A pathway from low socioeconomic status to dementia in Japan: results from the Toyama dementia survey.

BACKGROUND: The association between low socioeconomic status (SES) and dementia is reportedly mediated by lifestyle-related diseases (i.e., diabetes) in European countries and the United States; however, in Japan, the link between low SES and dementia has not been investigated. This study evaluated the possibility of a mediating role of lifestyle-related diseases in the relationship between low SES and dementia in Japan.

METHODS: A retrospective case-control study design, with data from the Toyama Dementia Survey, Japan, was used. Individuals aged ≥65 years (institutionalized and noninstitutionalized) living in Toyama prefecture were randomly selected, with a sampling rate of 0.5%. Of them, 1303 agreed to participate (response rate 84.8%). Overall, 137 cases of dementia and 1039 unimpaired controls were identified. Structured interviews with participants and family members or proxies were conducted, if necessary. Participants' history of medically diagnosed disease, lifestyle factors (i.e., smoking and alcohol drinking habits), and SES (educational attainment and occupational history) were assessed. The possibility of low SES being a risk factor for dementia via lifestyle-related diseases was investigated using the Sobel test.

RESULTS: The odds ratio (OR) for dementia was higher for participants with low educational attainment (6 years or less) than for highly educated participants [age- and sex-adjusted OR 3.27; 95% confidence interval (CI) 1.84-5.81]; it was also higher for participants with a blue-collar job history than a white-collar job history (age- and sex-adjusted OR 1.26; 95% CI 0.80-1.98). After adjustment for employment history, the OR for dementia for participants with low educational attainment was 3.23-3.56. Former habitual alcohol consumption and a medical history of diabetes, Parkinson's disease, stroke, and angina pectoris/cardiovascular disease were found to increase the risk of dementia. Educational attainment was not associated with alcohol consumption, smoking, diabetes, Parkinson's disease, stroke, or cardiovascular disease. Occupational history was associated with diabetes and stroke. The role of diabetes in low educational attainment and dementia was found to be extremely limited.

CONCLUSIONS: In Japan, lifestyle-related diseases play a minimal role as mediators between low SES and dementia.