What Is Cortisol, And Should You Be Worried About It?

Twenty years ago, the average person did not know what cortisol was. Today, cortisol is as familiar to most of us as other hormones such as insulin and testosterone. To say that the average person has a full and accurate understanding of cortisol’s nature and functions in the human body would be a stretch, however.

In the lay public, cortisol is known as a “stress hormone” that is bad for the body. While it is true that the body does release cortisol in response to various kinds of stress, it is important to recognize that our body’s ability to respond to stress is critical to our health and survival. Even the improvements in physical fitness that we get through training are a form of stress response. Cortisol’s effects on the body are fundamentally beneficial except when we are subjected to too much stress. Then it becomes too much of a good thing. But, of course, cortisol is not exceptional in this regard.

Cortisol is produced by the adrenal gland. Its release is controlled by the hypothalamus, which is a major controller of metabolism located in the brain. One of the main jobs of cortisol is to increase the glucose concentration in the blood to make more energy readily available to the muscles. As you might expect, cortisol release from the adrenal gland increases at the onset of exercise and remains elevated throughout exercise, when the muscles create a great demand for energy.

The normal effects of cortisol are evanescent. Stress occurs, cortisol is released to make energy available, stress ceases, cortisol release goes down, and the body goes back to its normal homeostatic state. But when stress becomes chronic, as it is for so many of us today, the body is continually exposed to high levels of cortisol and long-term negative health effects may occur. Chronically elevated cortisol levels have been linked to problems including abdominal fat gain, cognitive decline, and compromised immune function. The link between cortisol and weight gain especially — which has been overblown in some quarters, but is real — has caused the hormone to acquire a bad reputation within the past decade.

Because some of the highest cortisol surges occur during and after exercise, endurance athletes are exposed to more cortisol than even many of the most stressed-out non-athletes. But do these repeated short bursts of cortisol release really add up to long-term high cortisol exposure in runners and other endurance athletes? A 2011 study says yes.

German researchers used a novel technique of measuring cortisol levels in hair to quantify cortisol levels over time in a group of endurance athletes and compared the results to measurements taken from non-athletes. They found that long-term cortisol exposure was indeed significantly higher in the athletes. Does this mean that endurance training is bad for our health, or at least bad in one particular way?

Enough is known about the many positive health effects of endurance training to say without qualification that, on balance, it is extremely beneficial to overall health. And since endurance training has been shown specifically to reduce abdominal fat storage, improve brain function and (except in cases of overtraining) enhance immune function, we can also say that high cortisol levels in endurance athletes do not have the same health implications that they have in non-athletes.

There can be too much of any good thing. Just as cortisol turns from good to bad when chronically produced in excess, endurance training turns from healthful to unhealthful when an athlete over-trains. In the over-trained athlete, high cortisol levels may have negative health effects, but even then high cortisol levels are just one of many imbalances seen in endurance athletes who work too hard and don’t rest enough.

As a runner, you don’t need to worry too much about cortisol. Just train smart and your hormones will take care of themselves.