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."
Your biological clock tells you that the sleepiest time of the day is 4 a.m., Hirshkowitz says, yet many shift workers drink coffee around that time to stay awake. "Then they can't go to sleep, or they sleep but wake up a short time later," he says. "It's equivalent to drinking coffee after dinner."
Shift workers often develop odd or destructive habits like trying to change their sleep habits on the weekends because they want to be with their friends. According to Hirshkowitz, this is the wrong thing to do. "It creates a cycle of sleep deprivation," he says.
He advises that if you have to work a night shift, you should keep your sleep patterns the same on your days off, and you should protect the time when you're supposed to sleep. If you have to change shifts constantly, you also protect your sleep time; don't exercise within two hours of trying to sleep, but do exercise; use blackout curtains. In other words, practice what Hirshkowitz calls "sleep hygiene."
Circadian rhythms also seem to control the amount of and time when various hormones are released in the body, such as cortisol, growth hormone, and testosterone. Because the release time of these substances might not match your schedule, it can lead to health problems, the Italian researchers say.
Hirshkowitz says it's easy to see these effects. "What happens if you haven't had enough sleep? With sleep deprivation, your balance is off, you have gastrointestinal upset, your eyes ache, and you're more prone to colds," he tells WebMD.
As for Davis, he knows that he needs more sleep, but he's not ready to take the step to correct his chronic sleep deprivation. "Basically, I either live with it or find another job," he says.
"I'm a day person, and I like to go to bed early and get up early," he says, adding that the first five years he worked this shift, he didn't have a problem with going from night sleep to day sleep. But now he does. The experts would tell him that his pattern of sleeping during the day on weeks he's working then sleeping at night on the weeks he's off are causing his insomnia -- and could be seriously affecting his health.
Davis knows this, too, because of his training in the health care field. "If I didn't work a night shift, it probably would be better for my cardiovascular system," he says. "I'm probably cutting years off of my life."