Changing time zones by just a few hours or more sends the body's natural cycles of wakefulness and sleep into a tail spin. And while exhaustion and disrupted sleeping patterns are the most obvious symptoms of jet lag, travelers can also suffer from headaches, sweating, nausea and bowel problems. That latter issue—including diarrhea and constipation—might in part be explained by a new finding. The microbes living in our guts, it turns out, also suffer from jet lag when we force them to come along for the ride to a new time zone.
These findings come predominantly from tests of microbes in mice, not humans. But the scientists behind the work predict that the same or very similar would hold true for human travels. To figure out how an organism's microbiome reacts to a time change, researchers from the Weizmann Institute of Science in Israel subjected mice that were naturally nocturnal to an artificial time change by altering those rodents' usual schedule, Time reports.
The effects on the mice's microbiome were numerous. As Time reports, the microbes became lax at important duties such as DNA repair, growth and detoxification. Their communities also changed in composition, and the mice became more susceptible to weight gain and catching diseases. When the researchers transferred some of the jet-lagged microbes into the guts of other mice whose microbiome had been sterilized, Time continues, they found that those mice, too, suffered from problems like obesity.
Finally, the researchers took the study one step further, extracting microbes over a three week period from two people who had just arrived in Israel from the U.S. The bacteria in the jet-lagged people showed "startlingly similar" issues as the bacteria in the jet-lagged mice, Time writes. The team even went so far as to transfer those human microbes into other sterile mice, finding that “transferring the gut microbes from the point where jet lag was at its highest induced much more obesity and glucose intolerance,” the researchers told Time.
These problems, the scientists think, have to do with what and when we eat, writes Ed Yong on National Geographic. When we're jet lagged, we no longer feed our microbes at the normal time, and their own life cycles are disrupted. This applies not just to human travelers but also those who work at odd hours at night. As Yong points out, past studies have shown that those individuals are at a higher risk for issues such as obesity, diabetes and some types of cancer. "This study suggests that microbes (or rather, diet via microbes) might be involved in some of these connections," he writes. "But how big a role do they play, compared to other possible factors? No one knows."