“We don’t know which came first, the greater body weight or the higher cortisol,” said researcher Andrew Steptoe. He’s the British Heart Foundation professor of psychology at University College London.
For the study, Steptoe’s team analyzed levels of cortisol in a lock of hair about three-quarters of an inch long, cut as close as possible to the scalp. This hair sample reflected accumulated cortisol levels over the previous two months, the researchers said.
Cortisol is the body’s primary stress hormone, triggered when you have a “flight-or-fight” response to danger. It benefits you to escape danger, but if cortisol levels stay chronically high, it is linked to depression, weight gain, anxiety and other problems, according the Mayo Clinic.
The study included more than 2,500 adults in England, aged 54 and older.
The researchers compared cortisol levels in the sample to body weight, waist circumference and body mass index (or BMI, a rough measure of body fat based on height and weight measurements). They also looked at how cortisol levels related to persistent obesity.
Those participants with higher cortisol levels tended to have larger waist circumferences (over 40 inches for men, over 35 inches for women and a risk factor for heart disease and other problems). People with higher cortisol levels also had higher BMIs — the higher the BMI, the higher the levels of body fat.
Higher cortisol levels were also tied to greater obesity levels that persisted over the four years examined.
Although the study found an association between cortisol and obesity, it did not prove a cause-and-effect link.
One U.S. expert also questioned the method used in the study. Currently, “the evidence for using hair samples as a weight or obesity predictor is lacking,” said Connie Diekman. She’s director of university nutrition at Washington University in St. Louis.