LOS ANGELES -- Doctors know being chronically sleep-deprived can be hazardous to your health. Night-shift workers, college crammers and all the rest of us who get less than our fair share of zzz's are more likely to be obese and to suffer cardiovascular woes than people who get a consistent, healthful eight hours.
Now scientists have some new clues about how lack of sleep translates into disease.
After subjecting 26 volunteers to seven nights of insufficient shut-eye followed by a marathon all-nighter, researchers detected changes in the way hundreds of genes were expressed in their bodies. Some genes, including damage-inducing ones involved in stress reactions, were amplified. Others, including many that nurture and renew cells and tissues, were turned down.
"It's possible to see how that contributes to poor health," said Colin Smith, a genomics researcher at the University of Surrey in England and one of the senior authors of a report detailing the findings this week in the journal Proceedings of the National Academy of Sciences.
Scientists have long puzzled over the purpose of sleep. For years they focused on how it influenced the brain, said Derk-Jan Dijk, a sleep and circadian rhythm researcher at the same institution and the study's other senior author.
But epidemiologists noticed people who work early in the morning or late at night -- or who lack sleep in general -- have higher rates of diabetes, stroke and high blood pressure, among other ailments. And biologists have discovered that people who get poor sleep produce more of the stress hormone cortisol and the appetite-stimulating hormone ghrelin, among other biochemical changes.
"It used to be thought that sleep was by the brain, of the brain, for the brain," said Dr. Charles Czeisler, a Harvard Medical School researcher who is known for his examinations of how poor sleep affects people in a variety of everyday settings.
"Now it's recognized that it plays an important role in bodily functions."
To learn more about the biological mechanisms at work, Dijk, Smith and colleagues asked their study volunteers to complete two evaluations.
In one test condition, the subjects -- all healthy adults who did not suffer from sleep disorders -- were allowed to stay in bed for 10 hours on seven consecutive nights. Brain wave scans showed that they slept for an average of 8.5 hours each night, an amount considered sufficient.
In the other test condition, subjects were allowed to stay in bed just six hours a night for seven nights, and they got an average of only 5.7 hours of sleep.
At the end of each week of controlled sleep, the researchers kept subjects awake for 39 to 41 hours, drawing blood every three hours for a total of 10 samples.
Then they analyzed cells in the blood, looking at changes in RNA -- the molecule that carries out DNA instructions, creating the proteins that drive processes in the body.
They found losing sleep changed rhythmic patterns in the way genes turn on and off, disrupting the genes' circadian clock.
Also, overall, 711 genes were expressed differently when people were sleep-deprived: 444 were turned down, and 267 were amped up.
Further analysis revealed genes involved in inflammation, immunity and protein damage were activated, suggesting tissue harm was occurring after sleep deprivation. Many of the suppressed genes, in contrast, were involved in producing new proteins, cells and tissues. The balanced process of tissue renewal seemed to be disrupted by insufficient sleep.
Dijk and Smith said they found it striking the changes were so readily apparent after just one week.
According to the U.S. Centers for Disease Control and Prevention, 30 per cent of civilian adults in the U.S. say they get six or fewer hours of sleep per night. That suggests millions of people might be sustaining damage to their bodies.
-- Los Angeles Times