Small doses of exercise can greatly reduce dementia risk

A small weekly dose of moderate to vigorous exercise – just 35 minutes – could significantly lower an older adult’s chances of developing dementia, according to a new study.

Led by the Johns Hopkins Bloomberg School of Public Health, the research found that even older people who are frail appear to benefit from this low level of activity.

The results suggest that physical activity is an accessible way for many seniors to protect their cognitive health.

Reducing dementia risk with exercise

The researchers analyzed data from nearly 90,000 adults living in the United Kingdom. Each participant wore a wrist-based device that recorded their physical activity for a week, and they were then followed over an average period of 4.4 years to see who developed dementia.

The findings were striking: compared to participants who recorded zero moderate-to-vigorous physical activity, those who achieved as little as 35 minutes per week had a 41% reduced risk of being diagnosed with dementia. 

Greater amounts of physical activity correlated with even lower risks: 60% lower for 35–69.9 minutes, 63% lower for 70–139.9 minutes, and 69% lower for 140 or more minutes.

Study lead author Amal Wanigatunga is an assistant professor of epidemiology at the Bloomberg School. 

“Our findings suggest that increasing physical activity, even as little as five minutes per day, can reduce dementia risk in older adults,” explained Wanigatunga.

“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 risks and the role of exercise

Dementia, often caused by Alzheimer’s disease, is highly prevalent among older populations – about seven million individuals in the United States alone. One in three people over the age of 85 is affected, and the numbers are expected to rise as the population ages.

Scientists have long studied how lifestyle factors might reduce dementia risk, pointing to better management of cholesterol, blood pressure, and blood sugar, alongside increased physical activity. However, it has been less clear how small or large an exercise dose should be to help protect the brain. 

Current guidelines in both the U.S. and the U.K. recommend 150 minutes of moderate-intensity exercise each week (roughly 20 minutes per day). While beneficial, that target may intimidate some older adults – particularly those who are frail or limited by mobility issues.

The new data suggest that even a fraction of the recommended time could deliver meaningful protection against dementia. The researchers took special note of participants who met criteria for “frailty” or “pre-frailty” and found that low volumes of exercise were associated with lower dementia risk in those groups as well. 

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

Study limitations and future directions

Because this study was not a clinical trial, it cannot conclusively prove that exercise itself prevents dementia. 

To reduce the possibility of reverse causation – i.e., that undiagnosed dementia caused people to move less – the team repeated their analysis after excluding dementia diagnoses that occurred in the first two years of follow-up. 

The protective link between activity and lower dementia risk remained strong, adding credibility to the idea that movement itself helps preserve cognitive function.

The authors call for additional research to confirm these results through randomized clinical trials. They see “low-dose” exercise as a potentially critical step for seniors – especially those who struggle to meet higher targets. 

By encouraging just a few minutes per day and building up gradually, more people might achieve at least 35 minutes of moderate or vigorous activity per week and thus lower their odds of cognitive decline.

Dementia risk in older adults

These findings are particularly relevant given the growing number of older adults worldwide and the significant impact dementia can have on individuals, families, and healthcare systems. 

Although some may find it difficult to dedicate 20 minutes each day to exercise, the study demonstrates that even small increments of movement – brief walks, light gardening, or gentle workouts – can add up to better brain health.

For now, the message is clear: a little bit of exercise is better than none at all, and that small effort might yield substantial rewards. 

By broadening access to physical activity for older adults – especially those who feel constrained by frailty – health practitioners could take an important step toward reducing the burden of dementia in an aging society.

The study is published in the Journal of the American Medical Directors Association.

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