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Go a few nights without enough sleep and you're more likely to get sick, but scientists have no real explanation(1) for how sleep is related to the immune system(2). Now, researchers at the Stanford University School of Medicine are finding that fruit flies(3) can point to(4) the answers.

What they have learned thus far(5) is that illness and sleep disruption(6) may be a two-way street(7): sick flies can't sleep, and losing sleep(8) makes them more susceptible to infection(9).

"When flies get sick, they stop sleeping," said David Schneider, PhD, assistant professor(10) of microbiology(11) and immunology(12). "Disrupting(13) sleep in turn(14) disrupts the immune system, which makes them even more infected(15) and it's downhill from there(16) in a 'spiral of death(17).'" Schneider is the senior author(18) of a study on the sleep patterns(19) of flies published in the May 15 issue of Current Biology.

Schneider worked with postdoctoral scholar(20) Mimi Shirasu-Hiza, PhD, who is the study's first author(21), to examine the connection between illness and sleep patterns by infecting fruit flies with one of two bacteria(22) -- Streptococcus pneumoniae(23) or Listeria monocytogenes(24).

The infected flies lost their "day" and "night" patterns of activity, which are part of the regular changes that occur(25) in the course of a day(26), called circadian rhythm(27). Uninfected(28) flies alternate between(29) 12 hours of high activity(30) and 12 hours of low activity(31). The researchers found the sick flies had fewer sleep sessions(32) and shorter periods of continuous sleep(33) than did healthy flies. They basically just didn't sleep well, concluded the researchers.