THE PARADOXICAL ROLE OF VITAMIN D IN ALZHEIMER’S DISEASE: A CRITICAL REVIEW OF CURRENT EVIDENCES

Abstract

The increasing prevalence of Alzheimer's Disease (AD) has driven the search for modifiable risk factors, with vitamin D status emerging as a focal point of intense scientific interest. This micronutrient has receptors (VDR) widely distributed in brain areas crucial for cognition and memory, such as the hippocampus and the cortex. The objective of this study is to critically analyze the available scientific evidence regarding the relationship between vitamin D and Alzheimer's Disease, exploring its potential neuroprotective effects and the paradoxical findings associated with supplementation. This study is a critical narrative review of the literature, conducted between November 2025 and January 2026, based on scientific evidence demonstrating that this nutrient has a controversial relationship—both in reducing and potentially exacerbating the progression of Alzheimer's Disease. Some findings have shown that Vitamin D possesses strong anti-inflammatory and antioxidant properties supported by plausible biological mechanisms, acting as a neurosteroid hormone that regulates the expression of genes associated with amyloid pathology. However, other research suggests a potential worsening of brain pathology and an increase in mortality among patients already diagnosed. Consequently, these discrepancies in results clarify that the relationship between vitamin D and AD is complex, multifaceted, and not fully elucidated; they may be attributed to methodological differences, study populations, and the vitamin D formulations used. While maintaining serum levels of this nutrient is crucial for prevention, large-scale, long-term supplementation requires rigorous supervision, especially in patients already diagnosed with the disease.