Contextual Associations of Interregional Income Gap with Physical Constitution and Dietary Environment in Individual Housebound Elderly

BACKGROUND: Much attention has been directed towards the issue of health inequalities associated with Japan’s widening income gap. Focusing on the housebound elderly, we assessed the contextual associations of the interregional income gap with body mass index (BMI). METHOD: A total of 15,200 housebound elderly living in 46 of the country’s 47 prefectures, except for Tokyo, were interviewed face-to-face using a questionnaire that covered age, gender, height, weight, medical history, utilization of nursing care, family, source of income, food consumption, and physical activity. To determine the relationship between BMI and the above-mentioned items, a linear regression analysis was performed. In the multilevel analysis, we assumed a prefecture-level random intercept on the basis of the data on the average income per capita in the 46 prefectures. RESULTS: Valid responses without missing data were obtained from 10,226 respondents (response rate: 67.3%) and used for the analyses; females accounted for 78.5% (n=8,027) of the sample. In the multilevel analysis, prefectural average income showed a significant contextual negative association with BMI in females (-0.846; P=0.001). CONCLUSIONS: Prefectural average income has a significant negative contextual association with individual-level BMI for females; females with a low rate of going out have lower BMI; and females living with children have higher BMI. Social environment may be correlated with BMI in the older population.