The researchers in CHICAGO found that composition of a person’s intestinal microbial population differs from morning to night and from one month to the next. This individual shifts over time may explain why drugs don’t work the same in everyone.
Analysis of more than 18,000 timestamped stool samples collected worldwide indicated that centered log-ratio values (a measure of relative abundance) for different bacterial phyla and families commonly found in the gut microbiome varied substantially over the course of a single day, and also over a full year, according to senior investigator Amir Zarrinpar, MD, PhD, of the University of California San Diego.
Populations of some phyla, such as Actinobacteriota, tended to peak in the afternoon and evening. Others, such as Proteobacteria, were more abundant in the morning, with troughs later in the day.
Thus, at one point in the day certain types of bacteria may predominate but a wholly different composition may appear a few hours later. More than a third of phyla analyzed showed some degree of diurnal cycling after adjusting for confounding variables.
Similar patterns were seen across seasons: Proteobacteria hit their annual zenith in the summer and a winter trough, while a massive peak was found for Bacteroidota in late autumn and a nadir in late spring. The time plot for Verrucomicrobiota showed a double peak, in spring and again in the fall at a similar level.
Seasonal variations in temperature, humidity, and other environmental factors, likely drive these changes, with different types of bacteria responding in their own peculiar ways.
With regard to diurnal cycling, such influences are cited as “nutrient and water availability and sleep” as important factors.
These previously unsuspected shifts in gut bacteria might help explain why all people don’t respond to a particular drug in the same way, insofar as the microbiome is important in metabolizing them and can affect organ function in other ways as well.
The scientists always wonder why certain patients respond more robustly to some medications than others. In terms of performing clinical trials, especially if it’s a wide-ranging and multiyear study, it’s important to remember that perhaps there may be seasonal variations in response to a drug, and if so, it may be affected by something like the relationship of the microbiome, the host immune system, or post-metabolic processes.
The data show some regional and ethnic differences in the diurnal cycling patterns.
It is indicated that an important direction for future research is to examine whether the diurnal and seasonal variations correlate with individuals’ health status.
Prepared by: Nazila Kassaian
Reference
by John Gever, Contributing Writer, MedPage May 4, 2023
