An Israeli-Canadian study used hair to study stress hormone, and found, not surprisingly, that chronic stress plays an important role in heart attacks.
Cortisol, a hormone secreted in higher levels during times of stress, is usually measured in blood, urine or saliva. But those measurements reflect stress only at a certain period of time, not over long stretches.
Hair, however, captures cortisol levels over a longer period, said study author Dr. Gideon Koren.
Since hair grows a half-inch per month on average, a three-inch-long hair sample can show cortisol levels over six months, he said.
"It gives us, for the first time, a biological marker for chronic stress," Koren said.
The hair shaft records cortisol levels through time, similar to the way tree rings reflect age.
In the study, researchers collected 1.5-inch-long hair samples from 56 men admitted to the Meir Medical Centre in Kfar-Saba, Israel, suffering heart attacks or acute myocardial infarction (AMI).