The Impact of Sleep, Physical Activity, and Sedentary Behavior on Dementia Risk
Post by Leanna Kalinowski
The takeaway
Three modifiable daily behaviors – sleep, physical activity, and sedentary behavior – independently and collectively impact dementia risk by influencing brain structure.
What's the science?
Dementia, defined as a loss of cognitive functioning that is severe enough to interfere with daily life, does not yet have an effective treatment despite its increased prevalence. Previous research has determined that three modifiable daily behaviors – sleep, physical activity, and sedentary behavior – are associated with the risk of developing dementia. Specifically, sleep deprivation and lack of physical activity are likely to exacerbate brain atrophy, defined as the loss of neurons in the brain. However, research on these associations is limited and based on relatively small numbers of study participants. This week in Molecular Psychiatry, Huang and colleagues investigated the impact of sleep duration, physical activity, and sedentary behavior on dementia risk and brain structure.
How did they do it?
The researchers used data from 431,924 participants in the UK Biobank study, which is a large-scale biomedical study that has been collecting data in the United Kingdom since 2006. At baseline, participants were asked several questions about sleep duration, physical activity, and sedentary behavior, and underwent structural MRI scans. All participants underwent a follow-up assessment an average of nine years after baseline.
To measure sleep duration, participants were asked how many hours of sleep they get per night and were divided into three categories: low sleep (0-6h), moderate (7h), and high sleep (8+h). To measure leisure-time physical activity, participants were asked to describe the frequency and duration of different activities undertaken over the previous four weeks. These activities were then converted into their metabolic equivalents (MET), which is the resting metabolic rate obtained during quiet sitting. After summing total MET for all physical activities, physical activity was divided into three categories: low (<400 MET/week), moderate (400-1200 MET/week), and high (>1200 MET/week). Finally, to measure sedentary behavior, participants were asked to report the number of hours spent watching TV and using a computer during a typical day. Sedentary behavior was then divided into three categories: low (0-2h/day), moderate (>2-4h/day), and high (>4h/day).
What did they find?
When measured independently, sleep, physical activity, and sedentary behavior were each associated with dementia risk. When compared to those in the moderate sleep category, both those in the low and high sleep categories demonstrated an increased dementia risk. In terms of physical activity, the risk of dementia dropped with every MET increase up until 1200 MET/week, above which there was little additional benefit of physical activity. As for sedentary behavior, there was no increased risk of dementia until the rate of sedentary behavior exceeded 3h/day, at which point the risk of dementia increased exponentially as the number of hours/day of sedentary behavior increased.
Taking each measurement together, the researchers found that a combination of moderate sleep, moderate-to-high physical activity, and low-to-moderate sedentary behavior showed the lowest risk of dementia. Structural MRI scans from these individuals showed larger cortical and subcortical grey matter volumes, suggesting that these activities impact dementia risk by affecting the structure of the brain.
What's the impact?
This study was the first of its kind to examine the independent and joint effects of sleep, physical activity, and sedentary behavior on the development of dementia. Findings from this study provide important insights into different risk factors for dementia and highlight the importance of changing these behaviors to reduce dementia risk.