In response to a stressful event, it is normal for a person’s blood pressure to rise and then fall after the event. Now, new research indicates that excess body fat impairs the body’s ability to control blood pressure in this situation.

One key way that blood pressure is regulated is through the release of salt, or sodium chloride, in the urine, a process called natriuresis. In the current study, the amount of salt released in the urine dropped as body fat increased.

“Fitness facilitates the ability to regulate blood pressure; fatness impedes your ability to regulate blood pressure through your ability to regulate sodium,” study co-author Dr. Gregory Harshfield, from the Medical College of Georgia in Augusta, said in a statement.

The findings, which appear in the American Journal of Hypertension, are based on a study of body composition and natriuresis in 127 African American and white subjects with an average age of 16 years. Stress was induced by having the subjects play a competitive video game for an hour.

As expected, stress was associated with an increase in blood pressure and natriuresis, the authors note. The magnitude of these changes deceased as body fat rose. Further analysis showed that a person’s race predicted how high the blood pressure increased during stress.

“The major finding of this study is that body composition is related to the pressure natriuresis response to mental stress,” the authors conclude.

SOURCE: American Journal of Hypertension, November 2004.