Longitudinal relationships between subjective fatigue, cognitive function, and everyday functioning in old age

Background: The present study examined the prospective relationships between subjective fatigue, cognitive function, and everyday functioning. Methods: A cohort study with secondary data analysis was conducted using data from 2,781 community-dwelling older adults without dementia who were enrolled to participate in the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) randomized intervention trial. Measures included demographic and health information at baseline, and annual assessments of subjective fatigue, cognitive function (i.e. speed of processing, memory, and reasoning), and everyday functioning (i.e. everyday speed and everyday problem-solving) over five years. Results: Four distinct classes of subjective fatigue were identified using growth mixture modeling: one group complaining fatigue some of the time at baseline but most of the time at five-year follow-up (increased fatigue), one complaining fatigue a good bit of the time constantly over time (persistent fatigue), one complaining fatigue most of the time at baseline but some of the time at five-year follow-up (decreased fatigue), and the fourth complaining fatigue some of the time constantly over time (persistent energy). All domains of cognitive function and everyday functioning declined significantly over five years; and the decline rates, but not the baseline levels, differed by the latent class of subjective fatigue. Except for the decreased fatigue class, there were different degrees of significant associations between the decline rates of subjective fatigue and all domains of cognitive function and everyday functioning in other classes of subjective fatigue. Conclusion: Future interventions should address subjective fatigue when managing cognitive and functional abilities in community-dwelling older adults.