Influence of menstrual cycle and oral contraception on taxonomic composition and gas production in the gut microbiome

<b>Introduction.</b> Oral contraceptives (OCs) are widely used for birth control and offer benefits such as menstrual cycle regulation and reduced menstrual pain. However, they have also been associated with an increased risk of cancer and reduced bone mass density.<b>Gap Statement.</b> While the gut microbiome is known to interact with endocrine factors, the impact of hormonal OCs on its composition and function remains underexplored. Additionally, we explore the relationship of OC use and the microbiome to gas production, which can cause symptoms and be indicative of poor health.<b>Aim.</b> This study investigates the effects of OCs on the diversity and composition of the gut microbiome and its association with breath hydrogen (H₂) and methane (CH₄) levels.<b>Methodology.</b> We utilized 16S rRNA gene sequencing to analyse faecal samples from 65 women, comparing OC users with non-users at two menstrual cycle time points. Breath tests measured hydrogen and CH₄ production. Data were analysed for microbial diversity, community composition and correlation with gas production.<b>Results.</b> There were no differences in overall microbial diversity between OC users and non-users in samples collected on day 2 of the menstrual cycle. However, on day 21, we found a significant difference in microbial richness, suggesting a cycle-dependent effect of OCs on gut microbiota species richness but not composition. We found a strong correlation between H₂ and CH₄ concentrations and an interaction between OC use and the menstrual cycle on H₂ and CH₄ production. We also identified several taxa associated with both high levels of H₂ and CH₄ production and OC use.<b>Conclusion.</b> Our study highlights the intricate relationships among hormonal contraceptives, the gut microbiota and gas production and connects shifts in the microbiome composition to gastrointestinal symptoms (e.g. gas production) that can impact overall health. This underscores the need for further research on the long-term effects of OCs and for the development of precise therapeutic strategies to address potential adverse effects. Our findings offer new perspectives on the microbiome-hormone-gas production nexus, potentially broadening our understanding of the systemic implications of OCs.