A new study has found the first evidence that short periods of psychological stress can cause the body to take longer to clear heart-damaging fats from the bloodstream. Researchers at Ohio State University tested how quickly triglycerides - a type of fat linked to heart disease - cleared out of the bloodstream of volunteers during a stress-inducing test compared to a session in which the volunteers rested.
The results showed that, in all cases, stress caused triglycerides to stay in the bloodstream longer.
The findings suggest one reason why stress has been linked to heart disease, said Catherine Stoney, co-author of the study and professor of psychology at Ohio State University.
"If a person has a high-fat snack or meal during a time of stress, that fat is going to be circulating in the blood for a longer period of time," Stoney said. "That means it may be more likely to be deposited in the arteries where it can contribute to heart disease."
The study appears in the current issue of the journal Psychophysiology. Seventy healthy, nonsmoking middle-aged volunteers - half men and half women -- participated in the study. Half were between the ages of 40 and 48 and half were between 54 and 61. The two age groups allowed the researchers to consider both premenopausal and postmenopausal women during the project.
Each of the volunteers was tested twice, with both sessions occurring within three days of each other. In both sessions, an intravenous tube was inserted into the veins of the volunteers. A solution containing triglycerides - the equivalent of about 100 calories - was then intravenously administered. The procedure replicated what would happen in a person's bloodstream hours after they ate a meal containing fat, Stoney said.
In one session, the volunteers simply rested and their triglyceride level was checked continuously for 40 minutes. In the other session, the volunteers were administered the triglyceride solution and then given 40 minutes of stressful tests. The tests included having to prepare and give a videotaped speech, a difficult word problem task, a psychomotor task consisting of drawing mirror images, and a task where they had to quickly and accurately subtract two digit numbers from four-digit numbers. Again, their triglyceride level was monitoring continuously for 40 minutes.
In all 70 volunteers, triglyceride levels declined more quickly in the restful session than in the session where they completed the stressful tests, Stoney said. Overall, triglyceride levels declined an average of 2.8 percent a minute in the stress-inducing test session, compared to a quicker 3.2 percent per minute in the resting session.
In some people, the difference between the stressful and restful sessions was quite dramatic, Stoney said, while in others the differences in triglyceride levels were small. This reflects individual differences in how people metabolize fat. But it was significant that stress had negative effects in all the volunteers, she said.
"During stress, people are not metabolizing fat as rapidly and efficiently," Stoney said.
The study found that during the non-stress session, women cleared triglycerides out of their bloodstreams more quickly than did men. These findings were consistent with other research, Stoney said. However, the research found no difference in how quickly men and women cleared triglycerides during stress. ecause reproductive hormones might affect how triglycerides are cleared, the researchers separated pre- and naturally postmenopausal women. However, they found no differences in how these groups responded. In an additional analysis, the researchers also compared postmenopausal women who were taking hormone replacement therapy with those who were not. Again, they found no differences.