Each month, Dr. Jeffrey Sankoff looks at a recent study or body of research to talk to the researchers, explain the process behind it, and break down the findings.

This month: An overview on the intertwined benefits of exercise, sleep, and memory—which could help to offset memory issues for aging athletes. Not yet known: how intense and how much exercise.

There is a growing body of evidence that supports the value of sleep as a means of enhancing an athlete’s ability to train and perform in competition. Sleep, after all, is more than just a time when we allow our body to rest and recover from the activity of the preceding day, it is also the period when all manner of physiologic processes occur that allow for the restoration of normal functions across many systems.

Interestingly, while sleep improves exercise performance, the reverse is also true: exercise improves sleep. Studies have shown that people who exercise regularly have better sleep quality and quantity than those who do not.

One of the systems that benefits the most is the central nervous system, though exactly what goes on within the brain during sleep remains poorly understood. However, the vital importance of sleep to proper functioning of the brain is very clear. Sleep deprivation leads rapidly to disturbances in cognitive function, psychiatric problems, and if prolonged enough, even death.

Sleep researchers have also learned of the importance sleep has for the consolidation of short-term memories into long-term memories. Without adequate sleep there is impaired memory and significant deterioration in the performance of tasks that require that memory.

More recently, research has demonstrated that exercise also can improve memory, though the magnitude of the benefit remains unclear. In fact, there is a cyclical nature to the benefits of sleep and exercise such that sleep benefits exercise, exercise benefits sleep, and both benefit memory.

How exactly sleep relates to memory is still a subject of research. How exercise enhances sleep quality is also not completely understood, but studies have shown that acute exercise of moderate intensity performed during the daytime improves objective measures of sleep quality, leads to more minutes of deep sleep, and modifies the architecture of sleep in a way that may promote improved memory formation.

Dr. Marc Roig is a PhD in physiotherapy and researcher at McGill University School of Medicine in Montreal, Canada. He recently authored a paper that reviewed the evidence on this subject to summarize the current state of understanding and to generate hypotheses for additional research. “We know a lot about exercise and memory, we know a lot about sleep and memory, we know that exercise can improve sleep too,” he said. “But, we don’t know much about how exercise can affect sleep to improve memory. We just don’t know.”

One of the ways that exercise may be helpful with memory is by enhancing a specific type of brain activity during sleep. “If you exercise before you sleep, it changes your sleep architecture and increases slow brain wave activity,” he said. This is important, because when you examine the brain during sleep the areas where memory is laid down are marked by heightened activity of these slow waves. In other words, more slow wave activity means improved memory and exercise seems to improve slow wave activity. With exercise then, “sleep architecture is modified in such a way as to enhance slow wave activity and memory is enhanced,” Roig said.

There are several biochemical and physiological theories that could explain how exercise helps benefit memory in this way. Exercise raises core temperature, which results in an increase in slow brain waves. Similarly, exercise is associated with changes in heart rate and heart rate variability related to increased parasympathetic tone that again enhances slow brain wave activity.

Exercise also results in increased levels of a specific marker that originates in brain tissue and is associated with increased neuroplasticity. Brain derived neurotrophic factor (BDNF) is seen in higher concentrations when the brain is forming new connections and actively storing new information, including memories. BDNF increases after periods of exercise, suggesting another potential way that exercise and memory enhancement are linked.

Finally, exercise is associated with increased levels of several inflammatory blood markers, all of which contribute to slow brain wave activity. 

Beyond the brain activity, though, another way that exercise may improve memory during sleep is simply by improving the quality of the sleep itself. As mentioned earlier, there is a growing body of evidence to suggest that exercise improves sleep architecture, leading to more and longer periods of deep sleep. Roig notes that, “there are a lot of studies now that demonstrate that if you start having sleep problems in your 50s, you are much more likely to have cognitive problems and memory problems when you get older. Preserving quality sleep and quality sleep architecture is therefore very important, and exercise may play an important role here.”

A few questions still remain to be answered, but researchers are hopeful that what is known to date bodes well for future findings. For example, it is well established that memory and the ability to incorporate new memories declines with age. Exercise has been shown to help mitigate the effects of sleep deprivation on memory. Is it possible that, as we age, exercise might also have an impact on delaying the effects of age on memory as well? “Exercise will not prevent Alzheimer’s disease,” Roig said, “but exercise can prevent or slow the memory decline associated with mild cognitive impairment or mild Alzheimer’s seen with advancing age.”

How much of a role does regular exercise have on improving memory? Studies to date have all focused on the effects of single bouts of acute exercise. Will those who exercise regularly be found to have improved overall memory over time versus those who do not exercise regularly? Roig believes that it is possible. “My feeling is that elderly people who exercise regularly will have preserved sleep architecture similar to those who are younger and this will preserve memory longer, but we don’t know, we don’t yet have studies on this.” Volume and intensity of exercise are also likely to be important in this equation, though it remains to be determined just how much of a role these variables will have.

Roig and other researchers are eager to find the answers to these questions and will be conducting studies in an attempt to further delineate how exercise and memory are interdependent, especially for older athletes. For now, keep training, it will help you sleep better and very likely help you remember things better as well.

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