Bacaan 9. Question 53 - 56 are based on the following passage.

    The study's findings are important because they use a biological marker to show a direct link between chronic stress and heart disease. Stressors, such as marital or financial troubles, have been linked to heart disease, but doctors could only rely on questionnaires to determine people's stress level. This study looked at more objective, measurable sign the level of cortisol, a hormone released during stress that shows up in the hair shaft. Measuring cortisol levels in hair also can indicate how long a person has been stressed, says Gideon Koren, one of the study's authors and a toxicologist at the University of Western Ontario. Cortisol, which is secreted by the adrenal glands, also shows up in urine and saliva, but that only shows stress at the moment of measurement not over long periods of time.

    "Hair grows about one centimeter (a fraction of an inch) a month, so if we take a hair sample six centimeters (2.6 inches) long, we can measure the cortisol level and determine stress level for the past six months," Koren says.This is critical, he adds, "because what kills is chronic stress."

    In the study, researches took 3-centimeter hair sample from 56 male heart attack patients admitted to Meir Medical Center in Israel. Hair samples were also taken from a control group, hospitalized for reasons other than a heart attack. The group did not differ significantly in terms of diabetes, high blood pressure, smoking, and a family history of heart disease.

53. Based on the passage, it can be inferred that ____.