People who suffer long-term stress may also be more prone to gaining extra kilos overtime, says a study.

The findings, published in the journal Obesity, are based on examination of hair samples for levels of cortisol, a hormone which regulates the body's response to stress. The study showed that exposure to higher levels of cortisol over several months is associated with people being more heavily, and more persistently, overweight.

"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 heart disease, diabetes, and premature death," said lead researcher Sarah Jackson from the University College London.

 

"These results provide consistent evidence that chronic stress is associated with higher levels of obesity," Jackson added. Chronic stress has long been hypothesised to be implicated in obesity -- people tend to report overeating and 'comfort eating' foods high in fat, sugar and calories in times of stress, and the stress hormone cortisol plays an important role in metabolism and determining where fat is stored.

Previous studies looking at the link between cortisol and obesity relied mainly on measurements of the hormone in blood, saliva or urine which may vary according to the time of day and other situational factors. These studies failed to capture long-term cortisol levels. This research involved 2,527 men and women aged 54 and older taking part in the English Longitudinal Study of Ageing, taking data over a four-year period. In the research, the scientists took a lock of hair two centimetre long from each participant which was cut as close possible to a person's scalp. This represented approximately two months' hair growth with associated accumulated levels of cortisol. The researchers found that people who had higher levels of cortisol present in their hair tended to have larger waist circumference measurements, were heavier, and had a higher body mass index (BMI).