The study also revealed that the way sedentary behavior is accumulated over the day didn’t matter as much as the total amount of time spent being sedentary each day, whether that time is spent in extended periods or spread out intermittently, total sedentary behavior had a similar association with dementia according to the researchers. These findings are alarming given that the average American is sedentary for around 9.5 hours a day.
“Many of us are familiar with the common advice to break up long periods of sitting by getting up every 30 minutes or so to stand or walk around. We wanted to see if those types of patterns are associated with dementia risk. We found that once you take into account the total time spent sedentary, the length of individual sedentary periods didn’t really matter,” said study author David Raichlen, professor of biological sciences and anthropology at the USC Dornsife College of Letters, Arts, and Sciences.
For this study, the researchers utilized data from over 100,000 adults who were enrolled in the U.K. Biobank, who agreed to wear accelerometers to measure their movements 24 hours a day for one week. The team focused on a sample of 50,000 adults over the age of 60 from this subgroup who were not diagnosed with dementia at the beginning of the study period.
Deep machine-learning algorithms were then applied to analyze the accelerometer readings and classify behaviors based on different levels of physical activity. The algorithm was able to distinguish different levels of activity such as sleeping and sedentary behaviors to provide an objective measure of time spent engaging in different types of behaviors.
In-patient hospital records and national death registry data were used to determine dementia diagnosis, and after an average of six years of follow-up, the researchers found 414 cases that were positive for dementia. The team adjusted their statistical analysis for a range of demographics, factors, and lifestyle characteristics that might affect brain health. According to the researchers, high levels of sedentary behavior were linked with an increased risk of dementia, but certain amounts of sedentary behavior were not associated with dementia. However, it was noted that additional research is required to establish causality and whether physical activity can mitigate the risk.
“We were surprised to find that the risk of dementia begins to rapidly increase after 10 hours spent sedentary each day, regardless of how the sedentary time was accumulated. This suggests that it is the total time spent sedentary that drove the relationship between sedentary behavior and dementia risk, but importantly lower levels of sedentary behavior, up to around 10 hours, were not associated with increased risk,” said study author Gene Alexander, professor of psychology and psychiatry at the Evelyn F. McKnight Brain Institute at the University of Arizona and Arizona Alzheimer’s Disease Research Center.
“This should provide some reassurance to those of us with office jobs that involve prolonged periods of sitting, as long we limit our total daily time spent sedentary,” said Raichlen. “Our latest study is part of our larger effort to understand how sedentary behavior affects brain health from multiple perspectives. In this case, wearable accelerometers provide an objective view of how much time people dedicate to sedentary behavior that complements our past analyses.”
