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

Cognitive trajectories in older adults classified as cognitively normal are poorly characterized, and it is unclear whether their cognitive function has improved or worsened over the past decade, including the COVID-19 pandemic.

We recruited 343 adults aged ≥ 60 years who visited a memory clinic with various complaints, including subjective or objective memory problems, but were classified as cognitively normal after comprehensive evaluations by specialists between 2013 and 2022. Participants were categorized into four age groups: 60 s, early 70 s, late 70 s, and 80 s. 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 from 2013 to 2022, linear regression analyses were performed using the year of assessment as an explanatory variable. Additionally, ANCOVA was employed to compare cognitive function during three distinct periods: 2013-2016, 2017-2019, and 2020-2022.

Advancing age was associated with poorer performance across all cognitive domains. Processing speed and executive indices declined earliest, with significant decrements evident in the early 70 s. Neither linear regression nor ANCOVA using test year revealed any improvement in neuropsychological test performance; instead, significant deterioration across multiple domains was observed.

In cognitively normal older adults, attention, processing speed, and executive abilities begin to decline in the early 70 s. The cognitive function of individuals classified as cognitively normal may deteriorate over time. These findings highlight that a diagnosis of "normal cognition" in a memory clinic does not ensure long-term cognitive stability.