Vitamin deficiencies and Alzheimer’s disease. Evidence and implications for supplementation

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by beta-amyloid (Aβ) deposition, hyperphosphorylation of tau protein (pTau), mitochondrial impairment and neuroinflammation. Several risk factors, such as aging, genetics, cardiovascular diseases (CVD) and lifestyle, concur to the onset of the disease. Among modifiable risk factors, micronutrient intake has gained attention for its potential role in preventing or slowing down disease progression. In this narrative review, we summarize current evidence linking vitamin deficiencies to the onset and progression of AD. We analyze evidence for fat-soluble (A, D, E, K) and water-soluble vitamins (C and B-complex, both canonical B1–B12 and non-canonical forms such as B13, B15, and B17). We then analyze individual and combinational vitamin supplementation in AD patients as the primary focus, with additional data derived from animal and cellular studies when human data are limited. As final result, B6, B9, and B12 vitamins have demonstrated promising effects in clinical trials. Interestingly, some beneficial effects have also been observed in the prodromal stage of AD when these vitamins were combined with antioxidant compounds such as vitamin C and vitamin E. Given the multifactorial nature of AD, targeting isolated vitamin deficiencies may not be sufficient. Future research should focus on long-term clinical trials (at least 2 years), particularly exploring combinations of vitamins and antioxidants, to achieve meaningful therapeutic effects. This review is intended as a point of support for future clinical trials in the treatment of AD from a nutritional point of view.