How does your gut microbiome influence your hormone balance?
Your gut microbiome drives multiple hormones through enzymes, fermentation products and bile acids, ranging from oestrogen to thyroid hormones and satiety hormones. The evidence is compelling enough to take your gut flora seriously, but too preliminary for specific treatment recommendations beyond improving dietary fibre intake and diversity.
Gut bacteria produce an enzyme that converts oestrogen from an inactive to an active form. When the diversity of your gut flora declines, so does this enzyme, and with it your active oestrogen level. Researchers link this to conditions such as metabolic syndrome, endometriosis and PCOS. The connection is biologically well explained and is supported by several studies, although the direction of cause and effect in humans has not yet been fully established.
Bacteria that ferment fibre produce short-chain fatty acids. These substances stimulate specialised cells in the gut wall to produce satiety hormones. Two hormones play a major role here: GLP-1, which also regulates blood sugar levels, and PYY, which suppresses the sensation of hunger. Disruptions in this system are associated with obesity and diabetes. Interestingly, metformin, a widely used diabetes drug, also works in part through this microbiome-hormone channel, although the exact contribution of the gut flora to that process has not yet been precisely defined.
Your thyroid gland also has a connection to your gut microbiome. Dysbiosis disrupts the absorption of nutrients the thyroid needs, such as iodine, selenium and zinc. This can impair the production and conversion of thyroid hormones. Dysbiosis is also linked to autoimmune diseases of the thyroid, such as Hashimoto's. Probiotics showed a positive effect on thyroid hormones in several studies, but these are still small-scale investigations.
Through the so-called gut-brain axis, gut bacteria also influence neurotransmitters and the hormone balance that regulates your mood. Dysbiosis is associated with an increased risk of depression. The precise cause-and-effect relationship here remains unclear, however: it has not yet been established whether a disrupted gut flora causes depression, whether depression disrupts the gut flora, or whether both occur simultaneously. Targeted treatments therefore do not yet exist.
A recent study (published in Science) revealed an interesting chain of events in osteoarthritis. Patients with osteoarthritis had lower levels of a particular gut bacterium, resulting in reduced production of a bile acid compound that normally stimulates GLP-1 release. Lower GLP-1 in the joint appears to worsen joint inflammation. In mice, restoring this compound had a protective effect. In humans, only associational data exist; it is too early to draw clinical conclusions from this.
All claims are based on PMID 28778332, 32545596, 39125376, 40037297, 39713871, 40179178, 35017199, 30874963. Most of the evidence is associational or comes from animal models; randomised research in humans across this broad field is scarce.
How do your hormone levels change throughout your menstrual cycle?
Your hormone levels follow a recognisable pattern throughout the cycle: oestrogen and progesterone rise and fall at set moments, with a sharp LH peak around ovulation. Bear in mind that there are large differences between women, and that the pill largely suppresses this pattern.
Does the amount of muscle mass you have affect your hormone balance?
More muscle mass improves your insulin sensitivity and is associated with more favourable hormone values after training, but the strongest causal relationship runs from hormones to muscle, not the other way around. If you have concerns about your hormone balance, discuss them with your doctor.
What does pregnancy do to your hormone balance in the long term?
Pregnancy brings about hormonal changes that are partly temporary, but in the case of gestational diabetes the risk of type 2 diabetes may remain permanently elevated. If you have had this, have your blood sugar checked afterwards.
What are normal hormone levels for women, and how do you get them tested?
There is no universal standard for hormone levels in women: they depend on age, cycle phase, and measurement method. Always have testing guided by a doctor who takes that context into account, especially for testosterone.
Can a vitamin D deficiency affect your hormones?
A vitamin D deficiency disrupts hormone levels, primarily through a rise in parathyroid hormone PTH, which affects your bones, muscles, and possibly your heart. The effect on sex hormones such as testosterone appears limited, but this has been too little studied to allow firm conclusions.
How do you get your hormone levels tested during perimenopause?
Hormone tests during perimenopause are difficult to interpret: AMH is the most practical option, but does not reliably predict your fertility. Always have results interpreted with the guidance of a doctor.