"We already know that under chronic stress, like illness, cholesterol levels go up," says Ohio State University psychologist Catherine Stoney, the lead author of the study. "And it was thought those increases were related to behavioral changes, like not exercising or poor eating habits."
"But now we have documented that cholesterol goes up -- and goes up very quickly, faster than could be related to behavioral effects, when people are subjected to acute stressors," she adds.Acute stressors in daily life could include getting stuck in traffic and worrying you'll be late for an appointment, or the anxiety you feel just before making a presentation at work.
"This finding could have potentially profound implications" in terms of focusing on the physiological as well as the behavioral reasons for higher fat levels in the bloodstream, Stoney adds.
The results of the study, which was sponsored by the National Institutes of Health and Ohio State's General Clinic Research Center, appear in the current issue of Psychophysiology.
Dr. Richard A. Stein, chief of cardiology at Brooklyn Hospital Medical Center and national spokesman for the American Heart Association, says, "This is an important study because it shows how clearing fatty acids from the bloodstream is altered by stress. It's one more little piece in the puzzle of the mind-body connection [between stress and heart disease]."
The study included 70 healthy, middle-age, nonsmoking men and women. The women were either pre-menopausal and post-menopausal. All the study participants' levels of triglycerides -- or fat molecules -- were 3.2 percent per minute when they were resting. Those levels declined an average of 2.8 percent a minute during stressful activities.
"Some people had a bigger difference [in the decrease of triglycerides] between resting and stress sessions, and some people had very little. But, there was remarkable consistency in that everyone had a slower decrease of triglycerides [during the stressful activities]," Stoney says.
While at rest, the women cleared the fats out of their systems faster than the men, a finding consistent with past studies. But there was no difference between women and men in the time it took to get rid of the fat molecules during stressful situations. Similarly, there was no difference between the pre- and post-menopausal women.
Stoney says one possible explanation for the slower decrease in fat levels during stressful situations could be that the body, ironically, is trying to become more efficient when it senses trouble.
"Since fat cells are used by the body as an energy source, it could be that stress slows down the rate at which the body gets rid of cholesterol," she says. The body is trying to conserve energy to meet the demands of stress.
"The body is wired to be able to provide energy needed to deal with stress. But in the distant past, the stressors were physical, like having to protect yourself from a wild animal," says Stoney.
"Today, the stressors are more mental than physical -- fighting with a boss, or dealing with some emotional issue -- and they don't require as much excess energy as a physical response," she says.
The result, she says, is that the fat, instead of being burned up to meet a physically stressful situation, remains in the bloodstream, potentially increasing the risk for heart disease.
For the study, volunteers had triglycerides injected directly into their bloodstream, a procedure that replicates how fat would reach the bloodstream a few hours after a meal.
The volunteers were then divided into two groups. One simply rested, while the other was given a series of stressful tests, like preparing and presenting a videotaped speech, and solving a difficult word problem test. The two groups spent 40 minutes in their respective activities, during which time blood samples were taken every five minutes to monitor triglyceride levels.
Each of the volunteers was tested twice, with the sessions occurring within three days of each other.
Stoney says the findings are too premature to make many specific recommendations for changing your personal habits.
"We don't know how [the findings] relate to [heart disease] risk," she says, which would have to be understood "before we make any recommendations."