By using hair to measure long-term levels of the stress hormone cortisol, British researchers confirm a link between chronic stress and weight gain, as well as with the difficulty of combating excess weight.
Previous research had shown that high levels of cortisol in the blood, urine, or saliva were associated with obesity. However, these measurements can vary depending on factors such as the time of day and do not account for long-term stress levels, the study team notes in the Journal of Obesity.
"When people are faced with a stressful situation, a chain reaction is triggered in the body, resulting in the release of cortisol, which leads to higher levels of this hormone in the body," said study lead author Sarah Jackson of University College London. "Cortisol is involved in a wide variety of biological processes, including metabolism, body composition, and body fat accumulation," she said. "When we are stressed, we may also have more difficulty finding the motivation to go for a run or resist unhealthy foods."
How stress works?
Stress triggers alarms in the brain that signal the nervous system to release hormones to sharpen the senses, tense the muscles, speed up the heart rate, and breathe more deeply. Commonly called "fight or flight," this biological response helps us defend ourselves in threatening situations. Isolated or temporary stressful situations may be harmless, but regular exposure to stress can lead to problems with the immune system, heart disease, complications of the nervous system, mental health disorders, and obesity.
About the study
For the study, researchers examined data collected from men and women aged 54 and older participating in the English Longitudinal Study of Ageing. Since 2002, participants have undergone tests every two years, and during the sixth wave of the study, they provided a hair sample.
The study team tested cortisol levels that accumulated in the hair over time in 2527 men and women, and found that participants with more cortisol in their hair were also more likely to be obese or have excess abdominal fat. Researchers examined cortisol levels in the two centimeters of hair closest to the scalp, which typically represents about two months of growth. They also examined weight, waist circumference, and body mass index (BMI), a measure of weight relative to height.
The study showed that participants considered obese based on their BMI or waist size had particularly high levels of hair cortisol. By analyzing weight and body fat data from assessments conducted over the four years prior to hair sampling, researchers also found that obesity tended to persist over time for people with the highest cortisol levels.
The study was not a controlled experiment designed to prove how stress directly affects cortisol levels or weight gain. Among other limitations, the authors mention the typology of the studied population mainly consisting of white and relatively older adults, which means that the results may be different in a younger population and composed of more diverse ethnic groups.
Stress and overweight, going further
"Even so, the results add to the growing body of evidence linking stress to obesity," said Dr. Susan Fried of the Icahn School of Medicine at Mount Sinai in New York. However, considering the study's results, no real solution is given to allow people to eliminate excess weight. "I don't think there's strong evidence or uniform studies indicating that reducing stress itself causes weight loss," said Fried. "There is a body of evidence indicating that sleep is very important; people overeat when they haven't rested enough."
The results suggest that people may need to consider a holistic approach to weight loss that goes beyond diet and exercise, to consider factors such as stress, said Dr. David Katz, director of the Yale University Prevention Research Center in New Haven, Connecticut. "You might think you need to improve your diet, or exercise more, and that's true," said David Katz, who was not involved in the study. "But for you, the top priority might be better stress management so you're more likely to do those things, and to reduce the hormonal response that obstructs weight control."
Sources: Reuters Health, Fri Mar 31, 2017, Lisa Rapaport, journalist. References: Hair cortisol and adiposity in a population-based sample of 2,527 men and women aged 54 to 87 years. Sarah E. Jackson, Clemens Kirschbaum, Andrew Steptoe.