Long-term stress leads to higher obesity risk

Feeling stressed in the midst of midterm season, you may find it particularly hard to resist the mouth-watering bag of chips or chocolate bar lying quietly next to your desk. Just one bite, the brain thinks as the hand reaches out. After the first bite, all the cells in your mouth light up in joy. Without realizing, the snack disappears in a blink of an eye.

According to a recent study, published in the journal Obesity, a group of researchers associated long-term exposure to high levels of cortisol, the stress hormone, with obesity. This research involved over 2000 men and women in England at least 50 years old and lasted for over four years.

The World Health Organization (WHO) states that obesity has doubled worldwide since 1980 and the majority of the world population lives in countries where being overweight or obese leads to more deaths than being underweight does.

There have been several studies conducted in search of the link between obesity and cortisol. However, the majority of those studies relied on measurements taken from the saliva or urine. Although these assessments can accurately determine cortisol levels at specific times, they do not capture cortisol concentrations over long periods of time.

Due to this disadvantage, many studies have yielded conflicting results. Some studies reported that stressed people tend to eat more, while others say that people eat less under acute stress. Recently, using hair to measure long-term cortisol levels is becoming more popular. It is known that scalp hair grows, on average, one centimeter each month.

“Hair cortisol is a relatively new measure which offers a suitable and easily obtainable method for assessing chronically high levels of cortisol concentrations in weight research and may therefore aid in further advancing understanding in this area,” Sarah Jackson, researcher at the University College London, said.

During the experimental process, the researchers collected hair at least two centimeters in length and 10 milligrams in weight. The hair was cut as close to the scalp as possible in order to accurately capture the cortisol accumulation over a two-month period. On top of that, data of the subject’s body mass index (BMI), weight and waist circumference were also measured.

Jackson and her research group wrote in their article that hair cortisol level is correlated with body weight, BMI and waist circumference, and that higher levels of cortisol were associated with being more overweight.

“These results provide consistent evidence that chronic stress is associated with higher levels of obesity,” Jackson said. “People who had higher hair cortisol levels also tended to have larger waist measurements, which is important because carrying excess fat around the abdomen is a risk factor for diabetes and premature death.”

The team proposes that the hypothalamic-pituitary-adrenal (HPA) axis, which regulates cortisol levels, could be responsible for the development of obesity. Cortisol plays a broad range of roles in the human body, including glucose metabolism and anti-inflammatory responses.

Despite the numerous strengths of this study, such as the large sample number and use of hair to assess cortisol levels, there are limitations as well. The data from this study were collected from an older population with an average age of 69.72 instead of a younger population, which could have different cortisol levels.

This study also cannot provide evidence to explain whether elevated levels of cortisol are a cause or consequence of obesity.