The Relationship of the Intestinal Microbiome and the Menstrual Cycle

The Relationship of the Intestinal Microbiome and the Dynamic Changes of Sex Hormone Concentrations in Women at Childbearing Age

In the present study the dynamic changes of the intestinal microbiome are observed over a 4-week period in the different stages of the menstrual cycle in women at childbearing age. The focus is on how the dynamic changes of sex hormones during a menstrual cycle of women at childbearing age (with or without contraception) are related to microbiological colonization of the gut. In Addition the Expression of the β-glucuronidase by the bacteria will be investigated.

Our gut has a complex and diverse bacterial population which is called the microbiome. The number of bacteria in the intestine is estimated to exceed 10^14. The composition of the microbiome is individual and changes over the lifetime of the host.

The composition of a healthy microbiome consists more than 90% of bacteria from the Bacteroidetes and Firmicutes phyla types. Nevertheless the microbiome varies even between healthy individuals and evolves over the lifetime.

Most of the microorganisms are not pathogen, thus they have been shown to interact with several physiological processes in our body. In Addition it has been shown that the bacterial population has an impact on building our gut epithelial cells, our immunology and the defence against pathogens.

Interestingly estrogen and the microbiome seem to be under reciprocal influence. In our body estrogen is only active in the deconjugated form. Therefore, after it was conjugated in the liver, the bacteria in the gut can perform a deconjugation through the secretion of the enzyme ß-glucuronidase. Ultimately, the activated estrogen is going back into blood circulation, otherwise it would leave the body through bile excretion. The composition of the microbiome is fundamental, because the presence and abundance of different gene expressions varies between the different types of bacteria. The bacterial genes which are responsible for metabolizing estrogens are called the estrobolome. However, data whether there is a relationship of the changes of the sex hormones during the menstrual cycle and the intestinal microbiome in women is sparse.

Parts of the estrogens circulating in the body are metabolised in the liver and are then secreted to the intestine conjugated with glucuronide. The intestinal microbiota could potentially affect estrogen metabolism via Beta-glucuronidase activity. Beta-glucuronidase is an enzyme that catalyses the deconjugation of estrogen. As a consequence, it may bind to estrogen receptors and unfold its downstream effects.

Inclusion Criteria:

• women at childbearing age
• age 18-40 years
• BMI 18.5-24.9 kg/m²
• taking oral contraceptives
• not having any contraceptives

Exclusion Criteria:

• chronic and acute infectious diseases
• history of taking antibiotics or probiotics in the last 3 months
• gastrointestinal disorders in the last 3 months
• Polycystic Ovary Syndrome
• disorders of the menstrual cycle (e.g. oligomenorrhea, anovulation)
• other than mediterranean diet