Yahoo – AFP,
22 June 2014
Paris (AFP) - Scientists said Sunday they may have unravelled how chronic stress leads to heart attack and stroke: triggering overproduction of disease-fighting white blood cells which can be harmful in excess.
A nurse measures the blood pressure of a patient, on September 20, 2013 in Lens (AFP Photo/Philippe Huguen) |
Paris (AFP) - Scientists said Sunday they may have unravelled how chronic stress leads to heart attack and stroke: triggering overproduction of disease-fighting white blood cells which can be harmful in excess.
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.
White blood
cells "are important to fight infection and healing, but if you have too
many of them, or they are in the wrong place, they can be harmful," said
study co-author Matthias Nahrendorf of the Harvard Medical School in Boston.
Doctors
have long known that chronic stress leads to cardiovascular disease, but have
not understood the mechanism.
To find the
link, Nahrendorf and a 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.
Particularly,
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 buildup.
The study
then moved on to mice, which 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.
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