A study of heart attack patients offers an entirely new kind of evidence that stress kills. It found that most cardiac patients had had elevated levels of the stress hormone cortisol months before their heart attack occurred. And they found this by examining hair samples.

Previous studies linking stress and illness have largely relied on subjective information from questionnaires. This study suggests a more objective to measure stress.

Cortisol is a hormone that increases during times of stress. Some of it becomes trapped in head hair while the hair is still beneath the scalp and provides a picture of how much cortisol is circulating in the blood at the time.

Just over 30% of the low cortisol group were heart attack patients; nearly 70% of the high cortisol group were heart attack patients.

Once the hair emerges from the scalp, no more cortisol enters the hair (unless applied as a medication). So the amount of cortisol in a growing hair is an indicator of how much stress a person was under some time in the past.

Because hair grows at about one centimeter per month (an inch every two and a half months), it serves as a record of how much cortisol a person was making at specific times in the past. A hair sample taken two inches from the scalp is a record of how much of the stress hormone cortisol was circulating in a patient five months ago.

When cortisol is measured in blood, saliva or urine, it only tells how much cortisol has been circulating in the last few hours or days.

The study measured the amount of cortisol in hair samples taken from 56 male Israeli heart attack patients and 56 other male patients who had been admitted to the hospital for reasons other than heart attack or stroke. Hair samples were taken from patients 2-3 days after hospital admittance. A three-centimeter portion of hair closest to the scalp (the last three months of growth) was cut into two 1.5 cm sections, each of which was analyzed for its cortisol content.

The cortisol content in the heart attack patients' hair was on average, about 1/3 higher than that of the other patients (295 ng/g vs. 225). When all 112 patients were separated into four groups based on their hair cortisol content (lowest, two middle, highest), the percentage of heart attack patients rose steadily from the lowest cortisol group to the highest cortisol group. Just over 30% of the low cortisol group were heart attack patients; nearly 70% of the high cortisol group were heart attack patients.

This suggests that most of the heart attack patients had been under a high level of stress three months before their heart attack.

A statistical analysis of other patient information (age, cholesterol, smoking, etc.) found that patient hair cortisol content was the strongest predictive factor of the upcoming heart attack.

One problem with this type of study is that it can't tell whether increased cortisol (and stress) helped cause the heart attacks, or whether illness caused cortisol and stress to rise. One finding in this study hints at the first possibility: there was no difference in the cortisol content of the two 1.5 cm hair samples taken from the heart attack patients. That is, their cortisol level was the same 1.5 months and 3 months before their heart attack. This suggests that the rise in cortisol was not a short term event that occurred just before the heart attack.

The moral of the story seems to be that anything that lowers the stress in your life is probably good for your health.

An early online article detailing the study was published by the journal Stress on September 2, 2010.