Incidence of dementia among individuals 70 years and older in Norway: A HUNT study

BackgroundWith increasing population longevity, Alzheimer's disease and dementia have become a health priority, and high-quality incidence estimates are needed.ObjectiveTo provide reliable and precise incidence estimates of dementia applying a population-based sample of individuals aged 70+.MethodsA longitudinal cohort design was used, with baseline assessment in the Norwegian HUNT4 70+ study (2017-19) and at follow-up four years later (2021-23). Age-specific dementia incidence rates, standardized for the Norwegian population, were calculated as the number of new dementia cases per 1000 person-years assuming onset midway between study waves with inverse probability weights based on baseline factors associated with non-participation or death.ResultsAmong 5229 dementia-free individuals at baseline, 749 developed dementia over a 4.2-year period, resulting in a cumulative incidence proportion of 14.3%. At follow-up, 33.8% of new dementia cases showed no baseline cognitive impairment, while the rest had mild cognitive impairment (MCI). Of those with baseline MCI, 25.5% reverted to normal cognition, 48.2% remained MCI, and 26.2% developed dementia. The dementia incidence per 1000 person-years, was 43.9 (95% confidence interval (CI) 40.8, 47.1) (weighted for non-response and standardized to the dementia-free Norwegian population).ConclusionsOur study found higher dementia incidence rates in the 70+ population than hospital records indicate. Most individuals had preceding MCI, with similar numbers reverting to normal cognition as developing dementia. The projected incident dementia cases suggest a near doubling between 2023 and 2050, significantly impacting families and healthcare planning, including early detection and interventions.