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 that 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 that genes involved in inflammation, immunity and protein damage were activated, suggesting that 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 that the changes were so readily apparent after just one week.
According to the U.S. Centers for Disease Control and Prevention, 30 percent of civilian adults in the U.S. say they get six or fewer hours of sleep. That suggests that millions of people might be sustaining damage to their bodies.