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Stress is misunderstood and not always bad; it is the way our body has evolved to deal with life’s challenges. Unfortunately our physiology is stuck in the days when we were running across the African savannah chasing or being chased by predators and has not kept up with the world we live in now. Our stress response use to be life saving and kick into the “FLIGHT or FIGHT” response, to run away or fight that marauding lion in Africa. Usually our stressors are not that extreme these days – traffic jams, money worries, overwork – few of them are ‘real’ in that they are not immediately ‘life threatening’ in the sense of running away from the lion; but our response is often the same and can cause a lot of health problems.

Hormones and Stress

Hormones released by the brain (luteinizing and follicle stimulating hormones) stimulate sperm production. With stress this system is inhibited, the levels of these hormones decrease, the testes take a nap and the result is a decline in circulating testosterone levels and quality of sperm. The stressor can be injury, illness, starvation, exercise or psychological. Testosterone levels plunge at the onset of a stressor for a number of reasons. Endorphins and enkephalins (mostly the former) act to block the release of luteinizing hormone and follicle stimulating hormones. Also higher levels of glucocorticoids* are circulating which again are blocking the response of the testes to the sperm stimulating hormones.

Exercise and Stress

Exercise is good for you but at some point too much can damage various physiological systems. There are optimal points of balance. Men who do extreme amounts of exercise running more than 40 to 50 miles a week have lower amounts of luteinizing hormone and testosterone circulating. This is due to the role of endorphins and helps account for the “runners high”. Not every man’s reproduction will be impacted. But if you have poor quality sperm and exercise a lot, this might be an area of your life you might want to re-evaluate.

 Our bodies are not designed to be sympathetically dominant all the time, especially without a chance to burn the released adrenaline. It needs to be at rest after activation; calmness after a storm. Chronic stress does not allow for the calm.

If you want a more detailed biological explanation of the mechanism of stress on the body and related disease (it’s both fascinating and scary!) and where much of this information in this article has been sourced, I’d recommend reading Robert Sapolsky’s Why Zebra’s Don’t Get Ulcers.


*Glucocorticoids: A hormone that predominantly affects the metabolism of carbohydrates and, to a lesser extent, fats and proteins (and has other effects). Glucocorticoids are made in the adrenal gland and chemically classed as steroids. Cortisol is the major natural glucocorticoid.