exercise and depression

Exercise And Depression: Slimming down the body while fattening up the brain

There is evidence that vigorous exercise is good for one's health and can, if not too stressful, improve the immune system. It can also reduce the chances of heart disease and increase lifespan. But is that why we all do it? I recently went round asking my running friends. One did it in order to be alone, one to be healthy, but most said that they ran in order to avoid feeling 'low', or slightly depressed.

The standard story is that vigorous exercise increases the levels of endorphins in the brain and this gives one a sense of well-being. I certainly find that jogging makes me deal much better with stress and I believe my physical activity staves off depression. I do not think I could have survived the period when I was nursing my wife who was suffering from cancer without regular vigorous exercise.

Striking new evidence about cells
Though there is published work showing runners to be less depressed than the general population, the mechanism is far from clear. Now there is striking new evidence relating to the brain, depression and exercise. It has been found that contrary to the long-held view that no new neurones are generated in adults, it is now clear that there are stem cells in various regions of the adult brain that divide to give new neurones. Stem cells are special cells which have the remarkable property that, when they divide, one of the two daughter cells remains a stem cell and can divide again while the other cell can become a specialised cell like a nerve cell. The first suggestion for this came from birds in which new nerve cells were generated in relation to song-learning.

Then came studies of the brains of patients who had died of cancer and who had previously given permission to be treated with a substance that labels dividing cells. These showed the formation of new nerve cells - a revolutionary discovery which has completely changed the way disease of the brain can be thought about and it opens up possibilities for quite new therapies.

It is of particular relevance to depression.
The hippocampus is a region of the brain that is associated with memory, particularly the conversion of short-term memories into long-term memories, and is also involved in mood disorders. There is evidence that the hippocampus is smaller in the brains of depressed patients. In one study involving 10 depressed patients, the volume of the hippocampus was measured using magnetic resonance imaging, and was found to be about 10% smaller than those in controls of similar age, matched for height, education and even-handedness. Other studies support this finding.

Exercise multiplies brain cells
The reduction in the size of the hippocampus may be related to the effects of stress. Stress suffered over quite a long period due, for example to a significant loss, is a common trigger for depression. Stress causes an increase in certain hormones such as cortisol which can, in turn, cause both cell deterioration and cell death in the brain. The new research on generation of neurones has found that this occurs in the hippocampus. It also shows that stress can inhibit cell multiplication in the hippocampus in an animal model, resulting in fewer nerve cells being produced. Antidepressants like Prozac can, by contrast, promote an increase in cell proliferation and this offers a totally new perspective on how antidepressants may act: it seems likely, though the evidence is at an early stage, that antidepressants work by increasing brain cell growth.

Of particular significance is the effect of exercise. Mice which had access to a running wheel so that they ran nearly five kilometres a day for several months had twice as many multiplying cells in their brain compared to mice which took no exercise. I would like to believe that this is true in humans too, and that exercise can effectively act as a natural antidepressant. Certainly, that is my experience.

Above all, I like the idea of running keeping my body thin - and my hippocampus fat.

Lewis Wolpert

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