A remarkable study pointing to gut microbiota involvement in jet lag was recently published in Cell by Elinav and colleagues : Transkingdom control of microbiota diurnal oscillations control metabolic homeostasis.
Until now, little recent evidence has linked sleep with gut microbiota. This study changes that. A major finding of Elinav’s group is that gut microbiota have a circadian rhythm, with gene expression and population numbers that cycle in circadian fashion:. For example Lactobacillus populations expand and contract in the gut microbiome, depending on the time of day:
This group showed that the gut microbiota follows a circadian rhythm, just like host cells. Moreover, they showed that healthy cycling microbiotas require a host that follows a normal circadian pattern of eating and sleep. When the mouse sleep and eating pattern is disrupted, their microbes lose their rhythm. When this “jet-lagged” microbiota is transplanted into germ free mice, the inoculated mice become fat and lose glucose control, that is, they exhibit a pre-diabetic state.
The investigators also studied humans who suffered jet lag. Two subjects with 10-12 hour time change gave fecal samples before, during, and after resolution of jet lag. The samples were inoculated into germ free mice. Lo and behold, the mice receiving jet-lagged poop became obese and pre-diabetic, exhibiting glucose intolerance:
I interpret these findings to mean that all our body’s activities, and those of our microbiota, have evolved to be on a timer. Mistimed sleep and eating has real consequences, increasing the risk of obesity, diabetes and many other diseases. In an editorial accompanying the Thaiss et al. paper, the question is raised whether similar changes in microbiota and metabolic control occur in humans who work night shifts. Coincidentally, our group at UNM is studying this very question. The UNM Department of Emergency Medicine is currently studying the effect of shift work on the microbiome and immune system. Since we emergency physicians work day shifts and night shifts: we are the shift-workers that we will be studying.