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Heart Disease Health Center

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Working Night Shift Affects More Than Your Social Life

WebMD Health News

Oct. 16, 2000 -- For 17 years, Ed Davis has worked from 10 p.m. to 8 a.m. because it allows him to work one week then be off the next. Although the schedule gives him the freedom to travel, his flexibility doesn't come without a price. By nature, the pharmacist at Harris Methodist Hospital is a morning person, and his work schedule has made him a chronic insomniac.

Fortunately, Davis apparently doesn't suffer from what some researchers say afflicts many people who work a shift schedule -- higher rates of accidents and cardiovascular disease. According to a study in the Oct. 17 issue of Circulation: Journal of the American Heart Association, weekly changes of sleep time affect the cardiac sympathetic and vagal, or parasympathetic, autonomic controls. The sympathetic nervous system accelerates body functions, including heart rate and digestion. The parasympathetic nervous system slows down some of these systems.

This means that the natural circadian, or daily, rhythms of your biological clock are constantly wrestling with your work schedule if you are required to work during the hours when your body and brain would normally be resting. The tug-of-war happens because your circadian rhythm and your lifestyle are not in synch. Circadian rhythms are, in part, tied to the 24-hour cycle of the Earth's rotation and the amount of daylight to which you're exposed.

According to the lead author of the study, Raffaello Furlan, MD, a professor at the University of Milan in Italy, "This resistance of the body's internal 'clock' to change with varied work schedules indicates that people don't adapt as easily as we think to shift work."

The researchers believe that the higher rate of sleep disturbances, gastrointestinal and cardiovascular diseases, and accidents that shift workers experience may be due to the stress that the frequent changing of sleep and awake periods places on the body's nervous system.

Max Hirshkowitz, PhD, director of the Baylor College of Medicine sleep research center in Houston, says that the biological clock is a strong force in determining people's sleep habits.

"There are three basic processes that govern and regulate sleep patterns -- circadian rhythms, homeopathic rhythms, and anything that activates the sympathetic nervous system and can interfere with sleep," Hirshkowitz tells WebMD. "For most people, it's more difficult to sleep during the day. Light is a stimulant. There is more noise during the day."

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