The Independent and Joint Effects of Physical Activity and Sedentary Behavior on Dementia and Cognitive Decline
Open AccessBackground: Cognitive impairment and dementia, which is cognitive impairment to the point that it interferes with daily function, are prevalent among older adults and are associated with serious health and socioeconomic consequences. Physical activity has been identified as a promising avenue for preventing or delaying cognitive decline, but only represents one component of an individual’s daily movement. Sedentary behavior is another potential factor, but there is a dearth of evidence regarding the relationship between sedentary behavior and cognitive function and dementia in the literature. This is particularly true for different types of sedentary behavior, including both cognitively stimulating and non-cognitively stimulating activities performed while seated. The joint associations of physical activity and sedentary behavior with cognitive function and dementia have been even less studied. Aims and Methods: This research employed secondary data analysis to examine whether and how sedentary behavior and physical activity were associated with dementia and cognitive function, as assessed by the Teng Min-Mental State (3MS), Digit Symbol Substitution Test (DSST), and CLOX 1, in participations responding to the Health, Aging and Body Composition (Health ABC) Study. The first aim examined the independent and combined associations of physical activity and sitting time with future odds of dementia. Physical activity (kcal/week) and sitting time (hours/day) were self-reported in 1999-2000 and dementia status was evaluated from June 1, 2001 through September 30, 2014. Multivariable logistic regression evaluated the independent and joint associations of physical activity and sitting time with odds of dementia. The second aim examined the associations of different types of sedentary behavior and 3-year change in the time spent on those activities with cognitive function and dementia. Multivariable linear regressions was used to examine associations between baseline sitting, TV watching, and reading time – and change in those behaviors – with cognitive function test scores. Multivariable logistic regression evaluated associations between change in sitting, TV, and reading time with odds of dementia. Results: For Aim 1, sedentary behavior and physical activity were not independently or jointly associated with odds of dementia. In the independent associations model, neither being in the high sitting group (9+ hours/day; OR=0.94, 95% CI=0.72, 1.23) nor being in the low physical activity group (<500 kcal/week; OR=1.06, 95% CI=0.79, 1.42) were associated with greater odds of dementia. In the joint associations model, participants in the high sitting and low physical activity group did not have a greater odds of dementia compared with participants in the low sitting and high physical activity group (OR=1.16, 95% CI=0.74, 1.82). For Aim 2, more reading time at baseline was associated with a 0.09-point (SE=0.03, p<0.05) higher 3MS score and a 0.14-point (SE=0.04, p<0.01) higher DSST score. An increase in TV watching time between 1999-2000 and 2002-2003 was associated with a 1.53-point (SE=0.72, p<0.05) decrease in 3MS score. Conclusion: This research adds to the evidence base related to daily movement and cognitive function and dementia among older adults. The relationship among these variables is complex and difficult to study, particularly because some types of sedentary behavior may have benefits for cognitive function in older adults, outweighing the potential harms associated with lack of movement. More research is needed to explicate whether and how daily movement affects and/or reflects cognitive function, including dementia, among older adults.
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