According to researchers, issues such as jobs, marital or financial problems are linked to an increased risk for developing cardiovascular disease, including heart attacks.

But until now a biological marker was not available to measure chronic stress and so predict -- several months in advance -- who may be most at risk of a heart attack.

"Traditionally, cortisol has been measured in serum, urine, and saliva. All of these matrices measure cortisol levels in the last hours to days and, therefore, do not reflect the stress response over prolonged period of time," said study authors Stan Van Uum and Gideon Koren of the University of Western Ontario.

But, cortisol is also captured in the hair shaft.

On average, hair grows one centimeter each month and so by examining a six-centimeter-long strand of hair, it is possible to determine stress levels over a longer period.

The researchers looked at hair samples from 56 men admitted for heart attacks to the Meir Medical Centre in Kfar-Saba, Israel and compared these to hair samples from 56 men hospitalized for non-cardiovascular health issues.

The heart attack patients were found to have higher cortisol levels in their hair.

And after accounting for known risk factors such as diabetes, hypertension, smoking and a family history of coronary artery disease, "hair cortisol content emerged as the strongest predictor of acute myocardial infarction," the study concluded.