The Efficacy of Vitamin D Supplementation in Patients With Alzheimer's Disease in Preventing Cognitive Decline: A Systematic Review

Abstract

To evaluate the role of vitamin D supplementation in preventing cognitive decline in patients with Alzheimer's disease (AD), five databases such as PubMed, PubMed Central (PMC), Medical Literature Analysis and Retrieval System Online (MEDLINE), ScienceDirect, and Google Scholar were searched for articles relevant to the research question with filters such as English and human studies from 2011 to 2022. Two investigators extracted the data and assessed the quality of the study using the predefined criteria. We identified 24 relevant articles after the critical screening. There were five randomized controlled trials (RCTs), two observational studies, two systematic reviews and meta-analyses, one pilot study, and 14 review articles.Most RCTs showed no significant improvement in vitamin D supplementation except for one study, which reported significant improvement in cognition on taking vitamin D in Alzheimer's disease but was not taken much into consideration as it had a small sample size (n=210) and was for a shorter duration. Another study evidenced significant improvement in Mini-Mental State Examination (MMSE) score when memantine and vitamin D were taken together compared to when memantine and vitamin D were taken independently. Studies have shown that vitamin D deficiency is associated with an increased risk of developing cognitive impairment. But there is no sufficient evidence indicating vitamin D supplementation can improve cognitive function in Alzheimer's disease.

Vitamin D Reduces GABA-Positive Astrocytes in the 5xFAD Mouse Model of Alzheimer’s Disease

“…These findings propose that insufficient vitamin D levels may contribute to the progression of AD, with possible implications for prevention and treatment strategies [26]. However, the effects of vitamin D on the pathological process of AD were controversial [6,[27][28][29]. We employed an AD mouse model to examine the impact of vitamin D on AD and determine whether vitamin D supplementation may help mitigate the pathological process of AD.…”

The Impact of Vitamin D on Alzheimer's Disease: A Mendelian Randomization Study

“…The role of vitamin D supplementation in preventing or treating AD remains contentious 23 . While some population studies suggest that vitamin D supplementation could be bene cial in preventing or delaying the onset of AD [24][25][26][27] , other studies indicate that vitamin D supplementation may be ineffective or even harmful, particularly in the early stages of AD 12,13 . This phenomenon could involve the complex role of vitamin D at different stages of AD pathology and how the dosage and timing of supplements might differentially impact disease progression.…”

“…De ciencies in vitamin D levels have been associated with a variety of health issues 10,11 , including an increased risk of developing AD. However, the causal relationship between vitamin D levels and AD remains a topic of debate 12,13 .…”

Asociación entre bajos niveles de vitamina D y deterioro cognitivo en personas mayores chilenas: Resultados de la Encuesta Nacional de Salud 2016-2017

“…La vitamina D tiene un papel relevante en el metabolismo del calcio, junto a propiedades antiinflamatorias y antioxidantes; pero además se le ha asociado recientemente propiedades neuroprotectoras al promover la eliminación de placas amiloides por parte de los macrófagos, reduciendo así la neurodegeneración 21 . Consecuentemente, se ha establecido, que su suplementación mejoraría la capacidad cognitiva de las personas mayores y mantendría la salud neuronal 22 ; de ahí la importancia de estudiar el impacto de la deficiencia de vitamina D en la cognición.…”