Spermidine in Alzheimer’s Disease: Evidence from Animal Models and Human Studies

Abstract: Spermidine is a naturally occurring polyamine involved in multiple cellular processes, including growth regulation, protein translation, and autophagy. Increasing attention has been devoted to its potential neuroprotective effects, particularly in Alzheimer’s disease (AD), a neurodegenerative disorder characterized by β-amyloid and phosphorylated tau accumulation, synaptic dysfunction, and progressive neuronal loss. In this narrative review, we examine potential mechanisms through which spermidine may influence AD pathophysiology and summarize available preclinical and clinical evidence. Preclinical studies indicate that spermidine induces autophagy, a key cellular clearance pathway responsible for removing damaged organelles and aggregated proteins. Because impaired neuronal autophagy contributes to the accumulation of β-amyloid and tau in AD, increasing intracellular spermidine levels may enhance the degradation of these toxic species. In addition, spermidine exhibits anti-inflammatory and antioxidant properties, attenuates microglial activation, and supports mitochondrial function. In animal models of AD and brain aging, spermidine administration has been associated with improvements in cognitive performance and synaptic function. However, human clinical evidence remains limited and largely inconclusive. Observational studies suggest associations between higher dietary spermidine intake and better cognitive outcomes, but do not establish causality. Randomized clinical trials to date are few, include small and heterogeneous populations, and have not demonstrated consistent effects on primary cognitive endpoints. Overall, spermidine represents a biologically plausible modulator of pathways relevant to neurodegeneration, but translation of preclinical findings into clinical benefit remains uncertain. Current evidence is insufficient to support its use as a therapeutic or preventive intervention in AD, and further well-designed clinical studies are required to clarify its efficacy and mechanisms of action. Plain Language Summary: Alzheimer’s disease is one of the most common causes of memory loss in older adults. Researchers are searching for ways to protect brain cells and slow the biological processes that lead to this disease. One molecule that has recently attracted attention is spermidine, a natural compound found in all living cells and in many foods, including whole grains, legumes, mushrooms, and aged cheeses. Spermidine plays several roles in the body. One of its most important effects is activation of autophagy, a natural cellular process that removes damaged proteins and other cellular waste. This process is relevant to Alzheimer’s disease because the condition is associated with the accumulation of abnormal proteins in the brain. Experimental studies also suggest that spermidine may influence inflammation in the brain, support mitochondrial function (the energy system of cells), and help maintain communication between nerve cells. In this review, we summarized evidence from laboratory experiments, animal studies, and available human research. In animal models of brain aging and Alzheimer’s disease, spermidine consistently shows neuroprotective effects and can improve memory performance. Human evidence is more limited. Observational studies suggest that higher dietary spermidine intake may be associated with better cognitive performance, while clinical trials investigating supplementation have produced mixed results. Spermidine is naturally present in many foods and is increasingly studied in the context of aging and brain health. Overall, current evidence suggests that spermidine may play a role in brain aging. Larger and well-designed clinical studies are needed to clarify its potential relevance for Alzheimer’s disease. The infographic highlights spermidine’s effects and mechanisms. Preclinical evidence from animal and cell models shows benefits like autophagy and mitophagy for clearing damaged proteins, improved mitochondrial function, reduced neuroinflammation, lower oxidative stress and enhanced cognition. Mechanisms include autophagy activation, mitochondrial health and proteostasis support, aiding neuronal homeostasis. Human studies suggest higher dietary spermidine intake may improve cognition, but clinical trials are small and varied, showing inconsistent effects on cognitive endpoints. Overall, human evidence is limited and inconclusive.An infographic on spermidine’s effects, mechanisms and evidence from preclinical and human studies. Keywords: spermidine, Alzheimer’s disease, autophagy, cognition, neuroinflammation, diet