The news on Alzheimer’s disease doesn't paint a pretty picture. As the population ages, there will a tidal wave of cases, or so the standard narrative goes. Meanwhile, drug trial after drug trial fails. Early diagnosis is still in its infancy, and even if it improves, there's no treatment—and thus not much hope for those diagnosed.
Is this negative picture accurate, and is there anything we can do to avoid such a future?
Rethinking the Disease
Many of the risk factors for Alzheimer’s disease are essentially the “usual suspects” for cardiovascular disease. These include diabetes, high blood pressure, and physical inactivity. In fact, Alzheimer’s has been described as “type 3” diabetes.
The good news: The things we do while we are young and middle-aged to stay healthy are almost certainly helping our brains. How does this work?
Building a Strong Brain
A key concept is “cognitive reserve," the idea that changes associated with Alzheimer’s disease don’t always correlate with symptoms. People with “strong brains” can overcome the structural changes caused by Alzheimer’s disease without much decline in cognitive performance.
Cognitive reserve also explains why things like education, ongoing intellectual pursuits, and physical activity are protective against dementia. People who do things that keep their brains healthy have more robust brain connections and as a result:
..more efficient utilization of brain networks or enhanced ability to recruit alternate brain networks as needed...
The parallels with sports performance are striking. Start at a higher baseline through training and keep practicing over time and you can adapt to aging without much fall-off in performance.
Why Exercise Matters
One reason diabetes is such a big problem is that it can essentially trash small blood vessels throughout the body, including those in the brain. When you add high blood pressure to the mix, it is the classic double hit and things go from bad to worse.
However, several new studies show that while brain blood flow goes down with aging, the decline is slower in people who are fit. More importantly, the ability of the brain vessels to essentially “open up” via a process called vasodilation is preserved in fit older people. In a study conducted in my own lab we concluded that:
Cerebral vasodilator responses to hypercapnia (carbon dioxide) were associated with maximal aerobic capacity in healthy older adults. These results may explain the physiological link between regular aerobic exercise and improved cognitive function in aging adults.
Growing New Nerve Cells
The standard teaching used to be that sometime relatively early in life the structure of the brain was more or less fixed, and it was all downhill from there. However, newer evidence indicates that the brain can continue to essentially rewire itself throughout life in response to new challenges. There is also evidence that hormones and other chemical messages released during exercise can stimulate this rewiring.
Humans are among the most mobile species known and this mobility requires us to be able to rapidly adapt to changing environments. One theory explaining the link between activity and new nerve cell connections is that:
Changing places requires flexibility, and doing so at increased speed over prolonged periods of time (as found in tribal and modern endurance runners, or wheel-running or freely roaming rodents, if one wants to follow this argument) requires optimized pattern separation. The observation that a generic stimulus such as physical activity should stimulate a type of brain plasticity that is relevant for complex cognition—an observation that is perhaps counterintuitive at first glance—might thus be explained by this testable theory.
The Bottom Line
For most of us, some cognitive decline as we age is probably inevitable, but there is no reason to be fatalistic about a full-blown descent into dementia and Alzheimer’s. Staying physically and mentally active and continuing to try new things works. What we do when we are young and as we age is the key to being the mythical active and fit 85-year-old-uncle at the family reunion who can still instigate with the kids!
Michael J. Joyner, M.D., is a physiologist and anesthesiologist at the Mayo Clinic and a leading voice in the world of exercise physiology. Over the past 25-plus years, he's published hundreds of studies, many of which have focused on how humans respond to exercise. Dr. Joyner also writes at Human Limits. The views expressed in his posts are his own and do not reflect those of his employer.