Insulin resistance and metabolic syndrome as a risk factor for Alzheimer's Disease: systematic literature review

Abstract

Introduction: It is estimated that worldwide, 65.7 million people will live with the disease in 2030, with Alzheimer's disease being the most prevalent in the world, accounting for 60% of dementia cases. The hypothesis was then raised that through the neuroprotective effect of insulin and insulin resistance in the genesis of Metabolic Syndrome, the hypothetical relationship is made that metabolic syndrome is a risk factor for Alzheimer's disease. Objective: The literature that verifies the impact of vitamin D deficiency on the quality of life of individuals undergoing bariatric surgery was reviewed. Methods: The search strategy was carried out in the virtual databases PubMed, Scielo, LILACS, Scopus, Web of Science, Embase, and Biblioteca Virtual em Saúde, in addition to gray literature such as Google Scholar, OpenGrey, Ibict/BDTD (Brazilian digital library of theses and dissertations) and ProQuest using the Medical Subject Headings (MeSH) and Health Sciences Descriptors (DeCS) descriptors with the Boolean logical operators AND, OR and NOT. The studies considered eligible were those that presented metabolic syndrome as a risk factor for the development of Alzheimer's disease. Results: The online search found 216 studies in virtual bibliographic databases and 70 in gray literature. After removing duplicates, 282 articles remained and were read the title and abstract, with 25 articles chosen for full-text reading, leaving 13 that met the inclusion criteria. Most of the studies included corroborated the hypothesis that metabolic syndrome is a risk factor for Alzheimer's disease. Even the two studies that provide some results in which BMI showed a slower decline in cognitive function, stated that the phenotype studied was that of metabolically healthy obese individuals. Conclusion: The results of this study confirmed the idea that there is an interaction between metabolic health and brain health. First, chronic inflammation and oxidative stress associated with metabolic syndrome can cause damage to blood vessels, compromising cerebral blood flow and impairing the supply of essential nutrients to the brain. Additionally, insulin resistance, one of the key components of metabolic syndrome, can hurt brain function by interfering with the absorption of glucose, a vital fuel for the brain. Finally, how changes in blood lipid levels can contribute to the accumulation of beta-amyloid protein plaques in the brain, one of the markers of Alzheimer's disease.