New Research Shows Why Chronic Stress Leads to Heart Attack

Amy Taylor June 26, 2014

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Scientists may have figured out why chronic stress leads to heart attack. In a new study, a group of researchers from Harvard Medical School in Boston found that stress triggers overproduction of disease-fighting white blood cells which can be harmful in excess.

Doctors have long known that chronic stress leads to cardiovascular disease, but have not understood the mechanism. Surplus cells clump together on the inner walls of arteries, restricting blood flow and encouraging the formation of clots that block circulation or break off and travel to another part of the body.

To find out possible explanation for the link, Matthias Nahrendorf and his team studied 29 medical residents working in an intensive care unit.

Their work environment is considered a model for chronic stress exposure given the fast pace and heavy responsibility they carry for life-and-death decisions.

Comparing blood samples taken during work hours and off duty, as well as the results of stress perception questionnaires, the researchers found a link between stress and the immune system.

They noticed stress activate bone marrow stem cells, which in turn triggered overproduction of white blood cells, also called leukocytes.

White blood cells, crucial in wound healing and fighting off infection, can turn against their host, with devastating consequences for people with diseases like atherosclerosis—a thickening of artery walls caused by a plaque build-up.

The researcher conducted the same experiment on mice. Subjects were exposed to the rodent equivalent of stress through techniques like crowding and cage tilting.

The team chose atherosclerosis-prone mice.

They found that excess white blood cells produced as a result of stress accumulated on the inside of arteries and boosted plaque growth.

"Here, they (the cells) release enzymes that soften the connective tissue and lead to disruption of the plaque," said Nahrendorf.

"This is the typical cause of myocardial infarction (heart attack) and stroke."

He added leukocytes were only a part of the picture—factors like high cholesterol and blood pressure, smoking and genetic traits also contribute to heart attack and stroke risk.

"Stress might push these over the brink," the researcher told AFP.

Source of this article:

Chronic variable stress activates hematopoietic stem cells, Nature Medicine