Age-Related Cognitive Decline and Dementia: Interface of Microbiome–Immune–Neuronal Interactions

The microbiome plays a critical role in both promoting human health and contributing to diseases. Multiple emerging evidence shows that it contributes to aging and cognitive decline; however, the mechanisms are not fully understood. Changes in the microbiome and immune system occur with age, and immune functions are one of the key mechanisms linking the microbiome to the brain. Disrupted immunological balance may lead to neuroinflammation and blood-brain barrier dysfunction, contributing to cognitive decline. However, comprehensive knowledge regarding the types of microbiome and immune interactions influencing neuronal and cognitive health in aging remains largely unknown. This review presents evidence about the types of microbiome alterations associated with healthy versus unhealthy aging and how they interact with immune cells linked to neuronal and cognitive functions. It also explores whether and how microbiome modulators like probiotics, prebiotics, and postbiotics can be potential interventions to help preserve cognitive function in older adults.