Abstract
Vitamin D is a well-known steroid hormone that plays an important role in controlling bone levels of calcium, phosphorus, and overall mineralization. Several animal and human studies indicate that vitamin D hypovitaminosis may be linked to an increased risk of developing Alzheimer's disease and dementia. The objective of the present review is to summarize current knowledge of the effects of vitamin D deficiency and vitamin D intake on cognitive function. The possible underline mechanisms of these effects were also discussed. We reviewed the literature starting from 1986 to 2019 by searching PubMed, Cochrane, Semantic Scholar, Medline, Scopus, and Cochrane Library databases for all observational studies, randomized clinical trials, meta-analyses, and systematic reviews using the keywords "vitamin D and Alzheimer disease", "neuroprotective effect of vitamin D", "vitamin D deficiency and Alzheimer ", "role of vitamin D in neurodegenerative diseases ", " vitamin D and amyloidogenesis", "acetylcholine and vitamin D", and "memory and vitamin D ".We also referred to animal and in vitro studies that dealt with the possible mechanisms of actions of the neuroprotective effect of vitamin D. Our findings showed that Vitamin D supplementation improves cognitive performance via reducing amyloidogenesis, restoration of neurotransmission, maintaining calcium balance, regulating neurotrophic factors, anti-inflammatory action, apoptosis regulation, antioxidant, and vascular processes. This review might be open new horizons in the understanding of the molecular mechanisms of the disease and neurodegeneration and enable the development of new approaches in treatment and prevention of the disease.