Only over the last century have humans been exposed to such a huge alteration in the sleep-wake cycle that, previously, was dependent only upon the revolution of the earth in relation to the sun. With the advent of lighting and airplanes, the rhythms of daily life have changed for most of us, and have changed drastically for some of us who engage in shiftwork or who travel great distances on a regular basis via plane.
Might these alterations of daily life have an effect on the microbes living within our guts? And if so, might those alterations play a role on our health? Researchers from the Weismann Institute of Science set out to find the answers to these questions. In a study published in the journal Cell, the scientists determined that yes, disruptions in daily cycles do have an impact on gut bacterial composition and function, and those alterations trigger obesity and other metabolic abnormalities.
Shift workers and frequent flyers, especially those who cross numerous time zones on a regular basis, are more likely to suffer from obesity, diabetes, cancer, cardiovascular disease, and infections. The scientists wondered if gut microbes play a role.
The researchers first used an animal model to determine whether alterations in day-night cycles play a role on gut microbes. They found that changes in day-night cycles, powered by the circadian clock, triggered changes in gut microbial composition and function. Sixty percent of the gut microbe composition was altered (dysbiosis) in those mice who experienced a change in day-night cycle. They determined that these alterations were the result of an altered feeding schedule, and that they could be reversed by reverting to a feeding schedule that mimicked the normal day-night cycle.
Next, the researchers determined that these fluctuations of the gut microbiota triggered metabolic abnormalities such as fat accumulation and glucose intolerance (simply put, high blood sugar), which were ameliorated after administration of antibiotics, confirming the fact that the gut microbe dysbiosis was responsible for the metabolic abnormalities.
To test these effects in humans, they analyzed the gut microbes of two adults over the course of several days and found similar fluctuations in composition and function. Next, they analyzed stool of two adults who took a flight from the United States to Israel. They tested stool before the flight, 24 hours after the flight (jet lag), and two weeks after the flight. They found dysbiosis of the gut microbes under conditions of jet lag when compared to before the flight or two weeks after. Interestingly, they also found an abundance of the Firmicutes bacteria, which have been linked to obesity and metabolic abnormalities in humans.2
To take the study yet one step further, they transplanted stool from the dysbiotic, jet lagged humans into the digestive tracts of mice without gut microbes and found that those mice gained more weight and body fat and had higher blood sugar levels compared to mice that received stool from the individuals before and after being jet lagged.
“Our inner microbial rhythm represents a new therapeutic target that may be exploited in future studies to normalize the microbiota in people whose lifestyle involves frequent alterations in sleep patterns, hopefully to reduce or even prevent their risk of developing obesity and its complications,” noted the researchers. They recommend that “probiotic or antimicrobial therapy may be tested as potential new preventive or therapeutic approaches.”
Another recent study from the journal Clinical Gastroenterology and Hepatology found an increased risk of ulcerative colitis in people who get less than six hours of sleep per night. Ulcerative colitis is a severe digestive disease that involves inflammation of the colon and has been linked to gut bacterial imbalance. The results of this study are not surprising, given what we have just learned about the effects of the sleep-wake cycle.
The adverse health effects of sleep deprivation are widespread. Perhaps one day we will be able to combat these effects by improving our gut microbes without having to alter our poor sleep habits. Time and more research will tell.
- Thaiss CA, Zeevi D, Levy M, et al., “Transkingdom control of microbiota diurnal oscillations promotes metabolic homeostasis.” Cell. 23 Oct 2014;159(3):514–29.
- Ley RE, Turnbaugh PJ, Klein, et al., “Microbial ecology: human gut microbes associated with obesity.” Nature. 2006 Dec 21;444(7122):1022–3.
- Ridaura VK, Faith JJ, Rey FE, et al., “Gut microbiota from twins discordant for obesity modulate metabolism in mice.” Science. 2013 Sep 6;341(6150):1241214.
- Ananthakrishnan AN, Khalili H, Konijeti GG, et al., “Sleep duration affects risk for ulcerative colitis: A prospective cohort study.” Clin Gastroenterol Hepatol. 2014 Apr 26.