New study looks into correcting sleep cycles

At Hopkins, seeing students studying into the early hours of the morning isn’t uncommon, but it’s probably unhealthy. All organisms, from bacteria to humans, have internal clocks to help them synchronize their behaviors to the time of day. A study just recently published in Cell suggests that the biological clocks in gut microbes living in mice and humans are controlled by their host’s circadian rhythms, and when hosts disrupt their circadian rhythms it can lead to health problems like obesity.

Circadian clocks help organisms coordinate their activities with daily as well seasonal changes in the day-night cycle. They are powered by biochemical mechanisms that run through 24 hour cycles by receiving signals, such as daylight or darkness, from the environment. These circadian rhythms can influence body temperature, appetite, and hormone secretion, and the clocks are “reset” when organisms sense external changes in the environment. The primary external time cue humans and other mammals follow is the light and dark cycle.

Jet lag, or circadian clock disruption, is the physiological condition where an organism’s circadian rhythms have been disrupted by rapid, long-distance travel, shift work or even pulling all-nighters for late night studying. This phenomena is common today – frequent fliers, shift works, and even students are all part of the population affected by circadian clock disruption. The temporary disorder has been linked to a rise in the incidence and severity of wide range of diseases, such as obesity, diabetes, cancer, and cardiovascular disease. But, until now, the mechanisms and causes for how changes in circadian rhythms increase the risk for these diseases have been unknown.

In the study conducted at the Weizmann Institute of Science, the researchers examined the microbiome in the fecal matter of mice and human subjects, and discovered that populations of bacteria fluctuate and change based on the time of day the sample was taken. In order to observe the effects of jet lag on mice, the scientists manipulated light sources and feeding times. They found that when the mice develop jet lag, the microbial population in the affected mice’s guts change and lose its rhythmic fluctuations. The jet-lagged mice even start to gain weight and develop metabolic problems compared to their control counterparts, even though the two were fed the same diet. When the researchers transferred the gut-bacteria from the jet-lagged mice into the control mice, the control mice began to develop the same issues, suggesting that the gut microbiome plays a role in the development of obesity and other metabolic diseases.

The two human participants, on the other hand, were sent on a flight from the United States to Israel. Their gut microbiomes were also changed – there was an increase in the growth of bacteria related to obesity and metabolic disease. Fortunately, their microbiomes were able to transition back into a healthy baseline after a few weeks.

For now, the researchers are looking into normalizing the gut bacteria in people whose lifestyles involve frequent disruptions in sleep cycles – probiotic or antimicrobial therapies could reduce or prevent the risk of developing obesity and other metabolic issues in individuals who are prone to circadian clock disruption.

The actual health implications still remain to be seen, but fortunately, there are already ways to help alleviate jet lag and adapt into a new schedule easier. Minimizing sleep distractions on airplanes or even at home by using eye masks or ear plugs will help you get a better night’s sleep in distracting environments, and taking a hot bath or shower right before bedtime can help induce sleepiness by dropping your core body temperature when you step out of your bath. Staying hydrated is also essential – preventing dehydration will help your body maintain homeostasis and adjust to changes easier. If you fly or experience circadian sleep cycle disruptions frequently, you could consider visiting a physician or psychologist specialized in sleep medicine.