It is well known that shift workers, those working outside the typical 9-5 schedule, suffer adverse health effects including greater rates of obesity, cardiovascular disease and cancer. Furthermore, half of American adults are sleep deprived, sleeping less than 5 hours per day. Sleep physiology plays a significant role in human health. What is unknown, is exactly how an atypical sleep schedule can have such a significant impact. The Gut Brain Axis may illuminate this link between sleep and host physiology.
The Gut Brain Axis is a complex system involving many factors including immune, endocrine, and hormonal factors, as well as bacteria, microbial mediators and the vagus nerve. Metabolic changes associated with altered sleep quality may be attributed to factors originating from the gut microbiome, including, but not limited to inflammation, low-grade endotoxemia, insulin resistance and increased intestinal permeability. A variation in the light/dark cycle has been noted to have an impact on the gut microbiome. An alteration in the light/dark cycle as experienced during jet lag is associated with an increase in the Firmicutes phyla. Partial sleep deprivation has been shown to alter the gut microbiome composition in as little as 48 hours, yet some studies have shown no effect. More research is needed in this area.
Sleep deprivation leads to inflammation, which has been associated with microbial dysbiosis. Cytokines IL-1β and IL-6 are strongly associated with sleep physiology. IL-6 is positively associated with microbiome diversity. IL-1β induces sleep and increases with sustained sleep loss. A decrease in sleep results in increased IL-6 levels. Chronic stress and intestinal mucositis have been shown to increase IL-1β and IL-6. Stress has been shown to decrease sleep quality and induce intestinal permeability. Evaluating the GI microbiome in populations suffering stress and sleep disturbances may prove most efficacious.
Seemingly benign jetlag, is associated with decreased gut microbial abundance and subsequent dysbiosis. Gut microbial diversity is positively correlated with sleep efficiency and total time slept. Abundant and diverse Firmicutes and Bacteriodetes phyla is positively associated with sleep. Lachnospiraceae have been found to be positively correlated with sleep efficiency and total sleep time. Lactobacillus rhamnosus has been associated with non-REM sleep, and supplementation has been associated with improved sleep quality, even after a stressful exposure. The Verrucomicrobia phyla has been linked to sleep physiology, as higher quality sleep has been associated with abundance of this phylum. A decrease in the number of awakenings during sleep has been associated with an abundant Actinobacteria phylum. Gut microbial balance is essential to a normal sleep cycle.
Sleep remains an underestimated component of health, and the gut microbiome may be a significant influence. Connections exist between the GI microbiome and sleep physiology. The Gut Brain Axis, variations in the light/dark cycle, inflammation, as well as microbiome abundance and diversity may elucidate factors linking the gut microbiome and sleep physiology. Addressing the Gut Brain Axis may be an avenue to support sleep in tandem with host physiology.
