Individual- and neighborhood-level factors influencing diet quality: a multilevel analysis using Korea National Health and Nutrition Examination Survey data, 2010-2019.

Although environmental factors influence lifestyle choices, few studies have examined how individual- and neighborhood-level sociodemographic factors interact to affect diet quality in Korea. We investigated the associations between multilevel factors and diet quality among Korean adults and explored potential interactions by gender and age. We conducted a cross-sectional analysis of 42,035 adults from 1,671 towns using data from the Korea National Health and Nutrition Examination Survey (2010-2019) and the Population and Housing Census of Korea (2010-2019). Individual-level variables included gender, age, education, income, number of household members, smoking, drinking, physical activity, and subjective health status. Neighborhood-level variables included residential area, housing type, number of restaurants per capita, population size, and the proportion of low-income households and older adults. Associations with the Korean Healthy Eating Index (KHEI) were assessed using 2-level hierarchical models. Of the total variance in KHEI, 5.2% was attributable to neighborhood-level differences. Individual-level factors explained 48.1% of variance at the neighborhood level, while neighborhood-level factors accounted for an additional 12.4%. Individuals living in rural areas, non-apartment housing, neighborhoods with higher proportions of low-income households and older adults, or in areas with smaller populations, had lower KHEI scores than their counterparts. In random slope models with cross-level interaction terms, diet quality among adults aged 70 years and older varied significantly according to neighborhood-level characteristics. Both individual- and neighborhood-level factors influence diet quality in Korea, with older adults being especially vulnerable to neighborhood characteristics. Multilevel approaches are needed to identify at-risk populations and improve dietary outcomes.