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Dr. Schlundt, Health Psychology
Part One: What Is Depression??
To understand how exercise treats depression, it is necessary to first understand what depression is. We all feel the blues from time to time. The word depression is commonly used in everyday conversation to indicate a momentary feeling, sometimes due to specific causes: “You seem very depressed today” or “She’s depressed about her test”, for example.
depression refers to a long, drawn-out period of constant despair. It can often
be difficult to define depression in concrete terms. One can get a general
approximation of what depression is by looking at a list of symptoms. On its website,
I am sad more days than not
I feel hopeless about the future or pessimistic most of the time.
I feel guilty about things I have done or not done.
I have thought about hurting or killing myself.
Historically, depression as well as other mental illnesses have been viewed with suspicion. Patients may be told to “just snap out of it”. However, depression is not simply a character trait. It may be caused by so-called “external events”. In fact, there are two types of depression, primary and secondary; primary depression has no obvious cause while secondary depression is caused by outside events. Nevertheless, both types are associated with real physiological effects in the brain—in particular, with low levels in the brain of a neurotransmitter called serotonin .
are chemicals in the brain that act as signals, and serotonin is a
neurotransmitter that transmits “messages across nerve cells in the
brain”, according to Dr. Patrick J. Bird from the
The exact nature of the link between depression and serotonin remains unclear (Mark, 2003): it has itself been the subject of many studies and experiments. Depression does not necessarily result from low serotonin levels; however, it is has been established that the brains of depressed people do have lower serotonin levels, and that depression can be treated through drugs that elevate serotonin levels.
Part 2: The Rationale
So how exactly does exercise treat depression? There are two explanations for this: the biological explanation and the psychological explanation.
The prevailing hypothesis is that exercise increases serotonin levels; the relationship between serotonin levels and depression has been well-established (as was pointed out before).
Exercise also stimulates the release of endorphins; this is commonly known as “the runner’s high”. Endorphins are the body’s own natural painkillers, working much like morphine does—in fact, morphine attaches to the same brain receptors that morphine does. However, endorphine always stays in the bloodstream and has no way of crossing over into the brain—which is why many scientists believe that endorphine release has little to do with depression (Frayne, 2002).
Production of the chemical phenylethylamine during exercise is another possibility; British scientists have hypothesized that an enzyme converts the phenylethamine into phenylacetic acid, which (unlike endorphins) can cross over to the brain (Why exercise cheers you up, 2001). It has been established that depressed patients have very low levels of both that enzyme and of phenylethamine itself. However, results are not entirely conclusive and further research needs to be done.
An alternate rationale as to why exercise improves mood is entirely psychological. Critics of the biological explanation point out that exercise does, after all, offer psychological benefits that are completely unrelated to actual chemical changes in the brain:
a. The mastery hypothesis: the mere fact that they are exercising makes patients feel like they have achieved something, cheering them up much as learning a new hobby or achieving a certain goal might cheer them up.
b. The distraction hypothesis: exercising physically forces depressed patients to take their minds off of whatever external causes might be triggering their depression
c. The social interaction hypothesis: exercise is often done with other people, and the antidepressant effect of exercise can be attributed to the sense of well-being that comes from being socially connected.
Part 3: What claims are being made?
Dr. Joseph Mercola of the Total Health Program cited a British Journal of Sports Medicine article, claiming that “exercise [is] better than drugs for depression”. At the same, he pointed out that it was not a complete cure. He also cited a research study done at Duke (2006).
Possible bias into his claims might be introduced by the fact that Dr. Mercola is the author of the “Total Health Program”, a program that places emphasis on nontraditional treatment (through diet and exercise) over traditional medication. By claiming that exercise treats depression, he might be encouraging patients to buy his book and investigate other non-pharmaceutical treatments for other diseases.
Part 4: What scientific research is available?
A great deal of scientific research has been done on exercise as a way of treating depression. In one of the more relevant studies, Dimeo, Bauer, Varahram , Proest and Halter (2001) evaluated the short term effects of exercise on patients with mild to moderate depression. Twelve patients who had been officially diagnosed with at least one major episode of depression (on average, lasting thirty-five weeks) participated. The researchers had the patients walk on a treadmill 30 minutes a day for 10 days. The level of depression was measured by self-assessment on the Hamilton Scale. By the end of ten days, participants rated their participation scores as being significantly less—on average, there was a drop from 19.5 to 13, and a drop in intensity of symptoms from 23.2 to 17.7. It was concluded that aerobic exercise was in fact effective for reducing symptoms of depression.
The side effects involved with this type of treatment are minimal, beyond the general effects of possible overexercising: joint pain, aches, exhaustion. If it is assumed that the effect of exercise on depression is based on a psychological mechanism, then there could be some danger. For example, if the depressed patient begins to tie his or her self-worth to the sense of accomplishment achieved through exercise, then once treatment is stopped there might be a relapse. I wondered if using physical fitness as a way to boost self-confidence might not eventually lead to eating disorders, but I could find nothing to support this idea.
In fact, it appears that for the most part the only controversy is over the specific mechanisms (whether psychological or biological) through which exercise treats depression, and not over the question of whether exercise treats depression in the first place.
Bird, Patrick J. Exercise Addiction. (1999). Retrieved September 19, 2006 from
Dimeo, F., Bauer & Varahram & Proest & Halter. (2001). Benefits from aerobic
exercise in patients with major depression: a pilot study. The British Journal of
Sports Medicine xxxv, 114-117. Retrieved September 18, 2006 from
Retrieved September 20, 2006 from http://serendip.brynmawr.edu/biology/b103/f02/web1/sfrayne.html
How Does Exercise Affect Mood? (2003). Retrieved September 19, 2006 from
Johnson, CJ. Serotonin: A powerful neurotransmitter. Retrieved September 17, 2006
Mercola, Dr. Joseph R. (2006?). Exercise better than drugs at relieving depression.
Retrieved September 17, 2006 from http://www.mercola.com/2000/oct/15/exercise_depression.htm
Moran, Mark. Depression-Serotonin Link: Many Mysteries Remain. (2003) Retrieved
September 19, 2006 from http://pn.psychiatryonline.org/cgi/content/full/38/9/48
Why exercise cheers you up. (2001). Retrieved September 19, 2006 from
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