October 4, 2023
Older men and women who sat for more than 10 hours a day had a higher risk of developing Alzheimer’s disease and other forms of dementia, according to a new report. The study found that adults 60 and older who spent many hours in sedentary activities like sitting, driving or watching TV were more likely to develop dementia over the next six or seven years than their peers who spent less of their day sitting.
It was less important whether sedentary adults got up and walked periodically to break up their inactivity. Rather, it was the total amount of time spent sitting during the day that had the biggest impact on Alzheimer’s risk.
“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,” said study author David Raichlen of the University of Southern California. “We found that once you take into account the total time spent sedentary, the length of individual sedentary periods didn’t really matter.”
Sedentary behavior has long been linked to an increased risk of heart disease and other health problems. These findings build on earlier evidence suggesting that physical inactivity is also bad for the brain.
For the study, researchers looked at 49,841 men and women who were in their 60s, 70s and older. All were part of the UK Biobank, a large storehouse of ongoing health and lifestyle information of people living in England, Scotland or Wales. None had Alzheimer’s disease or other forms of dementia at the start of the study.
To gauge their level of physical activity, participants wore activity trackers on their wrists for 24 hours a day over the course of a typical week. The accelerometer devices could distinguish between activities such as sitting, moving about or sleeping.
The researchers recorded the overall time participants spent sitting in a typical day. They then reviewed their medical records over the next six to seven years. During that time, 414 of them had developed Alzheimer’s disease or other forms of dementia.
The more time someone spent sitting — past the threshold of 10 hours a day — the greater their dementia risk. It didn’t matter whether someone spent 10 hours a day sitting at one stretch, or whether the time spent sitting was broken up into several periods during the day. It was the total time spent sedentary that was important.
The researchers considered other factors that may impair brain health, such as advancing age, other illnesses such as diabetes or depression, smoking and alcohol use. Sitting more than 10 hours a day was independently associated with increased dementia 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,” said study author Gene Alexander of the University of Arizona. “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.”
The findings provide some reassurance to those who have office jobs and must sit for many hours a day. You may have to sit at a desk for eight hours a day, but as long as you keep your overall daily sedentary time to under 10 hours, you likely will not be at increased risk for Alzheimer’s disease.
The study shows only an association between being sedentary and increased dementia risk and cannot prove cause and effect. The researchers were also unable to assess whether physical activities like walking or running can counter the risk of developing dementia, though numerous earlier studies have found that regular exercise, even if its moderate, may lower the risk of developing Alzheimer’s disease by up to a third.
Earlier research from some of the same researchers also suggested that not all sitting is the same when it comes to brain health. Older men and women who sit for long periods of time doing passive activities like watching TV, for example, were at higher risk of developing dementia. People who engaged in cognitively stimulating activities like using a computer, doing crossword puzzles, doing crafts or reading a book or magazine, on the other hand, were at lower risk of dementia. So even if you do sit a lot, find mentally challenging activities that you enjoy. Your brain may thank you years down the road.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D. Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: David A. Raichlen, PhD; Daniel H. Aslan, MS; M. Katherine Sayre, PhD; et al: Sedentary Behavior and Incident Dementia Among Older Adults. JAMA September 12, 2023
