Small amounts of moderate to vigorous physical activity are associated with big reductions in dementia risk

The researchers found that engaging in as little as 35 minutes of moderate to vigorous physical activity per week, compared to zero minutes per week, was associated with a 41% lower risk of developing dementia over an average four-year follow-up period. Even for frail older adults -- those at elevated risk of adverse health outcomes -- greater activity was associated with lower dementia risks.

The researchers found dementia risk decreased with higher amounts of physical activity. Dementia risks were 60% lower in participants in the 35 to 69.9 minutes of physical activity/week category; 63% lower in the 70 to 139.9 minutes/week category; and 69% lower in the 140 and over minutes/week category.

For their analysis, the researchers analyzed a dataset covering nearly 90,000 adults living in the U.K. who wore smart-watch-type activity trackers.

The study was published online January 15 in the Journal of the American Medical Directors Association.

"Our findings suggest that increasing physical activity, even as little as five minutes per day, can reduce dementia risk in older adults," says study lead author Amal Wanigatunga, PhD, MPH, assistant professor in the Bloomberg School's Department of Epidemiology. Wanigatunga is also a core faculty member at the Johns Hopkins Center on Aging and Health and has a joint appointment at the Johns Hopkins University School of Medicine. "This adds to a growing body of evidence that some exercise is better than nothing, especially with regard to an aging-related disorder that affects the brain that currently has no cure."

Dementia, usually from Alzheimer's disease, is one of the most common conditions of old age. It is estimated to affect about seven million people in the U.S., including about a third of those who are 85 years or older. Although the risk of dementia rises with age, studies in recent years have suggested that dementia is somewhat preventable, within a normal lifespan, by lifestyle changes that include better control of cholesterol, blood pressure and blood sugar, and being more active.

The minimum amount of activity needed to reduce dementia risk meaningfully isn't yet clear. For many older individuals, especially frail ones, the high amounts of exercise recommended in official guidelines are unattainable and may discourage any exercise at all. Both the U.S. Department of Health and Human Services and the U.K. National Health System recommendthat adults get at least 150 minutes of moderate intensity exercise per week, an average of 20 minutes per day.

For their study, Wanigatunga analyzed data on British adults generated as part of the UK Biobank project, a long-running, ongoing study of approximately 500,000 individuals. The dataset for the new study covered 89,667 adults, mostly in their 50s and older, who used wrist-worn accelerometers to track their physical activity for a week during the period from February 2013 to December 2015. Follow-up of their health status extended for an average of 4.4 years, through November 2021, during which 735 of the participants were diagnosed with dementia.

The analysis compared individuals whose trackers showed some weekly moderate to vigorous physical activity to those whose trackers showed none and accounted for age and other medical conditions. The associations between higher activity and lower dementia risk were striking. Participants in the lowest activity category, ranging from one to 34.9 minutes per week, had an apparent risk reduction of about 41%.

When the researchers took into account participants who met their definitions of frailty or "pre-frailty," they found that the association between more activity and less dementia was essentially unchanged.

"This suggests that even frail or nearly frail older adults might be able to reduce their dementia risk through low-dose exercise," Wanigatunga says.

Wanigatunga notes that the study was not a clinical trial that established causation indicating that exercise reduces dementia risk, but its findings are consistent with that hypothesis. To check the possibility that their findings reflected undiagnosed dementia leading to lower physical activity, the researchers repeated their analysis but excluded dementia diagnoses in the first two years of follow-up. The association between more activity and lower dementia risk remained robust.

Wanigatunga and his colleagues recommend that future clinical trial-type studies investigate low-dose exercise as an important initial step towards increasing physical activity as a dementia-preventing strategy.

Funding for the study was provided by the National Institute on Aging (K01 AG076967, R01 AG075883).