Almost 20 percent of Americans now work the night shift, and many of them work in health care. Research shows numerous health risks are related to night-shift work — cardiovascular disease, diabetes, and obesity are all correlated with working shifts outside the normal 9 to 5.
What isn't known is the mechanism by which shift work adversely affects health. Researchers have hypothesized that the detrimental effects must come for the disruption of the brain's circadian rhythm. But a new Washington State University study shows that rhythms of internal clocks in digestive organs are disrupted by night work. Digestive organs' intrinsic rhythms were shifted by 12 hours after just three days of simulated night-shift work, while the biological clock in the brain only managed a two-hour adjustment during that period.
"We always thought the brain clock was sort of the master clock that told all the other clocks what time it is," says Hans Van Dongen, co-senior study author, director of the WSU Sleep and Performance Research Center and a professor in the Elson S. Floyd College of Medicine. "Now we've seen this really shocking result that, 'Wow, these body clocks outside of the brain adapt so fast.' That means you have these conflicting signals in the body."
More research is needed to show why the metabolic rhythms adjusted the way they did: It could be related to the sleep schedule, eating schedule or the level of physical activity, he says.
"That question becomes important when you start asking what can you do about it," Van Dongen says.
A 2007 study of night-shift workers showed their risk for metabolic syndrome was three times higher than those who worked day shifts. Metabolic syndrome is a combination of high blood sugar, excess body fat and abnormal cholesterol. It's closely related to insulin resistance, diabetes and cardiovascular disease.