November 23, 2010
An estimated 20 percent of the American workforce does some type of shift work. This doesn’t have to mean working the graveyard shift. It can mean any work done between 7 p.m. and 7 a.m.
Most sleep doctors agree that working at night, from a biologic point of view, is not natural for human beings. We have evolved to be active in the daytime and to sleep at night. In fact nearly every cell in our body has a circadian rhythm, meaning that biological processes have a 24-hour cycle. And this is how we lived for thousands of years, until the invention of the lightbulb, which has allowed us to separate our activities from the rhythm of the sun, but at our own peril.
Some people can shift their sleep-wake schedule fairly easily. Others have a very hard time sleeping in the daytime and are very tired when they need to be awake. Such people suffer from “shift work disorder,” which is classified as a circadian rhythm disorder by the International Classification of Sleep Disorders-II. Although we have good estimates for the number of shift workers, we don’t have good data yet on how many actually suffer from shift work disorder.
More and more research is showing the consequences of shift work. It has been linked to work-related and traffic accidents, to psychiatric and GI illness and even to heart disease and cancer. In fact, The International Agency for Research on Cancer (a subcommittee of the World Health Organization) published a statement in 2007 that classified shift work as a “probable carcinogen.”
So how could shift work be linked to heart disease? Experimental studies have shown that when people sleep in the day instead of at night, they tend to have higher blood pressures during sleep. They also reverse their normal cortisol rhythm, the ebb and flow of the body’s natural stress hormone. They have a decrease in leptin, which is the hormone that helps make you feel full. They also have increased levels of glucose and insulin to such an extent that in a matter of days, normal people can develop pre-diabetes just by staying up at night and sleeping in the day.