The runner's high has long been attributed to endorphins. These are chemicals produced naturally in the body of humans and other animals after exercise and in response to pain or stress.
Health benefits of exercise
Several decades of research has shown that exercise is beneficial for physical health. These studies find a consistent link between varying amounts of physical activity and reduced risk of premature death and dozens of chronic health conditions, including diabetes, hypertension, cancer, and heart disease.
More recently – over about the past two decades – mounting research shows that exercise is also highly beneficial for mental health. In fact, regular exercise is associated with lower symptoms of anxiety, depression, Parkinson's disease, and other common mental health or neurological problems.
Consistent exercise is also linked to better cognitive performance, improved mood, lower stress, and higher self-esteem. This is where our research and that of others points to the role of our body's natural versions of cannabinoids, called endocannabinoids.
The surprising role of endocannabinoids
You may be familiar with cannabinoids such as tetrahydrocannabinol – better known as THC – the psychoactive compound in cannabis (from the Cannabis sativa L. plant) that causes people to feel high. Or you may have heard of cannabidiol, commonly known as CBD, an extract of cannabis that is infused in some foods, medicines, oils, and many other products.
But many people do not realize that humans also create their own versions of these chemicals, called endocannabinoids. These are tiny molecules made of lipids – or fats – that circulate in the brain and body; "endo" refers to those produced in the body rather than from a plant or in a lab.
endocannabinoids circulating in the blood, some have reported inconsistent findings, or that different endocannabinoids produce varying effects.
We also don't know yet if all types of exercise, such as cycling, running, or resistance exercise like weightlifting, produce similar results. And it is an open question whether people with and without preexisting health conditions like depression, PTSD or fibromyalgia experience the same endocannabinoid boosts.
To address these questions, an undergraduate student in my lab, Shreya Desai, led a systematic review and meta-analysis of 33 published studies on the impact of exercise on endocannabinoid levels.
We compared the effects of an "acute" exercise session – like going for a 30-minute run or cycle – with the effects of "chronic" programs, such as a 10-week running or weightlifting program. We separated them out because different levels and patterns of exertion could have very distinct effects on endocannabinoid responses.
We found that acute exercise consistently boosted endocannabinoid levels across studies. The effects were most consistent for a chemical messenger known as anandamide – the so-called "bliss" molecule, which was named, in part, for its positive effects on mood.
Interestingly, we observed this exercise-related boost in endocannabinoids across different types of exercise, including running, swimming, and weightlifting, and across individuals with and without preexisting health conditions.
Although only a few studies looked at intensity and duration of exercise, it appears that moderate levels of exercise intensity – such as cycling or running – are more effective than lower-intensity exercise – like walking at slow speeds or low incline – when it comes to raising endocannabinoid levels.
This suggests that it is important to keep your heart rate elevated – that is, between about 70 and 80 percent of age-adjusted maximum heart rate – for at least 30 minutes to reap the full benefits.
There are still a lot of questions about the links between endocannabinoids and beneficial effects from exercise. For example, we didn't see consistent effects for how a chronic exercise regimen, such as a six-week cycling program, might affect resting endocannabinoid levels.
Likewise, it isn't yet clear what the minimum amount of exercise is to get a boost in endocannabinoids, and how long these compounds remain elevated after acute exercise.
Despite these open questions, these findings bring researchers one step closer to understanding how exercise benefits brain and body. And they offer an important motivator for making time for exercise during the rush of the holidays.
Originally published in The Conversation