by Dennis Thompson
HealthDay Reporter
FRIDAY, April 28, 2023 (HealthDay News) — Half the cells in your body aren’t human, and a new study suggests that many critics of your health fluctuate by hour, day and even season.
The human body contains about 40 trillion bacteria, viruses and fungi, creating a microbiome roughly equal to the number of human cells, said researcher Dr. Amir Zarrinpar, an assistant professor of gastroenterology at the University of California at San Diego. .
His team found that the microbes in the gut microbiome are constantly changing throughout the day, and even change with the seasons, Zarrinpar said.
“These findings offer important insights into the role of the changing gut microbiome in health and disease,” Zarrinpar said during a press briefing on the findings. “They can potentially explain why we are predisposed to seasonal diseases and whether the microbiome prepares us for it. And not only that, they can influence how researchers study the microbiome and how our research might be affected by these variations in the microbiome.”
Zarrinpar plans to present the findings on May 7 at the Digestive Disease Week meeting in Chicago. Findings presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.
For the study, Zarrinpar and his colleagues reviewed data from about 20,000 stool samples collected as part of a global microbiome research effort called the American Gut Project.
The researchers looked at the specific time, date, and location of each sample, and used that data to determine how much the composition of the gut microbiome can vary.
The researchers found that almost 60% of the related bacterial groups fluctuate with a cycle other than 24 hours.
“We don’t have a clear cause for what contributes to these daily fluctuations, but we surmise that diet and sleep are probably the main contributors to this,” Zarrinpar said. “This is likely because the gut environment is radically different in terms of nutrient and water availability and pH when a person is sleeping compared to just after breakfast.”
The seasonal fluctuations were even more pronounced, with certain types of bacteria following one of two distinct patterns over the course of a year, the researchers said.
For example, a family of bacteria called proteobacteria dipped steadily to low levels during the winter, then rose steadily to peak in the summer, Zarrinpar said.
“What really took us by surprise was the seasonal variation. We didn’t expect the seasons to have such a tremendous effect,” she noted.
“While that has been reported in hunter/gatherer societies in Africa, it hasn’t really been reported in industrialized countries,” Zarrinpar continued. “Finding an effect much more pronounced than the daily variation really took us by surprise.”
Seasonal fluctuations could be influenced by location, weather, pollen, humidity and other environmental factors, he suggested. These findings could offer a possible explanation for why humans are more susceptible to colds and flu during specific seasons, as the microbiome is known to influence the immune response.
The fluctuating microbiome also plays a role in how drugs are metabolized and therefore could skew clinical trial results unless accounted for, Zarrinpar said.
“As physicians and scientists, we always wonder why certain patients respond more robustly to some drugs than to others. I think as far as conducting clinical trials, it’s important to remember that, especially if there’s a large, multi-year study, there might be seasonal variations in response to a drug,” he said.
“An interesting thing that we have thought about is that the responses of patients to the COVID vaccine differ depending on the time of day that they received the vaccine,” Zarrinpar added. “Certainly, since the microbiome is such a tremendous influencer on immune response, we wonder if these variations play a role in something like vaccine response.”
This could explain why studies on the potential benefits of probiotics and prebiotics have ended with mixed results, Zarrinpar said.
“Because the landscape into which these agents are introduced fluctuates and there may be times of the year or day when the microbiome may be more receptive to manipulation or where drug metabolism functions are more available, this could have many implications. Zarrinpar said.
Dr. Loren Laine, chair of this year’s Digestive Disease Week, called the microbiome study “important and interesting.”
“The idea that it’s some kind of stable population that stays the same is not really true,” said Laine, section chief for digestive diseases at the Yale School of Medicine in New Haven, Connecticut. “It changes drastically with diet, with the use of medication, and obviously with different times of the day.”
More research is needed to identify important parts of the microbiome and how they fluctuate, Zarrinpar and Laine said.
“The clinical implications will still be waiting to be seen at this point,” Laine said.
More information
The Cleveland Clinic has more about the gut microbiome and your health.
SOURCES: Amir Zarrinpar, MD, PhD, assistant professor, gastroenterology, University of California, San Diego; Loren Laine, MD, section chief, digestive diseases, Yale School of Medicine, New Haven, Conn.; May 7, 2023 presentation, Digestive Disease Week meeting, Chicago
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