BACKGROUND: Social networks and social participation have protective effects on cognitive function maintenance and Alzheimer's disease and general dementia development.

OBJECTIVE: We aimed to investigate the association between conversations and dementia incidence in older adults.

METHODS: This longitudinal prospective cohort study used population data from the National Center for Geriatric and Gerontology-Study of Geriatric Syndromes (NCGG-SGS) from September 2015 to February 2017. The database included 4,167 individuals in Japan aged ≥60 years who were generally healthy and without major cognitive impairment. Participants were classified into two groups according to six daily conversation measures at baseline. The conversation index was calculated as a composite score for these measures. Participants were tracked monthly over 60 months for new-onset dementia.

RESULTS: Data from 2,531 participants were analyzed (72.7±6.7 years; range: 60-96 years). Dementia incidence per 1,000 person-years was 15.7 (95% confidence interval, 13.6-18.1). The Youden index determined the cut-off point for dementia incidence, with a conversation index of 16/17 points. The low conversation group included more participants with new-onset dementia. Cox proportional hazards regression crude models showed remarkable relationships between dementia onset and specific conversation measurements, including conversation index. According to the Cox regression adjusted model, the cut-off point of the conversation index showed only a remarkable relationship with dementia onset.

CONCLUSIONS: Dementia risk was extensively associated with low daily conversation statuses. The assessment of conversational factors may be useful as a risk indicator for the development of Alzheimer's disease and general dementia.