Association between daily sleep duration and the risk of incident dementia according to the presence or absence of diseases among older Japanese individuals in the New Integrated Suburban Seniority Investigation (NISSIN) project

•Participants both with and without diseases who had a short sleep duration were more likely to experience incident dementia.•Participants with diseases and longer daily sleep duration had the greatest HR for incident dementia.•Participants with diseases had an increased risk of incident dementia, even among individuals with moderate sleep duration.