Secular trends in prevalence of dementia and their contributing factors : Insights from the Hisayama Study

Abstract

The Hisayama Study, an ongoing community–based epidemiological study in Hisayama Town, Fukuoka Prefecture since 1961, has begun epidemiological research on dementia in 1985. We conducted seven prevalence survey of dementia covering almost all residents aged ≥65 years in 1985, 1992, 1998, 2005, 2012–2013, 2017–2018, and 2022–2023, achieving consistently high participation rates (≥92%). The crude prevalence of all–cause dementia substantially increased from 6.7% in 1985 to 17.9% in 2012. However, prevalence of dementia subsequently declined, reaching 15.6% in 2017 and 11.9% in 2022. A similar trend was seen even after adjustment for age.

Since prevalence of dementia is determined by both incidence and prognosis of dementia, we also established three cohorts in the residents aged ≥ 65 years without dementia in 1988 (n = 803), 2002 (n = 1,231), and 2012 (n = 1,519), each of which was followed for 10 years.

The age– and sex–adjusted incidence of dementia increased significantly from the 1988 to the 2002 cohort (adjusted hazard ratio [aHR] 1.68, 95% confidence intervals [CI] = 1.38–2.06), but decreased significantly from the 2002 to the 2012 cohort (aHR = 0.60, 95% CI = 0.51–0.70). The age– and sex–adjusted 5–year survival rate after dementia onset increased significantly from the 1988 to the 2002 cohort (47.3% to 65.2% ; p < 0.01), while no significant change was observed from the 2002 to the 2012 cohort (65.2% to 58.9% ; p = 0.42).

In conclusion, the decline in the prevalence and incidence of dementia in Hisayama town in recent years may be due to the prevention and improved management of lifestyle–related diseases, such as hypertension and diabetes, as well as increased awareness and promotion of healthy lifestyle behaviors.