Abstract
BACKGROUND: Ammonia (NH(3)) and hydrogen sulfide (H(2)S) are produced during digestion in the human gut, yet the impact of these internally generated gases on male reproduction have received limited attention in scientific research. METHODS: We systematically reviewed 935 scientific publications, spanning from 1947 to 2023, focusing on external or internal NH(3) and/or H(2)S, male infertility, and gut microbiota. Meta-analysis was conducted to evaluate the summary relative risk (RR) and 95% confidence intervals (CIs) of combined studies. RESULTS: Our findings revealed that the internal NH(3) and/or H(2)S were negatively related to the Lactobacillus, which is beneficial to male fertility, whereas NH(3) and H(2)S were positively related to Bacteroides, which showed negative effects on male fertility. The meta-analysis comparing Lactobacillus and Bacteroides levels with NH(3) showed statistically significant results (p<0.001). CONCLUSIONS: The meta-analysis is the first to confirm these facts and explored the potential existence of a gut microbiota-inner gases-male fertility axis in the human gut.