Missing link between stress and heart attacks discovered
It has long been known that sustained stress can cause fatal heart attacks and strokes, but scientists have never understood exactly why.
Now research has suggested an answer.
It was known that stress triggers the "fight or flight" mechanism, sending a surge of adrenaline to help the heart pump harder and increase blood flow.
This enables the body to fight or run when encountering a perceived threat.
But the new study has suggested that stress also sends the immune system into overdrive, increasing white blood cells and worsening inflammation in the arteries. This can cause huge problems if arteries are already thickened with plaque.
When damaged arteries become more inflamed they produce lesions which can break away, leaving an open wound that blood platelets and clotting proteins rush to fill.
A clot can enlarge in moments, and if it completely obstructs the artery it will cause a heart attack.
Dr Matthias Nahrendorf and his team at Massachusetts General Hospital and Harvard Medical School discovered that junior doctors who were regularly exposed to chronic stress had very high white blood cell counts.
They also found that when mice were stressed, the stem cells in their bone marrow were activated and produced large numbers of white blood cells, leukocytes.
Where mice already had thickened arteries, atherosclerosis, the blood cells increased inflammation and caused the same lesion-like plaques to form that can rupture in humans and cause heart attacks.
"Exposure to psychosocial stress is a risk factor for many diseases," said Dr Nahrendorf.
"To explore the impact of stress on the human immune system, we analysed blood samples from 29 medical residents working on a hospital intensive care unit, a challenging, fast-paced work environment that frequently includes the life-or-death decisions.
"Compared to when off duty, residents working on the ICU reported an increased stress perception. When comparing samples taken during work to samples taken off duty, we observed an increase in white blood cells.
"When atherosclerosis-prone mice were subjected to chronic stress, accelerated (blood cell production) promoted plaque features associated with vulnerable lesions that cause heart attacks and strokes in humans," the report said.
The team found that an "inhibitor" drug that stopped stem cells from producing white blood cells also prevented the build-up of plaque in the arteries, offering hope for new treatments. (© Daily Telegraph, London)