Alcohol, aging, and the gut microbiome: Intersections of immunity, barrier dysfunction, and disease.

Alcohol consumption exerts complex, dose- and context-dependent effects on human health, particularly by influencing the gut microbiome, intestinal barrier integrity, immune regulation, and aging processes. Genetic variation and advancing age are two major, and often interacting, factors that modify the risk of alcohol-related diseases. Among genetic factors, the prevalent aldehyde dehydrogenase 2 polymorphism (ALDH2∗2) compromises acetaldehyde clearance, driving toxic metabolite accumulation, oxidative stress, and increased intestinal permeability that disrupts gut microbial communities, even at low levels of alcohol consumption. Heavy and chronic alcohol use further disrupts gut microbial communities, erodes mucosal integrity, and drives systemic inflammation, contributing to alcohol-associated liver disease (ALD), neuroinflammation, and multi-organ injury. Aging independently worsens these effects by promoting chronic low-grade inflammation and impaired immune responses, heightening susceptibility to alcohol-induced pathology. In specific contexts, such as certain autoimmune diseases, low to moderate alcohol intake may exert immunomodulatory effects and influence the gut microbiome, potentially contributing to reduced inflammation and alterations in microbial composition. This review synthesizes current mechanistic insights into how alcohol, host genetics, the gut microbiome, immune regulatory pathways, and aging intersect to influence disease risk. As global populations age and the burden of alcohol-related health issues rises, there is an urgent need for integrated, systems-level approaches. Future research should prioritize precision-based, gut-targeted strategies aimed at restoring microbial balance, maintaining intestinal barrier integrity, and mitigating alcohol-related harm across the lifespan.