You probably already know that stress takes a toll on just about every part of our body, from our cardiovascular and respiratory function to our sex drive and menstrual cycle, according to the American Psychological Association. It can even lower our immunity so we’re more likely to get sick. But an English study has just revealed yet another negative effect of chronic stress: It’s expanding our waistlines.
To determine the relationship between chronic stress and weight, researchers from the University College London in the U.K. took hair samples from 2,527 men and women and measured their amounts of cortisol (the notorious stress hormone). The hair of those who had BMIs of 30 or greater—which is considered obese, had higher concentrations of cortisol.
Cortisol, which is produced in our adrenal glands, is the primary stress hormone that sounds alarms in the parts of our brain that control fear, motivation, and mood. It also pumps glucose into the bloodstream so we have the resources we need to manage those threats. Normally when a perceived threat has passed, our body reverts to its normal functioning, but in the case of chronic stress, our system’s defense mechanism stay on perpetually—leading to consistently high levels of cortisol. “It’s providing glucose to the brain, keeping things going during a stressful event,” study author Sarah E. Jackson, PhD, has said. “It also plays a huge role in metabolism, body composition, and the accumulation of body fat.”
Bad news for people with a high-stress lifestyle: Sky-high levels of cortisol were linked not only with higher BMIs, but also with larger total waist circumference. That’s especially unhealthy, as past studies have highlighted a link between abdominal adiposity (stored belly fat) and increased risk for coronary disease and type 2 diabetes.
As you might expect, cortisol levels were lowest in the hair samples of slimmer participants and highest in those who were obese. The researchers used hair samples instead of blood or urine to get a more accurate read, as blood and urine samples show only our current status and don’t provide longer term information. The researchers clipped two centimeters of hair from each participant, which is about two months of growth, which opens a window into levels of cortisol over that period of time, according to Jackson.
Though the findings strongly suggest that people with chronic stress are at a higher risk of becoming and staying obese, Dr. Jackson cautions that since it was not a longitudinal study, more research is needed to determine cause and effect. She says the team will “continue to weigh and measure our study participants every four years to determine the ways stress affects body mass over time.”