The levels of cortisol, a stress hormone, in one's hair can tell when a person is most likely to suffer a heart attack.

University of Western Ontario researchers, led by Gideon Koren and Stan Van Uum, developed a method to measure cortisol levels in hair and gauge stress levels in the months prior to a heart attack.

Cortisol secretion, which goes up during stress, has traditionally been measured in serum, urine and saliva, but that only shows stress at the time of measurement, not over longer periods of time, reports the journal Stress.

'Intuitively we know stress is not good for you, but it's not easy to measure,' explains Koren, professor of molecular toxicology at the University of Western Ontario.

'We know that on average, hair grows one cm a month, and so if we take a hair sample six cm long, we can determine stress levels for six months by measuring the cortisol level in the hair.'

In the study, hair samples three centimetres long were collected from 56 male adults who were admitted to the Meir Medical Centre in Kfar-Saba, Israel, following heart attacks.

A control group, made up of 56 male patients who were hospitalised for reasons other than a heart attack, was also asked for hair samples.

Higher hair cortisol levels corresponding to the previous three months were found in the heart attack patients compared to the control group.

After accounting for the known risk factors, hair cortisol content emerged as the strongest predictor of heart attacks.