“The seasonal variations we see in conditions like allergies or the flu occur in context of completely different microbiomes,” says Carolina Dantas Machado, Ph.D., the study’s lead author and a researcher in the laboratory of Amir Zarrinpar, MD, Ph.D., at UC San Diego. “We may need to put our understanding of how seasons affect health and disease in context of a microbiome that is much more variable and dynamic than we have previously thought.”
The researchers reviewed data from about 20,000 stool samples that were collected as part of the American Gut Project between 2013-2019. According to the researchers close to 60% of related bacteria have distinct 24-hour cycles, however, the seasonal differences were more obvious showing that certain types of bacteria followed specific patterns over the year.
In particular, the numbers of Actinobacteriota were found to be different depending on the time of day, being lower in the morning and significantly higher by the evening. A similar trend was found in levels of Proteobacteria according to the seasons being lower in winter months compared to peak summer months.
“You can imagine that the gut environment is radically different in terms of nutrient and water availability and pH when the person is sleeping compared to right after they eat breakfast,” explains Dr. Zarrinpar.
The researchers are not able to explain the reasons behind seasonal changes but are exploring climate and latitude data to see if light and temperature may play roles. The researchers are also looking for answers in other avenues such as exploring pollen and humidity as part of the equation because it is important to look at the whole picture when looking for answers.
These findings could be important for those studying the microbiome and to other research affected by the variation in the microbiome like medication studies involving the role it may have in metabolism, and researchers should be aware that the timing of stool sample collection could potentially influence research results in some unexpected ways.
