Levels of cortisol have previously been measured in blood, urine, and saliva, but these measurements of cortisol only provide a snapshot of stress. Levels of cortisol in hair shafts, however, can provide a longer-term assessment of stress levels. Hair grows about 1 centimeter a month, so a 3-centimeter hair sample, for example, is a marker for stress over three months.
In the new stress study, hair cortisol levels were actually a more important predictor of heart attack risk than other known heart disease risk factors such as smoking, hypertention (high blood pressure), and high cholesterol.
"We felt that stress was a minor factor compared to the other known risk factors for heart disease, but we didn't think it would be the strongest of them all," says study researcher Stan VanUum, MD, PhD, an associate professor of medicine at the Schulich School of Medicine & Dentistry at the University of Western Ontario in London, Canada.
Our body's fight-and-flight response is designed to help us out when we are in peril. Sudden spikes of cortisol can do just that, but when our increase of cortisol is chronic, it can have negative effects on our health.
Hair Cortisol Levels and Heart Disease Risk
Elevated cortisol can cause increases in blood pressure, blood sugar, body fat, and blood clotting -- all of which are known risk factors for heart attack.
In the new study, researchers compared 3-centimeter hair strands from 56 men who were hospitalized after a heart attack to hair strands from men who were hospitalized for conditions other than a heart attack.
The men who had heart attacks showed higher levels of cortisol in their hair shafts than men who did not have heart attacks, even after researchers controlled for other known risk factors for heart disease.
Both groups had similar rates of certain heart disease risk factors such as smoking, diabetes, high blood pressure, and family history of heart disease, but the men who had heart attacks did have higher blood levels of low density lipoprotein or "bad" cholesterol levels, and higher body mass indexes (BMI), than their counterparts who did not have a heart attack. In addition, men who had heart attacks also had lower levels of high density lipoprotein or "good" cholesterol levels.