A recent study found that oral contraceptive use in women could be associated with changes in gut microbial richness and gas production, with effects varying by menstrual cycle phase.
Researchers included 65 women aged 18 to 25 and compared oral contraceptive (OC) users with nonusers by analyzing fecal and breath samples collected on days 2 and 21 of the menstrual cycle. They used 16S rRNA gene sequencing to assess the gut microbiome and measured exhaled hydrogen (H₂) and methane (CH₄) concentrations using a 10-g lactulose breath test protocol over a 2-hour period.
While overall microbial diversity didn't differ significantly between the groups, a group-by-day interaction was found for observed features (OF), a measure of species richness, on day 21 (P = .04). The OC effect on OF was more pronounced on day 21.
Breath test data showed that the interaction between OC use and menstrual cycle day significantly influenced both H₂ and CH₄ production (P < .001 for both gases). Neither OC use nor menstrual day alone explained the observed gas concentration changes. H₂ and CH₄ levels were positively correlated (ρ = 0.724, P < .001).
Specific taxa were enriched among OC users, including Lachnospiraceae, Barnesiella, Faecalibacterium, and Clostridium species. Some of these taxa were also correlated with gas levels. Barnesiella was positively associated with CH₄, while Lachnospiraceae UCG010 was negatively correlated with both H₂ and CH₄.
Samples were further categorized by gas output. Higher H₂ levels were associated with increased abundances of Allisonella and uncultured Clostridiales, while lower CH₄ levels were linked to taxa such as Phocea and Bacteroides vulgatus. Methanobrevibacter smithii, a known methanogen, was not significantly enriched in high-CH₄ producers but was positively correlated with the CH₄:H₂ ratio.
“The random effect explained a larger proportion of the variance compared to fixed effects,” said lead study author Fernanda Terrazas, of the Department of Biology at San Diego State University, and colleagues, indicating that individual variability played a considerable role in breath gas production.
“Our LMEM revealed a statistically significant interaction between OC users and day on H₂ levels,” the study authors wrote.
Cycle-dependent changes in microbial richness and gas production were observed in OC users, underlining the influence of exogenous hormones on gut microbial dynamics.
While gastrointestinal symptoms weren't measured in this study, the researchers referenced prior findings linking hydrogen and methane to symptoms such as bloating and altered bowel habits. They recommended future studies explore how hormonal contraceptive–related microbiome changes may affect long-term health and gastrointestinal function.
Methanobrevibacter smithii, though infrequent in sequencing data due to primer limitations, was identified and may warrant further study. “Archaea in our samples may be of potential significance,” the study authors added, emphasizing the need to include archaeal-specific primers in future work.
The authors declared no conflicts of interest.
Source: Journal of Medical Microbiology
