Three-year trajectories in Functional Limitations and Cognitive Decline among Dutch 75+ year olds, using nine-month intervals

Background: Using longitudinal panel data, the aim of this study was to first identify three-year trajectories in cognitive and physical functioning among Dutch older adults. And second, to identify which main characteristics were associated with these trajectories. Methods Group-based Trajectory Modelling with mortality jointly estimated was used to identify trajectories, using a scale composed of 6 Activities of Daily Living (ADL) as a measure of physical functioning, and a short version of the mini mental status examination (sMMSE) or the IQCODE as a measure of cognitive functioning. Data came from 574 Dutch adults aged 75+, collected in five nine-month measurement waves conducted between 2015 and 2018 for the Longitudinal Aging Study Amsterdam. Results Five trajectories in physical functioning were identified: ‘high’, ‘moderate’, ‘steeply declining’, ‘gradually declining’, and ‘continuously low’. People that were older, lower educated, living in an institution, or suffered from diabetes or cerebrovascular accidents were more likely to follow a low or declining physical trajectory. For cognitive functioning four trajectories were identified: a ‘high’, ‘moderate’, ‘declining’, and ‘low’ trajectory. Old age, low education, living in an institution, and heart- and lung diseases were associated with continuously low or declining cognitive functioning. Mortality risks were highest among those experiencing the continuously low functioning trajectories. Conclusions This study identified trajectories comparable to previous studies that used longer time intervals, showing the consistent presence of heterogeneity in both physical and cognitive trajectories. Co-modelling mortality resulted in bigger group sizes for the more adverse trajectories. The favourable trajectories, containing most of the participants, were mostly characterized by absence of disease, whereas trajectories showing decline did not share a common indicator. Specific chronic diseases were associated with different rates of decline, however there was no factor that was associated with all declining trajectories; future research could focus on finding such an indicator.