Together, these results suggest that the initiation and maintenance of physical activity across adulthood may be more important than the timing of participating in physical activity in the life course, or the frequency of physical activity at a specific period. Lifelong maintenance of physical activity is the most optimal.
We show that being physically active at any time in adulthood, and to any extent (participating at least once per month), is linked with higher later-life cognitive state; but the strongest link is for those maintaining physical activity for longer, in an accumulative manner.
Physical activity is one proposed modifiable risk factor, modestly associated with lower risk of all-cause dementia, cognitive decline and later-life cognition. While some studies indicate that physical activity in midlife or later-life is most beneficial for later-life cognition, studies often have short follow-up periods, or are at risk of reverse directionality.
Introduction
Dementia currently affects 44 million people worldwide with prevalence expected to triple by 2050.1 Potentially modifiable risk factors may confer as much as 40% of dementia risk.2 Physical activity is one proposed modifiable risk factor and is modestly associated with lower risk of all-cause dementia,3 4 cognitive decline5 and later-life cognition.6 7 However, it is yet to be established whether the timing, frequency or maintenance of physical activity across the life course confers optimal benefit on later-life cognition. While some studies indicate that physical activity in midlife or later-life is most beneficial for later-life cognition,6 7 studies often have short follow-up periods, or are at risk of reverse directionality.8 Midlife is an important period of risk exposure for cardiovascular health on later-life cognition and brain health,4 9 10 yet it is unclear if there are important, so-called ‘sensitive’, periods for physical activity exposure, or an influential role of sustained and preserved activity throughout life, on later-life cognition. Furthermore, pathways underlying the relationship between physical activity and later-life cognition are not well established. Associations observed could be explained by earlier-life confounders such as education and social class.11 12 Implicated pathways conferring causal benefits also include better cardiovascular health13 and better mental health.4 There may also be a differential effect of physical activity on cognition by genetic APOE ε4 risk status.14
Using data from the population-based 1946 British birth cohort, which has followed people born in the same week of 1946, previous studies have demonstrated beneficial effects of midlife physical activity on midlife verbal memory15 and search speed16 decline. Here, we extend this work by taking a life course approach to evaluate the effects of physical activity timing, frequency and maintenance, spanning over 30 years, with later-life cognitive function. We assess three measures of later-life cognitive function including a measure of cognitive state, verbal memory and processing speed. We further aim to investigate to what extent, these effects are explained by pathways including earlier-life influences, cardiovascular health and mental health.
To investigate the effect of timing of physical activity, we investigated the strength of associations between a range of cognitive tests at age 69 with participation in physical activity at the ages of 36, 43, 53, 60 and 69. We then investigated whether any associations observed are best explained by physical activity in specific ‘sensitive’ periods across the life course, or being physically active across multiple time periods. Finally, we tested whether associations between physical activity and later-life cognition are modified by sex or APOE-ε4; if associations are independent of a range of relevant confounders including childhood cognition, childhood socioeconomic position (SEP) and education; and potential contributory factors including cardiovascular and mental health.