Dr. Rong Li of Peking University Third Hospital led a study showing bacterial postbiotics can improve endometrial health and fertility in women over 35. Researchers published the study in the journal Cell Host & Microbe on August 6, 2026. Their findings suggest that treating mice and humans with bacterial supplements or derived postbiotics enhances uterine receptivity for pregnancy.
Traditionally, medical professionals have attributed reproductive aging primarily to declining ovarian reserves and lower embryo quality. However, Li explained that a successful pregnancy also requires a healthy and receptive endometrium. The endometrium serves as the inner lining of the uterus where a fertilized egg implants during pregnancy.
As women age, changes occur within the uterine environment, including a reduction in beneficial bacteria. This decline can make conception more difficult through both natural means and in vitro fertilization.
Bacterial Species and Age Groups
To understand these microbial changes, Li's research team analyzed endometrial samples from 149 women aged 20 to 45 who were undergoing infertility treatment. The researchers divided the participants into three age categories: under 30 years old, 30 to 35 years old, and over 35 years old.
Younger patients displayed a significantly higher abundance of Lactobacillus bacteria in their endometrial tissue compared to the two older groups. In particular, levels of the species Lactobacillus gasseri decreased as patient age increased.
Li noted that overall microbial diversity did not change notably across the different age groups. Instead, the primary differences between the groups involved specific bacterial species rather than overall diversity.
One year after the initial sampling, researchers conducted a follow-up with the study participants. A total of 93 women had undergone embryo transfers, which resulted in 56 clinical pregnancies.
Endometrial Health and Embryo Implantation
While pregnancy rates did not differ significantly among the three age groups, pregnant participants exhibited a higher abundance of Lactobacillus in their endometrium than those who did not become pregnant.
Further laboratory tests evaluated five distinct Lactobacillus strains found in the samples. Among these strains, L. gasseri provided the strongest support for endometrial health by demonstrating antioxidant and anti-inflammatory properties alongside the highest rate of adhesion to endometrial cells.
The team then examined human endometrial stromal cells, which are connective tissue cells within the uterus. They discovered that a specific component of L. gasseri known as exopolysaccharides helps protect against endometrial aging.
In animal testing, older mice treated with exopolysaccharides derived from L. gasseri achieved higher rates of embryo implantation than untreated mice. Li stated that using a defined bacterial product rather than a live microorganism could offer more viable options for clinical treatment.
Clinical Potential and Safety Warnings
These findings indicate that the uterus may represent an easier target for postbiotic therapies than eggs or embryos. However, Li cautioned women against self-medicating with over-the-counter L. gasseri products, emphasizing that their efficacy in treating infertility remains unvalidated.
Li also stressed that additional research is required before drawing firm conclusions. She noted that this study alone does not prove that uterine microbiome changes directly cause endometrial aging or poor pregnancy outcomes.
Describing female reproductive aging as a multidimensional process, Li said endometrial health and local microbiota deserve greater attention from medical researchers. Although the research remains in an early phase, she expressed excitement about its potential to enhance female fertility.
