Have you ever had a particularly hard workout, maybe on a really hot day, and not been able to fall asleep that night? Well, knowing how intense exercise can affect the gut and in turn the immune system, it’s not a far stretch to grasp how the two can affect sleep – too much of a good thing can cause problems.
Low to moderate levels of exercise have been shown to improve just about everything health related in humans. It’s when exercise becomes more intense that the water gets murky and the health benefits are less clear (see the latest on exercise and heart health). Sleep and intense exercise does not appear to be any different.
We know that during intense or long periods of exercise the gut can become more permeable, or “leaky.” This process can lead to endotoxemia and in turn a cascade of inflammation (heat, poor nutrition, NSAIDs all increase this effect). Blood markers of inflammation are found to be elevated during this process. Studies have demonstrated that administration of higher levels of these inflammatory proteins can disrupt NREM sleep and increase wakefulness, whereas lower levels appear to improve sleep.
The mechanism by which these inflammatory markers affect sleep is thought to be related to their influence on the hypothalamic-pituitary-adrenal (HPA) axis, which helps mediate the body’s response to stress. It has also been shown that there are receptors for these proteins in the brain. So it appears the inflammatory proteins exert their effects both in a direct (central neurons) and indirect (HPA axis) manner.
Although, the exact progression of these events is not entirely clear it does appear likely that intense levels of exercise, including duration, can affect sleep through the disruption of gut integrity. This emphasizes the need to maintain optimal gut health through proper nutrition and recovery from exhaustive exercise.
Another mechanism being investigated involves the microbes of the gut and their influence on the brain and specific functions like sleep. We already know that these little bugs even release their own hormones like GABA and serotonin! There is no doubt that exciting research is currently being done on these mechanisms and we can’t wait to see what kind of impact it will have on athletes and training – stay tuned!