Gut bacteria link to PCOS fertility problems, study finds

Lower levels of a gut microbe may help explain why women with polycystic ovary syndrome (PCOS) experience fertility issues.

New findings suggest that women with PCOS have around half the amount of a gut bacterium called Parabacteroides merdae compared to those without the condition.

PCOS is the most common hormonal condition in women of reproductive age and a leading cause of infertility, yet its causes and treatments remain poorly understood.

The condition can cause irregular or missed periods, weight gain, excessive hair growth, and increases the risk of type 2 diabetes, high blood pressure, heart problems and endometrial cancer.

In the study, 220 women under the age of 35 from 44 cities in China were monitored, half of whom had PCOS. All participants provided blood, stool and uterine lining samples.

Although both groups had similar pregnancy rates, women with PCOS were twice as likely to experience complications including miscarriage, preterm birth and gestational diabetes.

Researchers found that P. merdae plays a key role in converting isoleucine – an amino acid present in the gut – into short-chain fatty acids, which support reproductive health. Women with PCOS had higher levels of isoleucine in their blood and uterus, likely due to a lack of the bacteria needed to process it.

When scientists added extra isoleucine to uterine cells in the lab, the cells showed signs of premature ageing and stopped working properly.

This suggests that low levels of P. merdae could impair fertility by allowing isoleucine to accumulate and damage reproductive cells.

However, some doctors remain sceptical. Andrea Dunaif, from the Icahn School of Medicine at Mount Sinai in New York, told New Scientist that her research suggests fertility in women with PCOS often improves in their 30s – which would contradict the cell ageing theory proposed by this study.

Nonetheless, the findings may open up new avenues for treatment.

Dunaif said: “The microbiome is something [where] you could intervene with different probiotics to alter the [bacteria].

“So that is nice to have a potential target to treat because we don’t really have any specific treatments for PCOS.”