You need not be an Ironman to have a strong and sharp brain.
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Did you know the most popular New Year's resolution year after year is to exercise more? While that's a valiant goal, more is not always better—especially if you set such a lofty goal that you can't stick with it … and subsequently feel like a failure and quit trying.

But you might not need to focus on going from 0 to 100 to benefit your body and your brain. Lightly active adults reduced their risk for dementia by a sizable 20% after a 3½ year follow-up compared to their inactive peers, according to a study published December 16 in the journal JAMA Network Open.

This echoes the findings of a study released earlier this year that found walking just three times per week could reduce dementia risk and builds on 2019 research that suggested 10 minutes of moderate-intensity exercise per day could protect against cognitive decline. So, what exactly does light physical activity look like? According to this study, it's as light as walking at a slow or leisurely pace.

There's no cure (yet) for dementia and its most common type, Alzheimer's disease. So doctors are hustling to determine which lifestyle habits may reduce the risk or at least delay the onset of dementia.

For this study, a team of Korean researchers tapped into medical records in the Korean National Health Insurance Service database for 62,286 participants who were 65 or older and who had not yet received a dementia diagnosis. The individuals were about 60% women and 40% men, with an average age of 73. Each person recorded his or her physical activity including frequency, intensity and duration of exercise via a self-reported questionnaire. After 3½ years, on average, the researchers followed up and found that 6% of the participants had developed dementia.

Using these reports, the researchers split the group into levels: inactive, insufficiently active, active and highly active. In terms of dementia risk, after accounting for age, sex and other diseases, they found:

  • Inactive participants were the baseline
  • Insufficiently active participants were at 10% lower risk for dementia
  • Active participants were at 20% lower risk for dementia
  • Highly active participants were at 28% lower risk for dementia

That means even a little bit can go a long way in terms of exercise's bang for your brain buck. (Btw, those activity levels are based on one recommendation for ideal physical activity level: 500 to 999 metabolic equivalent task minutes (or MET minutes) per week. For more on what MET minutes are, check out our piece about whether it's better to sleep in or exercise when you're tired.)

Moving from sedentary to just some "light-intensity physical activity is associated with metabolism, and this vascular, cellular and metabolic change by light-intensity physical activity could be beneficial in reducing dementia risk," Boyoung Joung, M.D., a professor of internal medicine at Yonsei University College of Medicine in Seoul, Republic of Korea, and the study's corresponding author tells Medical News Today.

That said, this study cannot prove any causal link. In other words, are people who are likely to develop dementia naturally less active because they're already experiencing some mild symptoms? Or could other factors be at play and the exercise rates just be a coincidence—or misreported, since these were questionnaires that could be fibbed on?

"The idea that physical activity reduces the risk of dementia is entirely plausible, and these findings add to a growing body of evidence supporting this idea," John Gallacher, Ph.D., director of Dementias Platform UK at Oxford University, tells Medical News Today. "The problem is reverse causation—that is, that people with dementia exercise less. This study goes some way to addressing this by looking at incident events and dropping subjects with incident dementia in the first 2 years of follow-up."

Physical activity could trigger metabolism changes, improve overall chronic disease risk factors, slow cell aging and promote brain plasticity, though, so it's possible this could be a causal relationship. More research is needed, though.

"All these arguments apart, the balance of risk is that exercise is good for you, and a little goes a long way," Gallacher adds.

Health experts believe that more than 1 in 3 dementia cases can be prevented through lifestyle modifications and, in the future, researchers hope to dedicate time to longer-range studies with more breakouts in terms of exercise styles, time and beyond.

For now, it's still wise to lace up those shoes and sneak in a walk, bike ride, dance session or yoga routine with a goal of working up to 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity exercise per week, per World Health Organization guidelines.