In "What Your Hair May Say About Your Heart," AARP.org reports on a study that found that testing samples of a person’s hair may reveal if that person is more likely to have a heart attack. According to AARP.org, these are significant findings because studies that rely on patients to provide information about stress level may not have the most accurate information. In contrast, "This study looked at a more objective, measurable sign — the level of cortisol, a hormone released during stress — that shows up in the hair shaft."
While cortisol levels can be measured using urine and saliva, using these to test for stress will only indicate how stressed a person was when they were tested and won't inform doctors if the person has a history of continued feelings of stress.
Because hairs grows over time, if you take a sample that would be representative of hair growth over a number of months, the cortisol present may indicate ongoing stress. In fact, "the researchers found that hair cortisol content was an even stronger predictor of heart attack than cholesterol level or body weight.”
The sample used for this study was small (112 adults—56 were male patients who'd suffered a heart attack ad the rest were a control group with other medical conditions) but the findings were interesting. A doctor would not use cortisol levels found in a hair sample as the only indicator that a person is susceptible to a heart attack, but when used with other tests, it could indicate the need for lifestyle changes.
Whether or not further studies conclude that this is a viable way to test for heart attack risk, you can find ways to reduce stress so you can keep your heart healthy and strong.