In the United States, we lead very sedentary lifestyles. In fact, the average office worker sits for a whopping 15 hours each day. Too much sitting is correlated with weight gain and even early death, and now, it's becoming clear that the amount of time we spend sitting significantly increases dementia risk.
A new study that looked at the activity habits of 50,000 adults in the U.K. over the age of 60 found that the risk of dementia increased by 8% when people spent more than 10 hours per day sitting and jumped to 63% when people sat for 12 hours per day.
These numbers are startling and certainly make people of all ages think about how often they're sitting. But why do more hours spent sitting correlate with a higher dementia risk? Here's everything you need to know.
Understanding a Sedentary Lifestyle and Dementia Risk
Dr. Nicole Purcell, DO, MS, a neurologist with the Alzheimer's Association, says that the results of this new study are not particularly surprising. "There have been a number of studies that have previously reported an association between sedentary time and risk of dementia, including a positive meta-analysis of 18 studies going back as far as 1995," she says. "However, reports that did not find an association have also been published. Therefore, additional research on possible associations is welcome."
Unfortunately, she said, as an observational study, this current one does not establish cause and effect either. "Indeed, sedentary behaviors are associated with several risk factors for dementia, including low levels of physical activity, cardiovascular disease, diabetes, hypertension, obesity and depression," Dr. Purcell explains. "Although results remained significant after adjusting for several of these factors, further research is required to better understand the various elements that may influence the observed relationship."
However, she said, reverse causality—or the idea that changes in the brain might actually be causing the sedentary behavior—can't be ruled out. "Regular physical activity is central to your health, but even this vital component cannot be viewed in isolation," Dr. Purcell explains. "It must be considered in combination with one’s total behavior and lifestyle, including healthy diet, education, head injury, sleep, mental health, and the health of your heart/cardiovascular system and other key bodily systems."
Dr. Benjamin Emanuel, MD, an Associate Professor of Neurology at the University of Southern California Keck School of Medicine, expands on this further. "In human models, physical exercise increases gray matter (the thinking part of the brain) volume in areas that control memory and complex tasks, increases blood flow to the brain, increases a neurotransmitter that promotes brain survival and growth, improves learning and memory, attention and execution and modifies connections in the brain," he explains. "In children, exercise improves academic achievement. Thus, if someone was excessively sedentary, they would not be able to take advantage of the positive effects of physical exercise, and as a result, be at a higher risk of developing dementia compared to someone who is less sedentary."
The Habits That Increase and Increase Dementia Risk
While it's worthwhile to note that dementia is not 100% preventable, there are lifestyle habits that can increase and decrease your risk of developing it. "Other lifestyle habits that impact dementia risk include too much alcohol, tobacco use, drug use, genetics, cardiovascular disease, diet, obesity and sex," Dr. Emanuel says, noting that women are more likely to develop dementia over the course of their lifetime.
As for healthy habits that can decrease dementia risk? Exercise, obviously—but what else? "Maintaining a healthy diet, occasional alcohol consumption, avoiding tobacco and listening to your doctor are all great ways to lower the risk of dementia," Dr. Emanuel says.
Sitting Time Linked to Higher Risk of Death From All Causes. American Heart Association.
Dr. Nicole Purcell, DO, MS, a neurologist with the Alzheimer's Association
Dr. Benjamin Emanuel, MD, an Associate Professor of Neurology at the University of Southern California Keck School of Medicine