People who suffer long-term stress may also be more prone to obesity, a new study has warned.

Researchers at University College London (UCL) in the UK examined 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.

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.

The 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 2cm long from each participant which was cut as close possible to a person's scalp – this represented about two months' hair growth with associated accumulated levels of cortisol.

They also examined the participants' weight, body mass index and waist circumference and how hair cortisol related to the persistence of obesity over time.

They 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).

Individuals classified as obese on the basis of their BMI (30) or waist circumference (102cm in men, 88cm in women) had particularly high levels of hair cortisol.

"These results provide consistent evidence that chronic stress is associated with higher levels of obesity," said Dr Sarah Jackson, who led the research.

"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 Jackson.

"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," she added.

The research was published in the journal Obesity.