The ‘key windows’ when exercise may matter most for brain health

By Kristen Rogers, CNN

(CNN) — Scientists have hailed the benefits of exercising early in life to lower the risk of your brain degenerating later. But new research suggests that even once you’re 45 or older, it’s not too late to try.

Having the highest levels of physical activity in midlife and late life was associated with a 41% and 45% lower risk of dementia, respectively, found the study that published November 19 in the journal JAMA Network Open. Midlife was defined as ages 45 to 64, while late life was ages 65 to 88.

“This study shifts the conversation from ‘exercise is good for the brain’ to ‘there may be key windows when exercise matters most for brain health,’” said Dr. Sanjula Singh, an instructor in neurology at Harvard Medical School and principal investigator at the Brain Care Labs at Massachusetts General Hospital in Boston. She wasn’t involved in the study.

With an estimated 57 million people worldwide having dementia and nearly triple that number expected by 2050, the authors “wanted to investigate whether the impact of physical activity on dementia risk differed or stayed consistent across the adult life course,” said Dr. Phillip Hwang, lead study author and assistant professor in the department of epidemiology at Boston University School of Public Health, via email.

A downside of this study is that it can’t suggest how much exercise to do due to the measurement the researchers used, Hwang said. It was “a composite measure based on the number of hours a person spends sleeping, in sedentary behavior, and doing light, moderate and heavy activities in a day,” he added. “However, finding ways to be more active and moving around is important.”

Hwang’s findings are also affirmed by other studies that suggested more specific guidance. A 2022 study found that people who walked just 3,800 steps per day lowered their risk of dementia by 25%, and, generally, the more steps participants walked, the greater the benefits were. Using a bike instead of a car, bus or train for transportation has been linked with a 19% lower risk of dementia and a 22% reduced risk of Alzheimer’s disease.

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“Given what is already known about the benefits of physical activity on other conditions — such as the heart, mood, stress, etc., which are also related to the brain and cognition — there are lots of other reasons as well to be more active,” Hwang said via email.

Adults need at least 150 to 300 minutes of moderate aerobic activity or 75 to 150 minutes of vigorous aerobic exercise per week, according to the World Health Organization.

Such exercise could be, for example, 150 minutes of brisk walking, 75 minutes of vigorous running or cycling, and strength training a couple of times per week, Singh said. Singh is part of the team that developed the Brain Care Score, a 21-point assessment of how a person fares on physical, lifestyle, social and emotional factors they can change to protect their brain health.

If you’re new to exercise, begin with slower or shorter workouts, then gradually increase intensity, said Dr. Raphael Wald, a neuropsychologist with Marcus Neuroscience Institute at Baptist Health South Florida. “Starting too aggressively can lead to orthopedic injuries, which may then limit your ability to exercise at all,” Wald added via email.

Build consistent habits that can help ensure you stay active daily, Wald said, such as walking for 20 minutes before work or taking a short movement break during lunch.

Tracking activity and dementia risk

The new study’s findings are based on 1,526 participants in early adult life — ages 26 to 44 — nearly 2,000 middle-age adults and nearly 900 older adults who were mostly White and part of the long-term Framingham Heart Study.

Physical activity levels in early adult life weren’t associated with dementia risk in either direction, the authors found. They also discovered that even for older adults who had the strongest genetic risk factor for Alzheimer’s disease — the APOE ε4 gene — high physical activity was still linked with a 66% lower risk of dementia.

The study has important limitations, experts said. “People who are more active may also engage in other healthy behaviors, have better baseline health, or differ in ways the researchers couldn’t fully measure,” Singh said.

The team acknowledged that it didn’t have details on middle- and older-age adults’ physical activity levels in their early adult lives or how habits changed over time, which could also influence risk for dementia. Participants may also misjudge their levels, so studies with tracker wearables would be a more objective way to measure exercise, Singh said.

Midlife and late life possibly being extra critical for brain health may be explained by a few factors, experts said.

“Exercise plays a major role in maintaining vascular health,” Wald said. “The most common vascular risk factors — high blood pressure, type 2 diabetes, thyroid disease and high cholesterol — tend to emerge in midlife and later adulthood. It makes sense that exercise during these periods would have the greatest impact on reducing dementia risk.”

Physical activity is also thought to lower dementia risk by improving brain structure and function, alleviating inflammation and slowing the buildup of beta-amyloid proteins in the brain, Hwang said. The latter is a hallmark sign of Alzheimer’s disease.

If you’re reconsidering your fitness habits and other risk factors for dementia, Wald said, remember that maintaining balance and talking to your doctor about all the factors involved are essential.

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