New research suggests that the time you go to bed is just as important as how much sleep you get.

Researchers at Washington State University found that shifted mice from their usual cycle of sleeping and waking and saw that, while they got enough sleep, it was of poorer quality. The animals also had a disrupted immune response, leaving them more open to illness.

Previous studies on sleep usually focus on the effects of sleep deprivation or the overall amount of sleep an animal needs. The current study looks into the circadian process, a brain-driven clock that controls the rhythms of various biological processes, from digestion to blood pressure, heart rate to waking and sleeping. The cycle is found in most everything that lives more than 24 hours, including plants and single-celled organisms.

For the study, researchers used mice whose body clocks run at about 24 hours -- much like our own -- and housed them in a shorter 20-hour day. This forced their biological clocks out of sync with the light-dark cycle. After four weeks, the researchers injected the mice with lipopolysaccharide, a molecule found in bacteria that can make an animal sick without being contagious.

Researchers found that the disrupted animals had blunted immune responses in some cases or an overactive response in others, suggesting the altered circadian cycle made them potentially less able to fight illness and more likely to get sick.

"This represents a very clear dysregulation of the system," Karatsoreos said. "The system is not responding in the optimal manner."

Over time this could have serious consequences for an organism's health.

The mice on the 20-hour cycle were getting the same amount of sleep as they did on the 24-hour cycle. But the sleep wasn't as good. The mice woke more often and the pattern of electrical activity in their brains related to restorative sleep was greatly reduced.

The findings are detailed in the journal Brain, Behavior and Immunity.