Stress is so much a part of modern day life that many people now take it for granted. But a new study has shown that stress can be bad for the heart, as it makes the body take longer to purge harmful fats from the bloodstream.
The research, carried out by scientists at Ohio State University, focused on triglycerides - a type of fat linked to heart disease - and how quickly they were cleared from the bloodstream after stress and in normal stress-free conditions. In every case, stress caused triglycerides to stay in the bloodstream longer.
This could be one of the reasons why stress is so often linked to heart disease, suggested 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."
Writing in the current issue of the journal Psychophysiology, Stoney said that her team had selected 70 healthy, non-smoking middle-aged volunteers, evenly divided between men and women, to take part 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 pre-menopausal and post-menopausal 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 administered intravenously. The procedure replicated what would happen in a person's bloodstream hours after they ate a meal containing fat, Stoney said.
In one session, volunteers simply rested while 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 monitored 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 per cent per minute in the stress-inducing test session, compared to a quicker 3.2 per cent per minute in the resting session.
In some people, the difference between the stressful and restful sessions was quite dramatic, while in others the differences in triglyceride levels were small, reflecting individual differences in how people metabolise fat, Stoney said. But it was significant that stress had negative effects in all the volunteers, she added.
The study found that during the non-stress session, women cleared triglycerides out of their bloodstreams more quickly than men. However, the research found no difference in how quickly men and women cleared triglycerides during stress.
Since reproductive hormones might affect how triglycerides are cleared, the researchers separated pre- and naturally post-menopausal women when testing, but found no differences in how these groups responded. In an additional analysis, the researchers also compared post-menopausal women who were taking hormone replacement therapy with those who were not. Again, they found no differences.