Your circadian rhythms are a complex set of physiological activities that govern when you feel sleepy and when your eyelids naturally flutter open in the morning. If you've ever experienced jet lag, you've felt the acute effect of a circadian malfunction—that sluggishness happens when your body thinks you should be sleeping.
A study released today in the journal Cell might help us learn to control these rhythms. Looking into the guts of mice, researchers discovered that bacteria keep their own daily travel routines, moving through the intestines over the course of a day. During that migration, the bacteria change how they express their genes, which in turn changes the way the host's organs respond.
If traveling gut bacteria turn out to control the sleep patterns of humans, they could help researchers understand the health problems associated with the disruption of circadian rhythms, says study author Eran Segal, a computational biologist at the Weizmann Institute of Science in Israel. Segal became interested in the research when he learned that people working night shifts were more susceptible to metabolism-related diseases, such as obesity and diabetes. Over the past few years, his research team has been using mice to understand how gut flora behaves, particularly in relation to the sleep-wake cycle.
"Even though bacteria live in our gut and in the dark, they in fact show circadian rhythmicity," Segal says. His research found that by disrupting these microbial rhythms, they could induce obesity and glucose intolerance, symptoms similar to those of the night-shift workers.
In the new study, Segal's team discovered that through the day, bacteria was moving by a matter of microns (one micron is about one-hundredth the width of a human hair) either into or away from the mucous layer that lines the large intestine. Although seemingly minor, the shift changes the rodent's metabolism. This is likely due to a shift in the communication between the intestine and its resident microbes, Segal says.
The research may also provide a new way of thinking about what time of day patients take medication. The researchers looked specifically at acetaminophen, or Tylenol. Previous studies suggest has different levels of liver toxicity throughout the day. By using antibiotics to wipe the mice's gut bacteria, the researchers found that they also eliminated the fluctuations in toxicity. "The implication is that we should also be considering the activity of the bacteria in relation to when we take the drugs," Segal says.
More broadly, the authors write, their study and others like it could suggest a better way to prevent and treat medical problems, like obesity and diabetes, that are associated with disruption to the circadian clock.