While being sedentary is harmful for all age groups, a new study showed older adults who keep seated for more than 10 hours a day watching TV may be at an increased risk of developing dementia.

The study, published in JAMA, revealed that a sedentary lifestyle with a lot of sitting and lying down, with very little to no exercise accumulated over the course of the day didn’t matter as much as the total time spent sedentary each day.

According to study author David Raichlen from University of South California (USC), total sedentary behaviour had a similar association with dementia, whether spent in extended periods spanning several hours or spread out intermittently throughout the 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 Raichlen, Professor of biological sciences and anthropology at the USC Dornsife College of Letters, Arts and Sciences.

Researchers analysed 50,000 adults over the age of 60 who did not have a diagnosis of dementia at the start of the study.

The participants wore accelerometers for 24 hours per day for one week and the team used machine-learning to read and classify behaviours based on different intensities of physical activity.

The accelerometer data, combined with advanced computing techniques, provided researchers with an objective measure of the time spent engaging in different types of sedentary behaviours.

After an average of six years of follow-up, the researchers used inpatient hospital records and death registry data to determine dementia diagnosis and found 414 cases positive for dementia.

“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 behaviour and dementia risk, but importantly lower levels of sedentary behaviour, up to around 10 hours, were not associated with increased risk,” said Gene Alexander, Professor of psychology and psychiatry at the University of Arizona.

“This should provide some reassurance to those of us with office jobs that involve prolonged periods of sitting, as long as we limit our total daily time spent sedentary,” added Raichlen.