Vitamin D and its association with memory and learning: A systematic review and meta-analysis

Vitamin D, which can protect the nervous system, has been associated with increased learning and memory function in studies that have also confirmed a relationship between hypovitaminosis D and cognitive decline. Clinical research, however, has not been promising in this regard and has failed to verify the association between increased vitamin D levels and improved cognitive outcomes. To address this gap, a systematic review and a meta-analysis were conducted to determine the relationship of vitamin D with learning and memory. For this purpose, the ISI, PubMed, and SCOPUS databases were searched for related studies published from 2000 to 2016. The keywords "vitamin D", "1, 25dihydroxycholeclciferol", "learning", "memory", "memory disorders", "Alzheimer's disease", "executive function disorders", "concentration difficulty", "cognitive impairment", "dementia" and "psychiatric test" were used in the search. The data is then analyzed using random-effects meta-analysis model and Stata version 11.2. A total of 11 studies were included in the final analysis. Results showed that although serum levels of vitamin D were positively correlated with memory, learning, and improved cognitive and executive dysfunction, this relationship was not significant (summary OR=1.13, 95% CI: 0.57, 1.68). On the basis of years of study, no correlation was found between the effects of vitamin D and memory and learning. Our findings support the association between serum levels of vitamin D and memory, learning, and improved executive cognitive dysfunction despite the lack of significance in such relationship. These findings emphasize the need for strategies to prevent cognitive and executive dysfunction in patients with severe vitamin D deficiency.