Incidence of dementia diagnosis in Denmark, 1986-2023: an age-period-cohort analysis

Denmark is experiencing unprecedented population ageing, highlighting the importance of understanding age-related diseases, including dementia. Dementia is a syndrome characterised by progressive decline in cognitive function that interferes with daily activities and independent living. This study quantifies changes in dementia diagnosis across ages, time periods, and birth cohorts in Denmark. Using Danish registry data from 1986 to 2023, we analysed all individuals aged 50 and older, corresponding to the birth cohorts 1886-1973. We conducted an age-period-cohort analysis and stratified by sex. Dementia diagnosis was measured by either: 1) hospitalisation for dementia via ICD codes; or 2) filling at least two prescriptions for a dementia-related drug. Dementia diagnoses increased with age across cohorts and periods. The age effect showed rates beginning to rise around age 75 and peaking in the late 80s and early 90s. Looking at the period effect, incidence rates begin to increase in 1997 when the first dementia-related drugs became available, followed by a decrease in later years. Younger cohorts showed lower dementia incidence rates compared to older cohorts at similar ages, likely due to changes to modifiable risk factors. Findings from this study contribute to understanding dementia risks on the age, period, and cohort levels, and can inform public health policies aimed at diagnosing cognitive decline and improving quality of life for older populations.