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Article by: Katherine Lawless

Case study: Lactose intolerance related bacteria abundant in women with PCOS


What is polycystic ovary syndrome?

Polycystic ovary syndrome (PCOS) is a hormone disorder common among women during reproductive age. PCOS can cause the ovaries to develop numerous small collections of fluid (follicles) and fail to regularly release egg cells. Women with PCOS are likely to have irregular or prolonged menstrual periods or excess male hormone (androgen) levels.[1]

According to the Mayo Clinic, the exact cause of PCOS is not known. PCOS can be associated with obesity, increasing the risk of long-term complications such as type 2 diabetes and heart disease.[1]

Worldwide, 6-18% of women are diagnosed with PCOS. In India, PCOS affects the life of about 6.5 to 19.4 million women from ages 14 to 25, and parallels the obesity epidemic.[2]

“In the 1930-s, PCOS was defined as a gynaecological disorder, however, it is associated with a constellation of metabolic conditions, such as obesity, dyslipidaemia, metabolic syndrome, endothelial dysfunction, inflammation, insulin resistance, hypertension and other cardiovascular risks.“[2]

PCOS and its connection to the gut microbiome

The link between the gut microbiome and conditions such as obesity and inflammatory response have been studied by many researchers over the past decade. So, it wouldn’t be a surprise that PCOS (that is associated with conditions like obesity and inflammation) would also share a connection to the gut microbiome.

Dr. Saqib Hassan and colleagues from Imperial College London explored this connection further by collecting gut microbiome samples (using OMNIgene·GUT) from 20 women ages 16-25 in Kashmir, India who have PCOS and they recently published their findings; Bifidobacterium is enriched in gut microbiome of Kasmiri women with polycystic ovary syndrome.

They performed a metagenomic DNA extraction and 16S rRNA sequencing on the fecal samples and found 7 genera and 3 family level groups that were significantly enriched in the women with PCOS, including enrichment at both levels in Bifidobacterium and Bifidobacteriaceae. For the first time they identified a significant direct association between butyrate producing Eubacterium and follicle-stimulating hormone levels. Further analysis of Eubacterium indicated that it was associated with weight. Regarding enrichment of species, overall they found a significant increase in relative abundance of Bifidobacterium.

Bifidobacterium and polycystic ovary syndrome

What is Bifidobacterium? It is a genera of bacteria that mainly resides in the human gut. They are associated to have good nutritional values as Bifidobacterium are known to produce thiamine, riboflavin, vitamin B6, and vitamin K.[3] Members of the genera have been used extensively as probiotics in promoting human health and are generally regarded as safe. [4]

“Relative Bifidobacterium abundance in human gut is known to be driven by lactose intolerance. In lactose-intolerant individuals, lactose is not metabolized in the small intestine and proceeds to the colon where it is fermented by members of the gut microbiome; this fermentation leads to gas production, a major symptom associated with lactose intolerance. Thus, genetic variants that reduce lactase activity can promote the growth of lactose fermenting bacteria in the colon, but only if the individual consumes dairy products.[2]"

Bifidobacterium abundance in the gut is known to have favourable metabolic outcomes however, according to Hassan et al., a recent report also showed that not all strains of Bifidobacterium are functional and these strain level differences can only be resolved by shotgun metagenomic sequencing.

Interested in learning more about shotgun metagenomic sequencing for your microbiome study? Email us at or click here for more information regarding our sister company, Diversigen, and their microbiome lab services.

So what does lactose intolerance have to do with PCOS?

That is currently the mystery. According to Hassan et al, there might be a possible association between adult type hypolactasia (lactase deficiency that is caused by an injury to the small intestine) and PCOS, but it is not certain and needs to be explored. Hassan et al. also found many other species involved in lactic acid fermentation, such as Alkalibacteroim and Megashaera that are enriched in the gut of women with PCOS.

Since most of these bacteria are known to provide beneficial effects, Hassan et al. found it difficult to conclude with certainty if these lactose intolerance bacteria are the cause or consequence of the metabolic disturbances seen in PCOS or if these bacteria are specific to Indian women. What is clear, however, is that there is an association with PCOS and the gut microbiome warranting further investigations.

Interested in collecting stool samples for your own study? Send us an email at for more information.

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[2] Hassan S et al. Bifidobacterium is enriched in gut microbiome of Kashmiri women with polycystic ovary syndrome. bioRix 718510 (2019).

[3] McCartney AL. Bifidobacteria in Foods. Encyclopedia of Food Sciences and Nutrition. 2003.

[4] Abratt VR. Oxalate-Degrading Bacteria of the Human Gut as Probiotics in the Management of Kidney Stone Disease. Advances in Applied Microbiology. 2010

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