Researchers in Britain say days of poor sleep can have a dramatic effect on the internal workings of the human body.
The activity of more than 700 genes is altered when people's sleep is cut to less than six hours a day for a week, changing the chemistry of their bodies.
Surrey University researchers analysed the blood of 26 people who each had up to 10 hours of sleep, then again after a week of less than six hours sleep each night.
The BBC reports heart disease, diabetes, obesity and poor brain function have all been linked to substandard sleep.
"Clearly sleep is critical to rebuilding the body and maintaining a functional state,'' Professor Colin Smith told the BBC.
"If we can't actually replenish and replace new cells, then that's going to lead to degenerative diseases."
He said many people may be even more sleep deprived in their daily lives than those in the study