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Scientists have long known that stress complicates a host of health problems. Now they are discovering that chronic stress — a mainstay of modern life — doesn't merely exacerbate disease, it actually can cause it.
"We are just beginning to understand the ways that stress influences a wide range of diseases of aging, including heart disease, metabolic syndrome, type 2 diabetes and certain types of disability, even early death," says Sheldon Cohen, a professor of psychology at Carnegie Mellon University in Pittsburgh who has been at the forefront of stress research for 30 years.
Everyone experiences stress, of course, but it's particularly prevalent among adults over 50. In a recent Harvard University-Robert Wood Johnson Foundation-NPR poll, about a quarter of 2,500 participants said they'd experienced "a great deal" of stress in the last month. Another poll, conducted in August by AARP, found 37 percent of adults over 50 experienced a major stressful life event in the past year, such as the death of a family member, chronic illness or a job loss.
Certainly, many people who are stressed end up eating, drinking and smoking more, and sleeping and exercising less — tendencies that have obvious negative consequences for our health. But scientists are discovering a much more nuanced picture, says Bruce McEwen, a neuroscientist at Rockefeller University in New York and the author of The End of Stress as We Know It.
The human body reacts to stress by first pumping adrenaline and then cortisol into the bloodstream to focus the mind and body for immediate action — a response that has ensured our survival over the millennia. The adrenaline rush from the initial stress response can occasionally pose health risks, according to Cohen, but the more significant hazard is the subsequent release of cortisol. Generally considered a bad stress hormone, cortisol does serve many important functions — one of which is turning off inflammation. But when chronic stress exposes the body to a relentless stream of cortisol, as happens when stress is constant, cells become desensitized to the hormone, "causing inflammation to go wild," Cohen says. Long-term chronic inflammation damages blood vessels and brain cells, leads to insulin resistance (a precursor to diabetes) and promotes painful joint diseases.
Here are eight other conditions that may be caused by stress.
1. The common cold
In one groundbreaking 2012 study, Cohen and his colleagues interviewed 276 healthy adults about stressful events in their lives and then exposed them to a cold virus. Those experiencing chronic stress were cortisol resistant — and were more likely to get sick. "The immune system's ability to regulate inflammation predicts who will develop a cold, but more importantly it provides an explanation of how stress can promote disease," Cohen says. "When under continuous stress, cells of the immune system are unable to respond properly, and consequently produce levels of inflammation that lead to disease."
2. Weight gain
We've long known that stress hormones stimulate a preference for foods that are full of sugar, starch and fat — that's why we're more likely to reach for a candy bar to get through a stressful day at the office. But new research shows that the link between stress and weight gain is far more complex than simply poor food choices. In a study published in July in Biological Psychiatry, women who had one or more stressful events during the previous 24 hours burned 104 fewer calories in the seven hours following a fast-food meal than women who ate a similar meal but were stress-free. Although 104 calories may sound negligible, that can add up to 11 extra pounds a year. In addition to triggering these apparent changes in metabolism, the stress response produces a rise in insulin levels and a fall in fat oxidation, a dual process that promotes fat storage, says stress researcher Janice Kiecolt-Glaser, professor of psychiatry at Ohio State University College of Medicine in Columbus and the study's lead author. Other research has revealed a correlation between excess cortisol and abdominal fat.
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