By Andrew M. Seaman
NEW YORK (Reuters Health) - Low levels of the hormone cortisol may identify teen drivers with a high likelihood of getting into car accidents, suggests a small new study.
Newly-licensed teens who produced high cortisol under stress were less likely to be involved in a crash or a near-crash, the researchers found. Measuring cortisol might make a good test to flag young drivers in need of extra safety training, they conclude.
"The theory is that people who have a heightened emotional response to certain stimuli may use that emotion to learn more effectively," Dr. Dennis Durbin told Reuters Health.
Durbin is the co-scientific director of the Center for Injury Research and Prevention at the Children's Hospital of Philadelphia. He co-wrote an editorial accompanying the new study.
"It really supports some other existing literature both in driving and non-driving areas that this cortisol level may play some role in how we actively learn from our experiences," he said.
Cortisol is released during stressful experiences and is involved in the so-called fight-or-flight response.
The researchers write in JAMA Pediatrics that traffic crashes are the leading cause of death for people 15 to 29 years old worldwide. Recent research has suggested that responses by the nervous system, such as cortisol production, may play an important role in crash risk.
In adults, the phenomenon of low cortisol levels in the presence of stress has been linked to risky, criminal and even asocial behaviors, they point out. It has also been linked to impaired and risky driving.
For the new study, Marie Claude Ouimet from the University of Sherbrooke in Quebec, Canada, and her colleagues recruited 48 newly licensed drivers from the U.S. state of Virginia.
The drivers were all 16 years old and had their probationary licenses for less than three weeks.
The researchers collected saliva samples from the teens while increasing their stress with a timed math test. The teens were told that the person with the most correct answers would win a cash prize. The saliva was used to measure cortisol levels.
The teens' cars were then outfitted with technology to record and report any crashes or near crashes they experienced during the following 18 months.
Overall, those who had the highest cortisol levels in the math test had lower crash or near-crash rates during those 18 months, compared to teens with the lowest measured cortisol.
The researchers also found that those with the lowest cortisol levels experienced a slower decline in their crash and near-crash rates over the 18 months, compared to teens with the highest cortisol levels.
The study can't say why crash rates differed between teens with different cortisol levels, Ouimet said.
"Let's say a driver does not experience much stress when involved in risky behavior - for example a crash or near crash," she said. "They don't experience much stress related to it and that may explain why you don't change over time and you don't learn from that experience."
Ouimet added that people with low cortisol levels may seek out risky driving, too.
"That may explain why they engage more in risky behavior," she said.
Durbin said there is no cortisol test on the horizon that can predict whether a teen will be a good or bad driver, but doctors and parents should still view driving as a health issue.
"The learning to drive process is not a conveyer belt," he said. "It really needs to be individualized for each teen."
SOURCE: http://bit.ly/1ipI8ET and http://bit.ly/1mYVM5V JAMA Pediatrics, online April 7, 2014.