Age-Related Cognitive Decline and Prevalence of Mild Cognitive Impairment in the Iwaki Health Promotion Project

Background: The Iwaki Health Promotion Project (IHPP) is a community-based study for the prevention of lifestyle-related diseases and improvement of quality of life. Objective: Between 2014 and 2017, a total of 4,442 Iwaki town residents from 19 to 93 years of age participated in annual surveys to clarify the natural course of age-related cognitive decline and mild cognitive impairment (MCI). Methods: Modified OLD and SED-11Q questionnaires, MMSE, Logical Memory II, educational history, and APOE genotypes were examined at the first screening. MCI and dementia were diagnosed at the second examination by detailed neurological examination, CDR, and MRI, and followed for 3 years. Spline regression analyses based on a linear mixed model was adopted for statistical analysis. Results: MMSE scores declined with age from 55 to 64 years. There was also interaction between levels of education and ages. At the second examination, 56 MCI and 5 dementia patients were identified. None of the MCI cases progressed to dementia during the 3 years. During follow-up examinations, 13 cases showed improved MMSE scores (0.95 point/year), 5 remained stable, and 7 deteriorated (-0.83 point/year). Five cases showed improved CDR-SOB scores (-0.28 point/year), 9 remained stable, and 6 deteriorated (0.3 point/year). Conclusion: IHPP revealed that age- and education-related cognitive decline began and advanced from 55 years of age. The prevalence of MCI and dementia was estimated to be 5.9% in the Iwaki town cohort over 60 yeas of age. About 30% of MCI cases showed progression of cognitive decline.