Age-related changes, influencing factors and crosstalk between vaginal and gut microbiota: a cross-sectional comparative study of pre- and postmenopausal women

Objective The ideal vaginal environment is maintained by Lactobacillus species, which keep the vagina clean and free of infections, including sexually transmitted diseases and human papilloma virus infection. Other reported health benefits of Lactobacillus include a favorable impact on fertility and immunity, leading to a reduced risk of gynecological malignancies. Age-related decline in estrogen affects the population of Lactobacillus , leading to dominance of pathogenic flora and increased diversity in vaginal microbiota. In this study, we compared the differences between the vaginal microbiota of premenopausal and postmenopausal women. In addition, we examined the relationships between vaginal and gut microbiota, as well as their relationships to sex hormones and equol producing ability. Methods This was a cross-sectional study of 35 premenopausal and 35 postmenopausal women, ranging from 27 to 76 years of age. We compared parameters such as the composition of the gut and vaginal microbiota, vaginal pH, sex hormones in the blood (estradiol and follicular stimulating hormone), and urinary equol concentration. Results In the vaginal microbiota of premenopausal women, Lactobacillus species constituted approximately 71.98%, and pathogenic flora constituted approximately 16.87%. They were 10.08% and 26.78%, respectively, in the vaginal microbiota of postmenopausal women. Therefore, the proportion of Lactobacillus was significantly low, whereas microbial diversity and vaginal pH were significantly high (p<0.0001) in postmenopausal women. The compositions of the vaginal microbiota were significantly different in pre- and postmenopausal women. However, such differences were not noticeable in the gut microbiota. Urinary equol production had no significant correlation with vaginal microbiota, although it had significant relationships with gut microbiota in postmenopausal women. There were significant correlations among bacterial species in the gut and vaginal microbiota, especially in postmenopausal women. In both groups, the proportions of vaginal Lactobacillus were inversely correlated with vaginal microbial diversity and vaginal pH. Conclusion Postmenopausal women had significantly low Lactobacillus and high pathogenic flora in their vaginal flora, whereas such age-related differences were not identified in gut microbiota. There were significant correlations among the bacterial species inhabiting the gut and vaginal microbiota, especially in postmenopausal women, indicating potential crosstalk between each other.