By Sehba Husain-Krautter, MD, PhD, and Robert P. Roca, MD, MPH
Time passes and we get older. Aside from traveling at the speed of light, nothing can be done to alter that time constant. And as we age, we inevitably start to notice changes in the way we function: how fast we can run; how easily we can balance on one foot; how quickly we can process the information; how easily we can learn new things. Or as Bette Davis supposedly said, “Getting old is not for sissies.”
Of all the above changes, decreased cognitive function may be the most concerning. One of the central questions in the study of aging is to what extent the decline in cognitive functioning is caused by aging itself and to what extent it is due to diseases or patterns of disuse that simply correlate with advancing age. If disease and disuse are the main contributors, then hopefully we can alter the slope of our functional slide by taking steps to reduce our risk of disease and by using (for example, exercising) our bodies and brains.
What can be done?
This hope has been the subject of both research and popular writing. Disease prevention is an important opportunity, and there is little debate about whether brain health improves with exertion (eg, not of smoking; control blood pressure) to prevent diseases that can lead to strokes and other types of brain diseases.
And then there is the exercise. It has become commonplace to praise the benefits of exercise as a way to preserve and improve physical and mental functioning as we age. And no one is more eager to accept this notion than the co-authors of this post: a Baby Boomer and a Millennial, both geriatric psychiatrists and avid athletes.
But is this just an illusion, or a way to dispel anxiety about aging by imagining that we can control how we age?
There are several lines of research, including comparative studies done since 1975, that support the belief that exercise is important. One line of research studies large populations looking for correlations between exercise and a variety of medical and functional outcomes. And the message of many (but not all) of these epidemiological studies is that regular physical activity is associated with lower rates of cognitive decline and, in some studies, lower risk of dementia. One of the most recent studies It followed thousands of older adults without dementia for several years and found that self-reported physical activity, even at a low level, was associated with a lower risk of being diagnosed with dementia during the follow-up period. Also, the higher an individual’s activity level, the lower the risk.
This research is encouraging, but there’s a problem: While many of these studies show that people who report exercising have lower rates of cognitive decline, they don’t prove that exercise was the cause of the best results. The better results could have been the result of other factors, for example better diets or better genes. Researchers attempt to statistically correct for these confounders, but such corrections are not foolproof and therefore incorrect conclusions about causality may be drawn.
Or perhaps people with gestational conditions like Alzheimer’s disease, which begins to affect the brain long before there are obvious behavioral signs, are less likely to exercise because of subtle brain changes that make exercise unpleasant or reduce their motivation do exercise. That could also result in a correlation between exercise and brain dysfunction, but the causal arrow would point in the opposite direction.
Exercise should start in childhood
Offering some security in this regard is a recently published australian study examine cognitive function in middle age among people whose aptitude had been evaluated in childhoodlong before the potentially confounding effects of subclinical Alzheimer’s disease could appear. It turns out that those with the highest levels of fitness in childhood had the highest levels of global cognition decades later. This result supports the idea that physical fitness may benefit cognitive functioning later in life.
would reinforce confidence in the benefits of exercise if it could be shown that exercise exerts physiological effects that would be expected to improve cognition and, in fact, there is a line of research that analyzes precisely that. Of course, exercise has been shown to improve overall health, which is expected to improve brain function. More specifically, there is research showing that exercise can have direct beneficial effects on the brain at an anatomical, cellular, and molecular level.
For example, a 2020 study compare aerobic exercise with stretching in people with mild cognitive impairment showed that 12 months of aerobic training, but without stretching, resulted in a significant increase in blood flow to crucial brain regions. another study published in the journal Nature in 2021 showed that people with cognitive impairment who participated in structured exercise for six months had higher plasma levels of an anti-inflammatory molecule called clusterin. Thus, we can point to physiological pathways, for example increased blood flow to the brain and increased anti-inflammatory activity, by which exercise can benefit the brain and preserve cognition.
Even more confidence-building, however, would be prospective randomized trials showing that current exercise leads to measurable improvements in cognitive functioning, and there is a growing body of research in this regard. A recent example is a randomized study of the effects of aerobic training on cognition and a variety of physiological measures relevant to brain function in sedentary older adults. The finding was that those assigned to the exercise group (an average of 100 minutes per week of supervised moderate-intensity physical activity for 12 weeks) showed increases in cognition and brain-relevant physiological functioning that were not enjoyed by their counterparts in the group. of control.
Where does this leave us?
We know that many studies have shown statistical correlations between exercise and better cognitive functioning, but we cannot be 100% sure that exercise is the cause of this fortuitous result. That said, there is research showing pathways by which exercise might benefit the brain, and randomized clinical trials showing aerobic exercise over a period of weeks can improve cognition in older adults.
Undoubtedly, there are many outstanding questions: if exercise is good for cognition, how much and what type is better? More is better? Is there a ceiling above which there is no additional benefit, or even harm? These are just some of the questions we hope to see answered in the future. But one thing is for sure: we will both go for a run tomorrow.
