Summary: Adults over 60, who engage in more than 10 hours of sedentary behavior daily, have a heightened risk of dementia. The study revealed that the pattern of sedentary behavior throughout the day mattered less than the total hours spent. Using objective accelerometer data from over 50,000 participants of the U.K. Biobank, the findings after six years pinpointed 414 dementia cases. Importantly, sitting times below 10 hours daily did not indicate increased risk.
The average American is sedentary for about 9.5 hours a day, close to the 10-hour threshold found in the study.
The study employed wrist-worn accelerometers, worn 24/7 for a week, to objectively measure and classify behaviors of around 50,000 adults over 60.
After adjusting for various demographics and lifestyle characteristics, dementia risk began to surge after 10 hours of daily sedentary time.
Adults aged 60 and older who spend more time engaging in sedentary behaviors like sitting while watching TV or driving may be at increased risk of developing dementia, according to a new study by USC and University of Arizona researchers.
Their study showed the risk of dementia significantly increases among adults who spend over 10 hours a day engaging in sedentary behaviors like sitting — a notable finding considering the average American is sedentary for about 9.5 hours each day.
The study, published on Tuesday, September 12 in JAMA, also revealed the way sedentary behavior is accumulated over the course of the day didn’t matter as much as the total time spent sedentary each day.
Whether spent in extended periods spanning several hours or spread out intermittently throughout the day, total sedentary behavior had a similar association with dementia according to study author David Raichlen.
“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 used data from the U.K. Biobank, a large-scale biomedical database of participants across the United Kingdom, to investigate possible links between sedentary behavior and dementia risk.
As part of a U.K. Biobank sub-study, over 100,000 adults agreed to wear accelerometers, wrist-worn devices for measuring movement, for 24 hours per day for one week. The researchers focused on a sample of approximately 50,000 adults from this sub-study over the age of 60 who did not have a diagnosis of dementia at the start of the study.
The researchers then applied a machine-learning algorithm to analyze the large dataset of accelerometer readings and classify behaviors based on different intensities of physical activity.
The algorithm was able to discern between different types of activity such as sedentary behavior versus sleeping. The accelerometer data, combined with advanced computing techniques, provided researchers with an objective measure of the time spent engaging in different types of sedentary behaviors.
After an average of six years of follow-up, the researchers used inpatient hospital records and death registry data to determine dementia diagnosis. They found 414 cases positive for dementia.
Then, the team adjusted their statistical analysis for certain demographics (e.g., age, sex, education level, race/ethnicity, chronic conditions, genetics) and lifestyle characteristics (physical activity, diet, smoking and alcohol use, self-reported mental health) that could affect brain health.
Total time spent sedentary each day drives dementia risk
While high amounts of sedentary behavior were linked with increased risk of dementia, the researchers found that there were certain amounts of sedentary behavior that were not associated with 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 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.
The study builds on their previous research, which used self-reported health data to investigate how certain types of sedentary behavior, like sitting and watching TV, affect 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.
More research is needed to establish causality and whether physical activity can mitigate the risk of developing dementia, the authors said.
About the study
In addition to Raichlen and Alexander, other authors of the study include Daniel H. Aslan, M. Katherine Sayre, Mark H.C. Lai and Rand R. Wilcox of USC; Pradyumna K. Bharadwaj, Madeline Ally and Yann C. Klimentidis of the University of Arizona; and Silvio Maltagliati of the Université of Grenoble Alpes, France.
Funding: The study was supported by grants P30AG072980, P30AG019610, R56AG067200, R01AG064587 and R01AG072445 from the National Institutes of Health and funding from the state of Arizona, the Arizona Department of Health Services and the McKnight Brain Research Foundation. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
About this dementia research news
Author:Nina Raffio Source: USC Contact: Nina Raffio – USC Image: The image is credited to Neuroscience News
Sedentary Behavior and Incident Dementia Among Older Adults
Sedentary behavior is associated with cardiometabolic disease and mortality, but its association with dementia is unclear.
To investigate whether accelerometer-assessed sedentary behavior is associated with incident dementia.
Design, Setting, and Participants
A retrospective study of prospectively collected data from the UK Biobank including 49 841 adults aged 60 years or older without a diagnosis of dementia at the time of wearing the wrist accelerometer and living in England, Scotland, or Wales. Follow-up began at the time of wearing the accelerometer (February 2013 to December 2015) and continued until September 2021 in England, July 2021 in Scotland, and February 2018 in Wales.
Mean daily sedentary behavior time (included in the primary analysis) and mean daily sedentary bout length, maximum daily sedentary bout length, and mean number of daily sedentary bouts (included in the secondary analyses) were derived from a machine learning–based analysis of 1 week of wrist-worn accelerometer data.
Main Outcome and Measures
Incident all-cause dementia diagnosis from inpatient hospital records and death registry data. Cox proportional hazard models with linear and cubic spline terms were used to assess associations.
A total of 49 841 older adults (mean age, 67.19 [SD, 4.29] years; 54.7% were female) were followed up for a mean of 6.72 years (SD, 0.95 years). During this time, 414 individuals were diagnosed with incident all-cause dementia. In the fully adjusted models, there was a significant nonlinear association between time spent in sedentary behavior and incident dementia.
Relative to a median of 9.27 hours/d for sedentary behavior, the hazard ratios (HRs) for dementia were 1.08 (95% CI, 1.04-1.12, P < .001) for 10 hours/d, 1.63 (95% CI, 1.35-1.97, P < .001) for 12 hours/d, and 3.21 (95% CI, 2.05-5.04, P < .001) for 15 hours/d. The adjusted incidence rate of dementia per 1000 person-years was 7.49 (95% CI, 7.48-7.49) for 9.27 hours/d of sedentary behavior, 8.06 (95% CI, 7.76-8.36) for 10 hours/d, 12.00 (95% CI, 10.00-14.36) for 12 hours/d, and 22.74 (95% CI, 14.92-34.11) for 15 hours/d.
Mean daily sedentary bout length (HR, 1.53 [95% CI, 1.03-2.27], P = .04 and 0.65 [95% CI, 0.04-1.57] more dementia cases per 1000 person-years for a 1-hour increase from the mean of 0.48 hours) and maximum daily sedentary bout length (HR, 1.15 [95% CI, 1.02-1.31], P = .02 and 0.19 [95% CI, 0.02-0.38] more dementia cases per 1000 person-years for a 1-hour increase from the mean of 1.95 hours) were significantly associated with higher risk of incident dementia.
The number of sedentary bouts per day was not associated with higher risk of incident dementia (HR, 1.00 [95% CI, 0.99-1.01], P = .89). In the sensitivity analyses, after adjustment for time spent in sedentary behavior, the mean daily sedentary bout length and the maximum daily sedentary bout length were no longer significantly associated with incident dementia.
Conclusions and Relevance
Among older adults, more time spent in sedentary behaviors was significantly associated with higher incidence of all-cause dementia. Future research is needed to determine whether the association between sedentary behavior and risk of dementia is causal.