Low socioeconomic status as a major risk factor for early-onset type 2 diabetes with limited lifestyle mediation: Cross-Sectional evidence from US and South Korean populations.

This study aimed to examine the association between socioeconomic status (SES) and early- and late-onset type 2 diabetes (T2D), evaluate the mediating role of a healthy lifestyle in these associations, and further explore the contribution of various risk factors to different types of T2D. This study analyzed data from US NHANES, and Korean KNHANES, encompassing 20,655 US, and 26,575 Korean adults. SES was categorised as high, middle, or low based on income, education, employment, and insurance. A healthy lifestyle score included nonsmoking, no heavy drinking, regular physical activity, and a high-quality diet. Early-onset T2D was defined as diagnosis before age 40. In NHANES, early-onset T2D prevalence was 1.35 %, rising from 0.85 % (high SES) to 2.41 % (low SES); late-onset prevalence was 5.63 %, with similar SES gradients. Comparable patterns emerged in KNHANES. Low SES consistently increased the risk of early-onset T2D, with stronger associations observed compared to late-onset T2D. A healthy lifestyle only mediated the relationship between SES and late-onset T2D. In early-onset T2D, a healthy lifestyle did not have a significant protective effect. The strength of the associations between the risk factors for early-onset T2D was generally greater than that for late-onset T2D, especially for obesity and family history of diabetes. Low SES is a stronger risk factor for early-onset T2D, with lifestyle interventions proving insufficient to mitigate risk. Public health efforts should prioritize addressing social determinants, early screening, and targeted education for vulnerable youth, particularly those with low SES, obesity, or a family history of diabetes.