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This question originally appeared on Quora. Answer by James Porter.

Sudden cardiac death often comes with no warning signs what so ever.

Of all the diseases and disorders that can be caused or made worse by stress, the relationship between stress and heart disease, is probably the most clear. In a study of 12,000 Danish nurses, conducted over 15 years, those nurses who reported high levels of stress had a 50% increase in heart disease.

In another study that compared College professors and teachers to Physicians, Lawyers, Real Estate and Insurance Agents, the professionals in second group died of heart disease at twice the rate of the professionals in first group. This study, reported on in a “Total Worker Health” webinar on the National Institute for Occupational Safety and Health (NIOSH) website, allowed (controlled) for differences in exercise, diet and smoking between the two groups so the authors concluded the main reason for this difference in death rates was job stress.

There’s a doctor who works at Brigham and Women’s Hospital in Boston named Martin Samuels who studies the relationship between THINKING and heart disease. He actually collects medically verified cases where perfectly healthy people have literally been scared to death. In this article from Scientific American you can read for yourself how a healthy person can suddenly die from too much stress.

The article explains that the fight or flight response, (aka, the stress response) first studied by Harvard researcher, Dr. Walter B. Cannon, causes a reaction in the body that dumps adrenaline and cortisol into the blood stream. These stress hormones help to rev up our bodies (and the heart in particular) to prepare us to fight an attacker or flee to safety. This high octane response worked great for our prehistoric ancestors. But in our relatively safe modern world, this same response can prove deadly.

Nowadays we activate this response to PERCEIVED threats (like when your boss criticizes your work). And thus we find ourselves in situations where we can’t fight and we can’t flee, with all these stress hormones racing around our bodies. Sometimes (and it’s rare) this response is so overwhelming, and so much adrenaline and cortisol are dumped into the blood stream that it can bring on sudden cardiac death.

Before he died, in the 1940’s,Walter B. Cannon himself published an article in a medical journal about verified examples of “voodoo death.” What he realized back then was the powerful effect stress had on the body. So powerful in fact, that someone who believed that they were going to die, would die, just by being scared to death. And that turned out to be true.

Let me assure that the chances of dying in the ways I’ve described above are remote. However, research shows that chronic stress (that’s when your stress goes on for months and months without let up) can lead to inflammation which can lead to hardening of the arteries (or arteriosclerosis) which can lead to heart disease. Inflammation is regulated by our immune system, and that system is very sensitive to stress.

Mostly our immune system protects us from harm. For example, when you cut yourself, the immune system responds by sending special warrior cells to the site of the cut to fight off infection. That’s a good thing. But when this same process occurs inside our bodies, particularly in blood vessels, (or against healthy, non-invasive cells) that process can gradually lead to heart disease and stroke and all kinds of other stress-related health problems (like auto-immune disorders).

The bottom line is stress can kill you quickly or it can kill you slowly. Take your pick. By causing you to dump massive amounts of stress hormones into the blood stream it can bring on sudden cardiac death. By causing you to have slightly elevated levels of these same hormones over longer periods it can bring on inflammation first, and heart disease later.

I write a blog about stress at my website www.StressStop.com. I’ve also written a book entitled STOP STRESS THIS MINUTE.

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