Cognitive decrease in Turkey's elderly population relationship with vitamin D deficiency: A systematic examination

Objective: This research aims to obtain evidence-based scientifically proven data and contribute to the literature as a result of systematic review of studies on the relationship between vitamin D deficiency and cognitive impairment such as dementia, Alzheimer's (AD) and Parkinson's (PD) in the older population in Turkey. Method: Published studies covering the relationship between vitamin D deficiency and cognitive status, dementia, AD and PD in the older adults in Turkey, were scanned and examined under the systematic review approach. Secondary data were accomplished from the data base of Google Academic, Pubmed Health, DergiPark, National Thesis Center of the Council of Higher Education. The studies published between 1965-2021 and 1970-2021, were searched and selected according to criteria previously agreed with PRISMA and accepted for evaluation. Results: A total of 10 studies, including 6 research articles and 4 graduate theses, were accepted for the evaluation. These studies were evaluated in detail in terms of method, number of subjects, vitamin D threshold values and cognitive measurement tests. Vitamin D levels of individuals with dementia, Alzheimer's and Parkinson's disease were found to be low. Vitamin D deficiency is of vital importance, especially for individuals living in care centers. Conclusion and Discussion: Diseases such as dementia, AD and PD are increasing among older individuals in Turkey and in the world. Research shows the importance of the relationship between cognitive decline and vitamin D deficiency. Differences such as the methods and threshold values and the number of subjects in the studies reduce the statistical level of reliability of the comparison. Vitamin D can be used as a biomarker in disease diagnosis. Although some research results show the relationship between vitamin D level and cognitive function, detailed research is required for strong evidence.