Cognitive decline and Japanese culture in a cohort of older Japanese Americans in King County, WA: the Kame Project

Objectives. The prevalence of Alzheimer's disease in studies of Japanese show generally lower rates when compared with those of Caucasians. We hypothesized that among a cohort of Japanese Americans lifestyle differences would act to modify progression of the Alzheimer pathologic process over many years, resulting in a slower cognitive decline among persons whose lifestyle is more characteristically Japanese. Methods. One thousand, eight hundred and thirty-six nondemented persons were screened with the Cognitive Abilities Screening Instrument (CASI) at baseline, and 1,604 were rescreened 2 years later. Baseline questions included migration status, exposure to Japanese culture in early life and maintenance of such culture in adulthood, and other risk factors. Cognitive decline was defined as a 2-year loss of [greater than or equal to]5.15 points/100 on CASI. Results. In multivariable logistic regression, variables relating to reading, writing, and speaking Japanese, being born or having lived in Japan in early life, and having friends who are only/mostly Japanese were inversely associated with cognitive decline (odds ratios ranged between 0.28 and 0.64, with p < .05). Two factors emerged in a factor analysis of these variables. The strongest explained 49% of the variance for acculturation and loaded heavily on knowledge of the Japanese language and having spent one's early years in Japan. When this factor was dichotomized into the top 20th percentile, it predicted cognitive decline with an odds ratio of 0.12 (95% CI 0.03-0.49). Discussion. These results show that a Japanese lifestyle may decrease the risk of expressing cognitive decline over a 2-year follow-up period. Lower cardiovascular disease rates among Japanese may also predispose them to lower rates of cognitive decline. The greater social support characteristic of Japanese culture as well as the role that Japanese language and culture may play in neural connectivity during brain development and/or in mental stimulation in adult life may also explain our findings.