Sustained or chronic stress leads to elevated hormones such as cortisol, the “stress hormone,” and reduced serotonin and dopamine production which have been linked to depression. These chemical systems regulate biological processes like sleep, appetite, energy, and sex drive, and permit expression of normal moods and emotions and when they are out of balance everything is else out of whack as in the case when someone develops depression.
Exercise has been shown to be effective at treating and preventing depression. In 1999, a randomized controlled trial showed that depressed adults who took part in aerobic exercise improved as much as those treated with Zoloft. A 2006 meta-analysis of 11 studies bolstered those findings and recommended that physicians counsel their depressed patients to try it. A 2011 study took this conclusion even further: It looked at 127 depressed people who hadn’t experienced relief from SSRIs, a common type of antidepressant, and found that exercise led 30 percent of them into remission—a result that was as good as, or better than, drugs alone.” But how exactly does exercise help combat depression and how much exercise is necessary to have a positive effect?
The brain is a very complex organ, depression has multiple causes and involves multiple systems. Research still isn’t clear about exactly how exercise combats depression but the main hypothesis is that exercise combats depression by enhancing endorphins which are natural chemicals that act like morphine and other painkillers. Endorphins reduce or block the spread of messages related to pain, stress and emotional distress between the body and the brain. They have been called the body’s “natural painkillers.”
Research into the link between endorphins and depression is still new but one study by Jon-Kar Zubieta, M.D., Ph.D., found that women who were suffering from depression showed a greater response in their mu-opiod system in response to recalling a stressful life event compared to women who were not depressed. The mu-opiod system is the system in the brain that regulates pain and responds to endorphins and painkillers like morphine. In this situation recollection of the stressful event produced a greater emotional response associated with pain in women who were suffering from depression. This study indicates that people who suffer from depression have an overactive mu-opiod system.
It makes sense that since exercise raises the natural level of endorphins in the brain and there is a link between the mu-opiod system and depression that regular exercise would have a positive/mitigating effect on depression.
There’s also a theory that aerobic activity boosts norepinephrine, a neurotransmitter that plays a role in mood. A lot of the new antidepressant drugs are selective seratonin/norepinephrine reuptake inhibitors which increase levels of serotonin and norepineprine in the brain. Also like antidepressants, exercise helps the brain grow new neurons.
Elevating endorphins and norepinephrine aren’t the only ways that exercise helps the body combat stress induced depression. A recent study published in the Journal Cell points to evidence that exercise may be helping our brains by making our bodies more efficient at removing harmful chemicals that are triggered by stress.
Researchers from the Karolinska Institute in Sweden wanted to discover how well-trained skeletal muscles may provide the brain with an edge over stress, and ultimately engender protection against stress-related depression. It was discovered that a certain protein called PGC-1a1 that is present in higher levels in well-trained muscle tissue has a protective effect against depression.
In this study mice were bred or genetically modified to have higher levels of PGC-1a1. This was the experimental group. The control group consisted of regular non-genetically modified mice. Both groups were subjected to stress in the form of aversive stimuli such as flashing lights, loud noises and interrupted sleep for 5 weeks. After the 5 weeks the control group exhibited symptoms of depression but the experimental group with higher PGC-1a1 levels showed no symptoms of depression whatsoever.
The researchers also found that in addition to higher levels of the protein in their blood, the genetically-modified mice also had higher levels of KAT enzymes that convert a stress chemical called kynurenine into a form more easily metabolized by the body. What these results suggest is that well-trained muscles aren’t just stronger and faster — they also catalyze chemical reactions that help our bodies metabolize byproducts of stress. In this way well-trained muscles function similarly to the kidneys and liver in helping the body get rid of harmful substances.
How much exercise and what kind of exercise is necessary to confer all these protective benefits against depression that these studies talk about? Based on research, aerobic exercise is the most effective form of exercise for people with major depression but there is also research which supports resistance training.
Research suggest that people should participate in three to five exercise sessions per week that are 45 to 60 minutes in duration. These exercise sessions should combine aerobic and resistance training forms of exercise. For aerobic exercise the recommended intensity is 50 to 85 percent of a person’s maximum heart rate. For resistance training a combination of upper and lower body exercises is recommended with three sets of eight repetitions at 80 percent of the maximum weight that the person can lift at one time.
Findings suggest that people may experience a relief in depression in as little as four weeks after starting an exercise program. However the exercise regimen should be continued for at least 10 to 12 weeks to achieve the greatest antidepressant effect.
Putting it all together, prolonged stress –whether life or work related– can cause depression. Regular aerobic and resistance exercise buffers stress and combats depression through a number of different mechanisms. A qualified health and fitness professional can put together the most effective exercise program for you to achieve a maximum antidepressant effect, help you stay on track until favorable results are achieved, and help maintain you at an optimal level of physical and mental health.