OP64 Joint associations of physical activity and sleep duration with cognitive ageing: longitudinal analysis of an English cohort study

Background

As there is currently no effective treatment for dementia, it is important to identify contributors to cognitive decline from midlife to delay onset of clinical symptoms. Lack of physical activity (PA) and nightly sleep duration outside 6–8 hours are interrelated factors thought to contribute to cognitive decline and dementia risk. Nonetheless, how PA and sleep combine to influence trajectories of cognitive ageing is not well-explored, with the majority of evidence coming from cross-sectional studies. As PA and sleep behaviours can be impacted by preclinical dementia symptoms, this poses a considerable limitation to causal inference in previous studies. To investigate interacting roles of PA and sleep in cognitive ageing, we examined longitudinal associations of different combinations of PA and sleep duration with 10-year cognitive trajectories.

Methods

Linear mixed models were used to examine independent and joint associations of PA (low, high) and sleep duration (short [<6 hours], optimal [6–8 hours], long [>8 hours]) with cognitive performance at baseline, 10 years, and cognitive decline in adults aged ≥50 years from the English Longitudinal Study of Ageing (N=8991). We excluded respondents with evidence of cognitive impairment in order to reduce bias due to reverse causation. Models were adjusted for sociodemographic and socioeconomic covariates, health behaviour indicators, chronic conditions, and depressive symptoms.

Results

Low PA was independently associated with worse cognitive performance at baseline (p<0.001), while short sleep was independently associated with faster cognitive decline (p=0.04). At baseline, high PA/optimal sleepers had higher cognitive scores than all sleep categories in the low PA category (e.g. difference high PA/optimal-low PA/optimal at age 50=0.10 [0.06, 0.15] standard deviations), while there was no difference in cognitive performance between sleep categories within the high PA category. Differences remained consistent over 10 years of follow-up, except high PA/short sleepers who declined faster than high PA/optimal sleepers, such that their cognitive scores at 10 years were commensurate with those in the low PA category (difference high PA/optimal-high PA/short=0.20 [0.05, 0.34]; high PA/optimal-low PA/short=0.28 [0.15, 0.41]).

Conclusion

PA and sleep duration combine in complex ways to influence cognitive trajectories from middle age; for example, the cognitive benefit at baseline provided by high PA was insufficient to blunt the more rapid cognitive decline associated with short sleep. While WHO already identify PA as a target for maintaining cognitive function, effective PA interventions should also consider sleep habits to maximise potential benefits of PA for cognitive health and delay onset of dementia.