This "Ask The Expert" is courtesy of Barbara Phillips, MD, MSPH, FCCP.
Exercise of any sort has generally been shown to improve daytime sleepiness. This is true for just about every population that has been studied, from healthy teens who took up running to inactive people who began pilates. In understanding how exercise can result in such a positive effect on sleepiness, it’s helpful to take a look at the most common causes of sleepiness.
Among the most frequent causes of sleepiness and fatigue in the population are depression, obesity, diabetes, smoking, and inadequate sleep at night. Exercise helps with the first three of these. For example, physical activity has been shown to help depression in some studies. Physical activity is also an important part of most effective weight loss programs. Working out may also help with glucose control in diabetes. So part of the beneficial effect of exercise on sleepiness may result from its positive effects on some of the common causes of sleepiness.
Another part of the story is that many conditions associated with sleepiness (including obesity, diabetes, short sleep duration and even sleep apnea) are associated with increased levels of substances known as inflammatory markers. (There are many of these, including C-reactive protein, tissue necrosis factors, and interleukins). These substances circulate in the blood and may cause sleepiness. Exercise has been shown to reduce levels of these agents, which may explain part of its effect on sleepiness. (By the way, these inflammatory markers are also associated with cardiovascular disease; part of the mechanism by which exercise reduces the risk of heart disease may be by reducing the circulating levels of inflammatory markers).
We probably don’t know the whole story yet, but what we do know is compelling: exercise can help with excessive sleepiness.