Associations between Vitamin D Concentrations and Dementia-Related Disorders

This chapter aims to provide an overview and discussion of the current state of evidence regarding vitamin D and de- mentia-related outcomes. A fat-soluble steroid vitamin, vitamin D is essential for healthy bones. In addition to controlling bone health, it is crucial for the operation of other systems like the endocrine, cardiovascular, and nervous systems. Recent data points to its involvement in the decline of amyloid-beta and phosphorylated tau, two markers of Alzheimer's disease. Numerous preclinical investigations have bolstered the theory that vitamin D causes behavioral, attentional, and cognitive deficits. Vitamin D levels are continuously much lower in people with Alzheimer's disease and cognitive impairment than in healthy persons, according to cross-sectional research. Longitudinal studies and meta-analysis have also exhibited an association of low vitamin D with cognitive impairment and Alzheimer’s disease. A prospective study with two follow-ups, each at 5 years, conducted to examine the as- sociation of dietary and supplemental vitamin D intake and cognitive decline showed an association between high intake and a slower decline in the cognitive domains of verbal fluency. Despite such evidence, the causal association cannot be sufficiently answered. In contrast to observational studies, findings from interventional studies have produced mixed results on the role of vitamin D supplementation in the prevention and treatment of cognitive impairment and dementia. The largest problem with the current RCTs is the limited sample size, lack of agreement on the dosage, and age at which vitamin D supplementation to prevent cognitive impairment should be started. Large-scale, double-blind, randomized control trials are therefore required to evaluate the advantages of vitamin D supplementation in the management and prevention of cognitive impairment.