Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, January 5, 1992 TAG: 9201050018
SECTION: NATIONAL/INTERNATIONAL PAGE: A-3 EDITION: METRO
SOURCE: Associated Press
DATELINE: WASHINGTON LENGTH: Medium
SHIFT WORK CALLED BAD FOR HEART
Shift work may endanger your health, Agriculture Department scientists say.The researchers reached that conclusion after subjecting laboratory rats to constantly changing, random cycles of light and dark.
Their findings: The target rats developed far higher levels of cholesterol than did rats exposed to 12 hours of light and 12 hours of darkness on a constant schedule.
"The findings may explain why, among humans, shift workers appear to have more cardiovascular disease than day workers," said Dr. Leslie M. Klevay, research medical officer with the department's Agriculture Research Service in Grand Forks, N.D.
In their experiments, Klevay and Edward S. Halas, a psychologist at the University of North Dakota, turned off and on the lights on their rats at different times every two to four days.
Klevay and Halas studied the effects of these light changes. They also researched the changes that took place when the rats were given diets low in copper. Copper deficiency is known to increase cholesterol in rats and to heighten heart problems in humans.
After six weeks, cholesterol levels were found to be 24 percent higher in rats given light in random on-and-off doses.
"This suggests bad news for people who work variable shifts," Halas said.
For the rats fed low-copper diets while living in an environment with random periods of light and dark, the news got worse. Their cholesterol reached levels 70 percent higher than for the control animals, the researchers said.
For rats fed the low-copper diets but not subjected to random periods of light and dark, cholesterol levels were 33 percent higher.
Klevay and Halas noted that previous research has found that in night workers the natural day-night rhythms in heart rate, respiration and metabolism never readjust.
"Not only does shift work disrupt these circadian rhythms but it may also increase risk factors for cardiovascular disease," Halas said.