The immune system's response to illness affects sleep and memory, according to a recent study.

Researchers from the University of Leicester found that Fighting off illness- rather than the illness itself- causes sleep deprivation and affects memory. They said sickness-induced insomnia is common because of link between brain and immune system.

"Think about when you are sick. Your sleep is disturbed and you're generally not feeling at your sharpest. Previously work has been carried out showing that being infected leads to exactly these behaviors in fruit flies," biologist Dr. Eamonn Mallon said in a statement.

Mallon said it can be the immune system itself that can cause these problems.

By turning on the immune system in flies artificially with no infection present, researchers reduced how long they slept and how well they performed in a memory test.

"This is an interesting result as these connections between the brain and the immune system have come to the fore recently in medicine," Mallon said. "It seems to be because the two systems speak the same chemical language and often cross-talk. Having a model of this in the fly, one of the main systems used in genetic research will be a boost to the field."

The key message of the study is that the immune response, sleep and memory seem to be intimately linked, Mallon said.

"Medicine is beginning to study these links between the brain and the immune system in humans. Having an easy to use insect model would be very helpful," he said.

The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC), Dr.Mallon carried out the study with Ezio Rosato (Genetics), Robert Holdbrook (Biology undergraduate) and Akram Alghamdi (Taif University, Saudi Arabia while a PhD student at Leicester).