2 Ways Cardio Workouts May Help Aging Brains Stay Healthy

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Although there's some debate about whether or not staying physically active without breaking a sweat can improve cognitive performance during midlife, a growing body of evidence suggests that, as we age, regular aerobic exercise training (AET) at a moderate-to-vigorous level of intensity keeps healthy amounts of blood pumping through the brain and may help to offset cognitive decline.

Does Every Type of Physical Activity Improve Cognitive Outcomes?

This week, a two-decade study (Greendale et al., 2021) of almost 2,000 middle-aged women, with an average age of 45.7 years at baseline, was published in JAMA Network Open. The UCLA-led team of researchers who conducted this longitudinal study found that "self-reported physical activity was not associated with measured cognitive performance in the domains of processing speed, verbal memory, or working memory."

These findings challenge the notion that staying physically active during midlife has neuroprotective benefits. As the authors conclude, "[Our] findings suggest that the cognitive protection effect of physical activity observed in later life may be an artifact of reverse causation."

Before jumping to conclusions, it's worth noting that this "longitudinal assessment of physical activity and cognitive outcomes among women at midlife" has some limitations.

"Our study showed that in midlife, women's usual, self-selected exercise activity was not sufficient to slow cognitive aging," first author Gail Greendale said in a news release. However, she also points out: "This study does not tell us whether increasing physical activity to higher levels might help preserve cognitive function."

Arthur Kramer wrote an invited commentary, "How to Better Study the Associations Between Physical Activity, Exercise, and Cognitive and Brain Health," that accompanied this March 31 JAMA Open Network paper. Kramer offers three ways that he believes the "researchers should consider modifying their experimental approach" and concludes:

"In closing, the study by Greendale et al. offers a number of important advances in the observational study of the associations between physical activity (PA) and cognition in terms of sample diversity, a multitude of assessments over an extended time period, and a relatively thorough self-reported measure of PA. However, to continue to resolve discrepancies in the literature and to further increase our understanding of the associations and mechanisms of PA and cognitive health, improvements in how we study these associations are possible and warranted."

"We need more research on how to prevent cognitive aging during middle age—we just don't know what works," Greendale said in the news release. "In the meantime, the benefits of physical activity are great. While we work to figure out whether exercise is good for your brain, it's important that we strive to maximize physical activity throughout the lifespan."

Moderate-to-Vigorous Aerobic Exercise Increases Cerebral Blood Flow; Gentle Stretching Doesn't

Coincidentally, another peer-reviewed study (Tomato et al., 2021) published last week in the Journal of Alzheimer's Disease—that was featured in a New York Times article by Gretchen Reynolds on March 31, 2021—pinpoints two specific ways that moderate-to-vigorous aerobic exercise (e.g., brisk walking) "is good for the aging brain."

The objective of this year-long study by researchers at the University of Texas Southwest Medical Center in Dallas was "to investigate the effects of aerobic exercise training on central arterial stiffness and cerebral blood flow (CBF) in patients with amnestic mild cognitive impairment (MCI), a prodromal stage of Alzheimer's disease."

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For this proof-of-concept, randomized controlled trial, the researchers assigned one group of amnetic MCI patients aged 55-80 to a one-year regimen of moderate-to-vigorous aerobic exercise three to five times per week for 30-40 minutes; a control group was assigned to do stretching-and-toning exercises (without cardio) for the same duration of time.

After one year of monitoring both groups, the researchers concluded that doing about a half-hour of aerobic exercise 3-to-5 times per week at a moderate-to-vigorous intensity "reduced central arterial stiffness and increased cerebral blood flow." Notably, the stretch-and-tone group didn't reap the same brain benefits.

"Those who performed aerobic exercise showed decreased stiffness of blood vessels in their neck and increased overall blood flow to the brain," the researchers explain in a March 23 news release. "The more their oxygen consumption (one marker of aerobic fitness) increased, the greater the changes to the blood vessel stiffness and brain blood flow. Changes in these measurements were not found among people who followed the stretching program."

Although this one-year study didn't find significant improvements to study participants' episodic memory and executive functions based on standard neuropsychological tests (CVLT-II and D-KEFS), the researchers speculate that these benefits may take more time. "Changes to blood flow could precede changes to cognition," the authors said.

"Having physiological findings like this can also be useful for physicians when they talk to their patients about the benefits of exercise," senior author Rong Zhang concluded. "We now know, based on a randomized, controlled trial, that exercise can increase blood flow to the brain, which is a good thing."

Of Note: This 2021 study by Zhang and colleagues is a follow-up to research he conducted last year (Binu et al., 2020) that identified a link between moderate-to-vigorous physical activity (MVPA) and increased CBF. (See, "The Brain-Boosting Benefits of Exercise and Cerebral Blood Flow.")

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