Stress hormone measured in hair linked to persistent obesity, study finds Cortisol levels were measured via strands of hair collected years apart.

 -- People with long term stress may be more likely to be obese, according to a recent study by scientists at the University College London, and the telltale signs can be found in strands of hair.

The paper published today in the journal Obesity found that people who have a higher level of the stress hormone cortisol, which affect's the body's metabolism and how it distributes fat, over a long period of time may be more likely to be obese. Their levels of cortisol were measured through hair samples.

This study is part of growing body of evidence linking stress and excess weight gain, including obesity, which is linked to higher risk for heart disease and cancers, according to the World Health Organization.

"We don’t know what is the true relationship between stress and obesity," Sarah Jackson, a research associate at the Institute of Epidemiology & Health at the University College of London. "We know there’s a relationship there but we don’t know if it’s stress causing obesity or obesity causing stress."

To better understand the long-term relationship between weight and stress over time, researchers looked at information from multiple 4-year periods starting in 2002. They compiled data on cortisol and body measurements from 2,527 men and women between the ages of 54 and 87 who were participating in the English Longitudinal Study on Ageing.

Cortisol levels were examined in study participants' hair at 2 time points, 4 years apart to determine the relationship between persistent obesity and hair cortisol levels.

Researchers cut a lock of hair from each participant as close to the scalp as possible. Hair grows approximately 1 cm a month and 2 cm of hair was obtained to represent two months of time. Measurements of hair cortisol levels, as well as body height, weight, and waist circumference were taken to determine obesity trends over time.

Scientists found those who had higher hair cortisol levels had a tendency to be larger and weigh more. In general, they also had the largest waists, were the heaviest in weight and had the highest body mass indexes (BMI).

Those considered to be obese or having a waist greater than 44 inches in men or 34.5 inches in women had the highest levels of stress hormone compared to other subjects.

The study authors acknowledge that the findings are preliminary and a vast majority of the subjects studied so far, 98 percent, where white and British. The data were also from people older than 50 and from only the most recent assessments since tests for hair cortisol have been established.

While preliminary, Jackson said the findings may help encourage people to take steps to diminish stress in their life.

"Just try to be aware of lifestyle at times of stress," said Jackson. "Really we need to have people get up and be active."

She added that finding constructive ways to handle stress could also help mitigate the body's response to it.

"It could be good to reduce their exposure to stress or finding coping situations to stress, to be able to manage it more effectively."

The study findings do not prove that stress causes obesity, but do add to past evidence that they are linked, according to Dr. David Katz, director of Yale University Prevention Research Center.

"We have long had a large body of evidence implicating chronic stress and its hormonal effects with elevated body fat," said Katz. "So the association is certainly plausible."

Katz said there continues to be a tremendous amount of evidence that chronic stress is a serious factor in determining overall health, adding that the closely associated hormone, cortisol, "contributes to adipose tissue gain and obesity in particular."

"From the weight of evidence, it is rather clear that chronic stress is both bad for health in general," Katz said, "and due in part to effects on cortisol."

Dr. RAJIV BAHL is a Chief Resident Physician of Emergency Medicine at the University of Toledo Medical Center and a medical resident in the ABC News Medical Unit.

ABC News' Gillian Mohney contributed to this report.