognition, but little is known of vitamin D levels in cerebrospinal fluid (CSF) and association with Alzheimer's disease (AD). Objective: In this cross-sectional, explorative studyweinvestigated possible associations of vitaminDinCSFwith biomarkers for AD, amyloid-beta, tau protein/phosphorylated tau protein in CSF, and with the cytokines IL-6, IL-8, and TNF-alpha in CSF in patients with cognitive impairment and cognitively healthy controls. Methods: We included 100 outpatients >= 65 years referred for assessment of cognitive impairment and 76 age- and sexmatched cognitively healthy controls. Levels of 25-hydroxyvitaminD(25(OH)D), amyloid-beta, tau protein and phosphorylated tau protein, as well as IL-6, IL-8, and TNF-alpha, were analyzed in CSF in both groups. Results: Higher levels of 25(OH)D in CSF in all groups together were associated with lower levels of tau protein (p = 0.01) and phosphorylated tau protein (p = 0.005). We found no association between 25(OH)D levels in CSF and pathological levels of amyloid-beta in CSF nor levels of IL-6 or TNF-alpha in CSF. Higher levels of 25(OH)D in CSF were associated with higher levels of IL-8 in CSF (p = 0.002). However, vitamin D explained only 6% of variance in IL-8. There was no significant difference between the patient groups and the control group regarding the association between 25(OH)D in CSF and any of the three cytokines in CSF. Conclusion: Participants with higher CSF levels of 25(OH)D exhibited reduced CSF levels of tau protein and phosphorylated tau protein.