It's common knowledge that stress can lead to a heart attack, but scientists have never actually known how—until now. It turns out that when you're stressed, your body starts overproducing white blood cells, or leukocytes, as if you had a wound or infection, researchers from the Harvard Medical School reveal in a study published yesterday. Those excess cells can then crowd artery walls, restricting blood flow and making a deadly clot more likely, the AFP explains. "It makes sense that stress wakes up these immune cells because an enlarged production of leukocytes prepares you for danger, such as in a fight, where you might be injured," co-author Matthias Nahrendorf tells Science.
The team began by taking blood samples from medical residents both while they were working in intensive care and while they were off-duty, and discovered that the stressed-out residents had higher white blood cell counts. They then verified the link to heart disease via experiments in mice. If that weren't enough to convince you to chill out, recent research has also shown a link between stress and memory loss, CNN reports. While acute stress (say, from a car accident) can sharpen your mental faculties and preserve a traumatic memory, low-level anxiety (like on-going job stress) harmed subjects' synapses. (This state was recently deemed America's most-stressed.)