BACKGROUND: The COVID-19 pandemic may have negatively impacted cognition due to pandemic-associated changes in 24-h movement behaviours (i.e., physical activity, sedentary behaviour, and sleep). Whether the pandemic's effects vary by age and sex is unclear. METHODS: We examined those participants (aged 45-85 years) of the Canadian Longitudinal Study on Aging (CLSA) with complete neuropsychological measures at baseline (2011-2015), no dementia/memory disorder, and partial or complete assessments at baseline, 3-year (FU1
2015-2018), and 6-year follow-up (FU2
2018-2021). Participants were categorized into pre-pandemic (N = 6174) or intra-pandemic (N = 5181) cohorts by FU2 assessment timing (before/after March 11th, 2020) and stratified by baseline age/sex. Cognition was measured with reliable change indices using: the Rey Auditory-Verbal Learning Test, Mental Alternation Test (MAT), and animal fluency. We indexed physical activity and sedentary behaviour using the Physical Activity Scale for the Elderly (PASE), and self-reported restless sleep. FINDINGS: Compared with their pre-pandemic peers, intra-pandemic men aged 65-85 years had lower animal fluency (-0.40 points, 99 % CI: [-0.72, -0.07]), lower PASE (-16.48 points, 99 % CI: [-24.60, -8.36]) and 14 % higher probability of ≥4 h/day sedentary behaviour (99 % CI: [0.03, 0.26]) at FU2. Intra-pandemic women aged 65-85 years had lower MAT (-0.43 points, 99 % CI: [-0.86, -0.01]) and 12 % higher probability of ≥4 h/day sedentary behaviour (99 % CI: [0.01, 0.23]). There were no between-cohort differences for those aged 45-64 years. Pandemic-related changes in 24-h movement behaviours (FU1 to FU2) were not associated with cognitive changes, regardless of age or sex. INTERPRETATION: The pandemic's effects on cognition and 24-h movement behaviours varied by age and sex
these effects are unrelated.