Study might explain why health problems are more common among night workers
TUESDAY, Jan. 21, 2014 (HealthDay News) -- Sleeping during the day -- a necessity for jet-lagged travelers and those who work overnight shifts -- disrupts the rhythms of about one-third of your genes, a new study suggests.
What's more, shifted sleep appears to disrupt gene activity even more than not getting enough sleep, according to the research.
For the new study, which was published in this week's issue of the journal Proceedings of the National Academy of Sciences, British researchers put 22 healthy, young volunteers in a dimly lit sleep lab for three days.
During the first day, they disrupted the participants' sleep at regular intervals to reset their body clock to its innate rhythm. On the second and third days, the volunteers ate and slept on a 28-hour schedule, so their longest period of sleep was from noon until about 6:30 p.m.
The researchers drew blood samples all three days so they could watch what happened to the timing of gene activity.
During the first day, when the body reset its circadian rhythm, nearly 1,400 genes -- about 6.4 percent of all genes that were analyzed -- were in sync with that rhythm. On the days of shifted sleep, however, the number of genes tied to the body's clock dropped dramatically, to 228 genes, or only 1 percent of genes analyzed.
The researchers estimated that the sleep disruptions would ultimately impact about a third of a person's genes.
That's an even greater disruption than scientists saw in a previous study when they tested the effects of sleep deprivation on gene activity. In that study, which had study volunteers sleeping about five and half hours each night, the number of genes that were in sync with the body's clock dropped from about 9 percent to 7 percent.
"These are quite fundamental processes that are being affected," said senior study author Derk-Jan Dijk, a professor of sleep and physiology at the University of Surrey, in the United Kingdom.
"We think that may be related to the negative health outcomes associated with long-term shift work," Dijk said. Shift workers are at higher risk for many health problems, including obesity, diabetes, high blood pressure, heart disease, disrupted menstrual cycles and cancer, he said.
This study didn't directly connect health problems and night-shift work, but experts said it does start to help them understand why sleep might have such a powerful influence on a person's health.
"This study suggests that mistimed sleep can alter circadian rhythms, so the cycling of many, many genes is impaired," said Dr. Mark Wu, assistant professor of neurology, medicine, genetic medicine and neuroscience at Johns Hopkins University. "What this could cause, they can't really say -- except it's probably not good." Wu was not involved in the new research.
Genes carry the instructions for making proteins. Proteins make up just about every kind of chemical signal, hormone and tissue in the body, the researchers said.
The timing of when proteins are made is important because their production should correspond to our behaviors, said Frank Scheer, a neuroscientist at Harvard and director of the Medical Chronobiology Program at Brigham and Women's Hospital in Boston.
When the body anticipates a meal, for example, the liver has to stop releasing into the blood the carbohydrates it has stored and the pancreas has to make more insulin, while the muscles have to become more sensitive to insulin that's released so they can take in blood sugar, Scheer said.
"If these processes are working in concert and they're synchronized to when you eat and when you fast, then the system is very efficient and effective at absorbing these sugars quickly and minimizing any adverse consequences of elevated blood sugar levels," Scheer said.
"If these are not rhythmic, then you can easily imagine that, during the nighttime, you have this machinery up and running without need," he said. "During the daytime, when you actually do need it, it's only running half speed."
Visit the U.S. Centers for Disease Control and Prevention ( http://www.cdc.gov/niosh/topics/workschedules/ ) for more on sleep.
SOURCES: Derk-Jan Dijk, Ph.D., professor, departments of sleep and physiology, University of Surrey, United Kingdom; Frank Scheer, Ph.D., assistant professor, medicine, Harvard Medical School, and director, Medical Chronobiology Program, Brigham and Women's Hospital, Boston; Mark Wu, assistant professor, neurology, medicine, genetic medicine and neuroscience, Johns Hopkins University, Baltimore; Proceedings of the National Academy of Sciences, Jan. 20 to 24, 2014