This article originally appeared on Health.com.
Sure, your life is bananas. And maybe you feel like you can manage it all just fine. But here is a powerful reason to pencil in some me time: Feeling stressed for months at a time can up your risk for obesity, according to scientists from University College London.
Their new study used hair clippings to measure levels of the stress hormone cortisol in people’s bodies. Hair samples provide more accurate hormonal data than other types of samples, the authors say, making their findings some of the strongest yet to suggest that stress and weight are closely linked.
For the study, published today in Obesity, the researchers collected locks from more than 2,500 men and women over a four-year period, and analyzed them for accumulated levels of cortisol. (The samples were cut as close as possible to the scalp, and represented hair growth over about two months.)
The researchers also recorded participants’ weight, body mass index (BMI), and waist circumference over time. And they noticed a clear connection: People who had higher levels of cortisol in their hair tended to rank higher on all three physical measures, as well.
In fact, people classified as obese based on their BMI (30 or greater) or waist circumference (greater than 102 centimeters in men or 88 centimeters in women) had particularly high levels of cortisol in their hair.
These findings support previous research that suggest that high stress levels can trigger unhealthy habits—like losing sleep and eating “comfort food” high in sugar and fat. Other studies have shown that cortisol levels can affect metabolism and fat storage in the body, implying that weight gain could potentially occur even if a person’s behaviors don’t change.
But most studies have relied on measurements of cortisol in blood, saliva, or urine—which can vary depending on situational factors and time of day. The relatively new technology of measuring hair cortisol provides more accuracy for long-term cortisol measures, say the authors, and strengthens the existing research.
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The association between cortisol levels and waist circumference is particularly important, says lead author Sarah Jackson, PhD, a research psychologist in the department of Behavioral Science and Health, since carrying fat around the midsection is a known risk factor for heart disease, diabetes, and early death.
The authors noted that their study participants were all 54 and older and mostly white, and pointed out that the study’s findings may not apply to a younger or more diverse group of people. They also can’t say which came first: obesity or elevated cortisol levels.
Susan K. Fried, PhD, professor of medicine, endocrinology, diabetes, and bone disease at Icahn School of Medicine at Mount Sinai, said in an email that it’s possible that obesity could trigger higher stress levels. The study’s cortisol measurements reflect exposure over a couple of months, “but the obesity in the people studied likely developed many years earlier,” says Fried, who reviewed the research but was not involved herself.
“Thus, these high hair cortisol values may simply reflect social or biological stress associated with being obese,” she says. For example, stigma and medical conditions associated with being overweight (such as high blood pressure and arthritis) could both cause stress over time.
Jackson agrees that this is a possibility, but says it can’t hurt to be aware of how stress might influence weight gain: “I think the take-home message from our study is really to try and maintain awareness of healthy lifestyle habits during times of stress.”
“When we’re stressed out we may find it more difficult to find the motivation to go for a run or resist unhealthy foods, and that’s when it is easier for weight to creep on,” she says. It could also be helpful to identify ways to reduce exposure to stressful situations, she adds, or to find ways of coping with stress that don’t involve food.
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If further research is able to identify a cause-and-effect relationship—that is, show that stress and cortisol levels are directly responsible for fueling weight gain—it could lead to new ways of using stress reduction to prevent and treat obesity, says Jackson.