Dr. Laura Klein, associate professor of biobehavioral health, who led the study, explains that our fight or flight response produces not only the familiar dry mouth, pounding heart and sweaty palms that accompany a stressful experience but also body chemistry changes that could result in health consequences.
Using doses of caffeine equivalent to drinking one to four cups of coffee and an intense arithmetic test as stressors, Klein and her colleagues found a rise in the amount of alpha amylase, an enzyme secreted by the salivary glands, in the healthy young men who participated in the study.
The results verified, based on performance, that a moderate dose of caffeine – 200 mg or about the amount in two cups of coffee – increased task performance and that doubling the amount of caffeine brings performance back down. The results also suggest that alpha amylase, which can be detected and measured via a new non invasive saliva test, provides a window on the biochemistry of the response not offered by cortisol alone which is commonly used to study the health consequences of stress.
The Penn State groups' results were detailed in a paper, "Effects of Caffeine and Stress on Salivary Alpha-Amylase in Young Men: A Salivary Biomarker of Sympathetic Activity," presented Thursday, March 2, at the annual meeting of American Psychosomatic Association Society in Denver, Colo. The authors are Klein; Courtney A. Whetzel and Jeanette M. Bennett, doctoral candidates in biobehavioral health; Dr. Frank E. Ritter, associate professor of information sciences and technology, psychology and computer science and engineering; and Dr. Douglas A. Granger, associate professor of biobehavioral health and human development and family studies.
In the study, 45 healthy men, ages 18 to 30, who had not had any caffeine- containing food or medications for at least four hours, came to the laboratory and provided saliva samples. Fifteen minutes after providing the saliva sample, they were given one of three doses of caffeine: none; 200 mg (equivalent to 1 to 2 cups of coffee) or 400 mg (equivalent to 3 to 4 cups of coffee). Then all the participants completed a mental arithmetic test.
Klein says, "The men had to count backwards from a four-digit number by sevens and thirteens. When they made mistakes, I corrected them and told them to go faster. This went on for 20 minutes."
Fifteen minutes after the test, the men provided another saliva sample. Their heart rate and blood pressure were also taken continuously throughout the testing period.
The researchers report that, as expected, blood pressure and heart rate increased in response to the arithmetic test and to caffeine. Alpha amylase levels in the participants' saliva also increased in response to caffeine and to stress, and these increases were positively associated with increased heart rate levels.
"Dependence and tolerance develop quickly to caffeine and other sympathomimetic substances, such as nicotine," Klein adds. "These new results suggest that alpha amylase, along with other novel biomarkers, may enable us to understand withdrawal and tolerance to sympathomimetics as well as providing a window on their health consequences."
The study was supported by a grant from the Office of Naval Research on which Klein and Ritter are co-investigators and by the Penn State General Clinical Research Center. Co-author Granger developed the new salivary alpha amylase assay with a team of researchers at his company, Salimetrics LLC. Salimetrics assayed the alpha amylase samples used in the study.