Ten hours of sitting amplifies the risk of dementia

A recent study led by the University of Southern California suggests that the everyday act of sitting increases the risk of dementia, especially for older adults. 

In a collaboration with the University of Arizona, the USC researchers discovered a link between prolonged sedentary behavior and a greater risk of developing dementia for adults aged 60 and above. 

Cumulative sedentary time 

Alarmingly, the experts found that the risk is amplified among older people who remain sedentary for over 10 hours a day. This figure hovers close to the average sedentary time of an American, which stands at approximately 9.5 hours daily.

A surprising finding of the study is that the frequency of breaks does not really matter. Instead, it’s the cumulative sedentary time that counts. 

“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,” explained study co-author Professor David Raichlen. 

“We found that once you take into account the total time spent sedentary, the length of individual sedentary periods didn’t really matter.”

Focus of the study

The research was focused on data from the U.K. Biobank. As part of a Biobank sub-study, over 100,000 adults wore accelerometers – devices tasked with recording movement – continually for a week. 

The participants included about 50,000 adults aged 60 and over, all of whom were dementia-free at the study’s inception.

How the research was conducted 

To analyze this massive dataset, the researchers used machine learning to distinguish between varying intensities of physical activity. This produced an objective view of the time individuals allocated to different types of sedentary behaviors.

Over the next six years, 414 of the initial participants were diagnosed with dementia. Factoring in variables like age, sex, education level, race, and several lifestyle attributes, the research team narrowed down their results.

What the researchers discovered 

“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 co-author Gene Alexander, an expert 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.”

Study implications 

The current study expands upon prior research that explored how specific sedentary actions, such as watching TV, might influence dementia risk more than others. 

“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,” said Raichlen.

Further research is needed to establish causality and whether physical activity can mitigate the risk of developing dementia, the authors said.

The research is published in the journal JAMA.

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