Stress may make you want to pull out your hair, but those tresses could be the key to measuring just how much stress you're under, according to a new study.
The study found that the stress hormone cortisol can be measured in hair, providing the first long-term record of chronic stress that doesn't rely on a person's memories. High levels of cortisol in hair were associated with heart attacks, the researchers reported online today in the journal Stress. [Stress and 9 other Destructive Human Behaviors]
The findings could provide a new way to research chronic stress, according to the researchers. If the results can be replicated, the test may eventually be used in the doctor's office to identify people at high risk for cardiovascular disease.
A record of stress
The hair on your head is dead, but its follicle, or root, is alive. Substances like cortisol, which get released into the bloodstream when you're stressed, can seep into the follicle from the tiny blood vessels in the skin of the scalp. As the hair grows, traces of cortisol get trapped in the shaft, providing a way for researchers to measure the hormone over time. Because hair grows about 0.4 inches (1 centimeter) per month, most people have many months' worth of records of cortisol levels sitting on top of their heads. Previous measures of cortisol in blood or urine could record only a few hours' or days' worth of the hormone.
"[Hair] tells me what happened to you in the last 10 months," study researcher Gideon Koren, a professor of pediatric medicine and toxicology at the University of Western Ontario, told LiveScience. "I can even see how things change monthly."
Koren had previously used hair samples to measure drug toxicity in infants whose mothers used cocaine and heroine while pregnant. He learned that other colleagues were using similar methods to detect steroids in the systems of bodybuilders. If hair could accurately measure body-boosting steroids, he realized, it might also hold a record of other hormones, like cortisol. Previous research had found that the cortisol persists in the hair for at least six months, and in the case of several Peruvian mummies, up to 1,500 years.
Hair and heart attacks
To test the idea, Koren and his colleagues took hair samples from 120 men who checked into the cardiac unit of the Meir Medical Center in Israel. Half of the men were diagnosed with heart attacks, while the other half had other diagnoses like chest pain and infection. Only men were studied because heart attacks are more common in men, and because hormonal differences between men and women could skew the results.
The researchers analyzed the cortisol levels in the 1.2 inches (3 cm) of hair closest to the scalp, representing about the last three months of the patients' lives.
They found that cortisol levels were significantly higher in men who had heart attacks compared with men who had other illnesses. When the researchers split the men into quartiles based on their cortisol levels, they found that of the men with the lowest levels, 32 percent had heart attacks. In the men in the uppermost quartile of cortisol, that number jumped to 68 percent.
The results held even after controlling for other heart-attack risk factors like cholesterol levels and body mass index (a measure of body fatness).
"It's not the only one, of course, but cortisol is an important determinant of acute myocardial infarction," Koren said, using the technical term for heart attack.
Testing the test
The results will need to be replicated with larger numbers of patients before hair-cortisol testing goes mainstream, Koren warned. Other research has shown that cortisol levels in the hair do match cortisol levels in the blood, but Koren and his colleagues aren't yet sure if their results will apply to women. They also didn't test whether hair cortisol levels matched people's subjective feelings of stress.
If the test works, however, it could be a noninvasive way to measure stress over time. That's important, Koren said, because people's long-term memories of stress aren't always reliable.
"It could be another tool for us, if it's possible to do and not expensive," said Alicja Fishell, a psychiatrist at Women's College Hospital in Toronto. Fishell, who has collaborated with Koren before but was not involved in the current study, said the findings could one day prove useful to research in her area, reproductive health, because the effect of chronic stress on pregnant women and fetuses is not well-understood.
"We need to have a good study that really correlates" the relationship between stress and later psychiatric problems in women at different reproductive stages of life, Fishell said.
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.