Three hundred and fifty million people worldwide are affected by depression. In the United States, in 2013, estimates revealed that 6.7 percent of all American adults had suffered from a minimum of one major depressive episode during the past year. This was a total of 15.7 million adults. Estimates also show that around 17 percent of the American population will suffer at least one major depressive episode during their lifetime.

Physical health and depression can be interrelated.

The World Health Organization has stated that there are interrelationships at play between physical health and depression. One example of this is cardiovascular disease. The disease can lead to depression, just as depression may result in cardiovascular disease.

The WHO recommends that adults between 18 and 64 years old should engage in a minimum of 150 minutes per week of moderate physical activity. Alternatively, 75 minutes of vigorous physical activity can have the same effect, as can a mixture of both in the right quantities. WHO also recommends two or more days per week of muscle-strengthening activities involving major muscle groups.

Harvard Medical School reviewed medical studies that stretch back as far as 1981, and came to the conclusion that regular exercise can improve the mood of people suffering from mild to moderate depression. Exercise also can play a supportive role in treating those with severe depression. Additionally, studies have shown that those who take part in aerobic fitness programs enjoy both short- and long-term psychological benefits.

A 2004 research study concluded that exercise often is overlooked as an intervention by mainstream services in mental health care. Evidence has shown that exercise reduces depression, negative mood and anxiety. It also improves cognitive functioning and self-esteem. The WHO recognizes that depression may be prevented in the elderly by the use of exercise programs.

The biology of depression

As time goes on, we are understanding more and more about the biology of depression. Although the term chemical imbalance is a popular way to explain what causes depression, it really doesn’t go far enough to capture the complexity of depression. There are many possible causes, which can include genetics, brain chemistry that results in faulty mood regulation, medical issues, stressful life events and medications. The consensus is that a variety of these forces interplay to trigger depression.

Genetics and depression

In 2011 a European study found clear evidence that a region called 3p25-26, which is located on chromosome 3, can be linked to recurrent severe depression. However in this area of psychiatric genetics, numerous other studies have been carried out, and findings are not always consistently replicated. Yet the field is growing rapidly and technological advances will enable larger-scale studies to be carried out.

As important as this field is, it’s vital to remember that any genetical information that is discovered as part of medical studies, or on an individual patient basis, only provides one aspect of a patient’s personal history.

Outside and inside factors make up the whole

Well-being and mental pathology are influenced by the whole sum of the outside, as well as inside factors. The main inside factors are our complex brain chemistry, genetics and the nutrition our bodies receive from food, which comes originally from the outside. Outside factors, especially in the 21st century, are numerous. However, those which are known to trigger depression are stressful life events, medications and medical issues.

The easier outside factors that we can control, which studies have shown can prevent or help depression, are nutrition and exercise. Other outside factors, such as reactions to stressful life events, can also be helped with various therapies. A regular exercise program can trigger different brain chemistry.

Exercise and brain chemistry

Areas of the brain help to regulate our moods. A combination of specific brain chemicals, nerve cell and connections growth, along with how our nerve circuits function have a huge impact on depression. Experts believe that the production of new nerve cells (neurons) can be suppressed by stress. Neurotransmitters play an important part of this complex machinery. They relay messages between neurons, playing a vital role in how our nerve cells communicate with each other.

Exercise affects brain chemistry through a variety of mechanisms, which include neurogenesis, neurotransmitter release, and endorphin release.

Exercise and neurogenesis

Neurogenesis is the process of new neurons being created. FNDC5 is a protein that is released into our bloodstream when we are sweating. Over time this protein stimulates another protein, called BDNF – brain-derived neurotrophic factor — to be produced. This then triggers the growth of new synapses and nerves, while preserving existing brain cells.

This is especially exciting for those who are struggling with depression. It is also relevant for those over 30 years old, the age at which people begin to lose nerve tissue.

Neurotransmitters released during exercise

Exercise also stimulates the sympathetic nervous system, which then triggers more neurotransmitters. On top of this, serotonin and BDNF have a reciprocal relationship, each boosting the other. Serotonin, dopamine and norepinephrine are the neurotransmitters which are known to be released during exercise.

Serotonin helps regulate our moods, appetites, sleep patterns and inhibits pain. There has been plenty of research that shows some depressed people have lower serotonin transmissions. Serotonin causes feelings of happiness and security.

Dopamine is central to movement. It is also vital in how we perceive reality and in how motivated we are. It is also part of the brain’s reward system.

Norepinephrine is responsible for constricting our blood vessels and raising blood pressure. It is also thought to be linked to certain types of depression and can trigger anxiety.

Endorphin release

Endorphins are neuromodulatory chemicals, which means that they modify the actions of how our nerve cells respond to our neurotransmitters. They are released in response to stress and pain, and also to help alleviate depression and anxiety. Endorphins spark a more intense reaction than serotonin, that could be as extreme as ecstasy and euphoria, depending on the quantity of endorphins that are circulating.

Added benefits of exercise

Each of us has different amounts of neurotransmitters and endorphins in circulation. These are strongly affected by both nutrition and physical activity. Additionally, exercise reduces immune system chemicals that can exacerbate depression.

Along with the physical and psychological effects of exercise, a structured exercise program helps those with depression by giving purpose and structure to the day. Exercising outdoors comes with the added advantage of being exposed to sunlight, which affects our pineal glands, boosting our moods.

Planning an exercise program

If you or someone you know is suffering from depression, it is important to plan an exercise program that will work. Make sure the forms of exercise are enjoyable, and factor in more than one, if possible, as variety is the spice of life. Set some achievable goals and decide if you prefer to exercise in a group situation, by yourself or with an exercise partner. Many people find it helps to have a partner or group as part of their plan, to get support and to continue to feel motivated. Exercise logs can also be helpful, as a way of monitoring your progress.