The decline in cognitive function with age and its changes over time in cognitively normal older adults

Purpose Cognitive trajectories in older adults classified as cognitively normal are poorly characterized, and it is unclear whether their cognitive function has improved or worsened in the past 10 years, a period marked by both increasing affluence and COVID-19-related social restrictions. Methods We recruited 343 adults aged 60 years and older classified as cognitively normal at Nagoya University Hospital from 2013 to 2022. Participants were categorized into four age groups: 60s, early 70s, late 70s, and 80s. A cross-sectional analysis of covariance (ANCOVA) was conducted to identify which cognitive function tests exhibited earlier declines. To further investigate temporal trends in cognitive performance in the decade from 2013 to 2022 among individuals classifiedas cognitively normal, linear regression analyses were performed using the year of assessment as an explanatory variable. Additionally, ANCOVA was employed to compare cognitive function among cognitively normal individuals assessed during three distinct periods: 2013–2016, 2017–2019, and 2020–2022. Results Advancing age was associated with poorer performance across all neuropsychological test domains. Processing speed and executive indices declined earliest, with significant decrements evident in the early 70s. Neither linear regression nor ANCOVA using test year as an explanatory variable revealed a consistent improvement in neuropsychological test battery performance over the years; instead, a trend toward deterioration was observed. Conclusions In cognitively normal older adults, attention, processing speed, and executive abilities begin to decline in the early 70s. The cognitive function of individuals classified as cognitively normal may deteriorate year by year. A classification of “normal” cognition does not guarantee stability and should not lead to complacency.