Lifestyle and environmental risk factors for adult-onset autoimmune diabetes: current evidence and future directions.

Adult-onset autoimmune diabetes encompasses both classical type 1 diabetes and latent autoimmune diabetes in adults (LADA), which differ in their metabolic features and rates of progression to insulin deficiency. While autoimmune diabetes frequently develops during adulthood, potential modifiable risk factors remain largely unexplored. This review summarises current evidence on lifestyle and environmental factors associated with adult-onset autoimmune diabetes. Overweight, obesity and smoking emerge as the most consistent risk factors for both adult-onset type 1 diabetes and LADA. Evidence from observational and Mendelian randomisation studies supports a role for adiposity and smoking in increasing disease risk, potentially through reduced insulin sensitivity, which may accelerate progression from islet autoimmunity to overt diabetes. Moreover, individuals carrying high-risk HLA genotypes appear more susceptible to adverse effects of adiposity and smoking. Dietary factors have primarily been studied in LADA, with increased risk observed in relation to sugar-sweetened beverages and processed red meat, and reduced risk associated with fatty fish, n-3 fatty acids and moderate alcohol consumption. A few, partly contradictory, studies point to protective roles of vitamin D and vitamin E in LADA and adult-onset type 1 diabetes. Other exposures implicated in childhood-onset disease, including viral infections and psychosocial stress, remain largely unexplored in adults. However, the evidence base remains limited and largely restricted to populations of European ancestry. Large prospective studies with long follow-up and detailed phenotyping from different populations of diverse ancestry are needed to identify causal risk factors and inform prevention strategies.