The study's findings are important because they use a biological marker to show a direct link between chronic stress and heart disease. Stressors, such as marital or financial troubles, have been linked to heart disease, but doctors could only rely on subjective questionnaires to determine people's stress levels. This study looked at a more objective, measurable sign — the level of cortisol, a hormone released during stress — that shows up in the hair shaft.

Measuring cortisol levels in hair also can indicate how long a person has been stressed, says Gideon Koren, one of the study's authors and a toxicologist at the University of Western Ontario. Cortisol, which is secreted by the adrenal glands, also shows up in urine and saliva, but that only shows stress at the moment of measurement — not over long periods of time.

"Hair grows about one centimeter [a fraction of an inch] a month, so if we take a hair sample six centimeters [2.6 inches] long, we can measure the cortisol level and determine stress levels for the past six months," Koren says. This is critical, he adds, "because what kills is chronic stress."

In the study, published last month in the journal Stress, researchers took 3-centimeter hair samples from 56 male heart attack patients admitted to the Meir Medical Center in Israel. Hair samples were also taken from a control group, hospitalized for reasons other than a heart attack. The two groups did not differ significantly in terms of diabetes, high blood pressure, smoking and family history of heart disease.

After accounting for the known risk factors, the researchers found that hair cortisol content was an even stronger predictor of heart attack than cholesterol level or body weight. "Hair cortisol levels were significantly higher in the [heart attack] group" than in the control group, the study noted.

The study's authors acknowledge that the sample size — 112 adults — was relatively small, but Koren says the group is working on doing a larger study. "We would like to come up with a set of cortisol numbers for physicians to look at" that would indicate whether a person may be at risk for a heart attack. Although cortisol readings wouldn't replace traditional heart disease markers, like cholesterol, genetics and blood sugar, it would give doctors an additional tool in determining risk.

"It could also provide us with a means to address other stress-related conditions, like ability to get pregnant and longevity of life," Koren adds. "It could also help people realize that they need to decrease the stress in their life.

Candy Sagon writes about health and nutrition for the Bulletin.

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