Uncovering why stress is a killer

It has long been known that sustained stress can cause heart attacks and strokes, but scientists have never understood exactly why.

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. A 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 that 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, stem cells were activated and produced large numbers of white blood cells.

The team found an "inhibitor" drug that stopped stem cells from producing white blood cells prevented the build-up of plaque in the arteries, offering hope for new treatments.

The findings were published in the journal Nature Medicine.