Hormones and the cycle

Oestrogen

Also called: estrogen, estradiol, oestradiol

Oestrogen is the main female sex hormone, produced mostly by the ovaries before menopause. It builds the uterine lining in the first half of the cycle, supports bone density, modulates mood, and shapes the gut microbiome. Levels rise and fall through the cycle, drop dramatically through perimenopause, and stay low after menopause. Many gut and metabolic changes in midlife trace back to falling oestrogen.

Forms of oestrogen

  • Estradiol (E2): the most potent and most studied. Dominant form in pre-menopausal women.
  • Estrone (E1): less potent, dominant after menopause.
  • Estriol (E3): produced mainly in pregnancy.
  • All convert into each other through metabolism.

What it does

  • Builds the uterine lining each cycle.
  • Supports bone density (its loss in menopause drives osteoporosis risk).
  • Maintains skin collagen and hydration.
  • Influences mood through serotonin and dopamine pathways.
  • Shapes the gut microbiome (the estrobolome), with bacteria that metabolise oestrogen and influence circulating levels.
  • Modulates insulin sensitivity and fat distribution.
  • Cardio-protective in pre-menopausal women (one reason CV disease rises sharply post-menopause).

How it changes through life

  • Puberty: sharp rise.
  • Reproductive years: cyclic, peaks twice per cycle (mid-follicular and mid-luteal).
  • Pregnancy: rises 30-fold.
  • Perimenopause (4 to 10 years pre-menopause): erratic, with peaks and crashes.
  • Menopause: drops 90 percent.
  • Post-menopause: low and stable, mostly from adipose conversion of androgens.

How it affects the gut

Oestrogen receptors are widespread in the gut. Adequate oestrogen supports gut barrier function, maintains microbiome diversity, and dampens visceral sensitivity. Falling oestrogen in perimenopause and menopause shifts the microbiome composition, slows gastric emptying, and increases gut sensitivity to food and stress. This is why many women develop new IBS-like symptoms in their 40s and 50s.

Symptoms of low oestrogen

  • Hot flushes and night sweats.
  • Vaginal dryness and discomfort during sex.
  • Sleep disruption.
  • Mood changes, including new anxiety or depression.
  • Joint pain.
  • Dry skin and brittle hair.
  • New gut symptoms (bloating, constipation, food sensitivity).
  • Weight redistribution to the middle.
  • Bone density loss (silent until measured).

On HRT

Hormone replacement therapy with oestrogen (plus progesterone in women with a uterus) is now the standard of care for menopausal symptoms in women without contraindications. Topical/transdermal oestrogen (patches, gels, sprays) is preferred over oral because it bypasses the liver and reduces clot risk. The picture is much more positive than the early 2000s WHI trial concluded; modern guidance balances benefits (symptoms, bone, possibly cardiovascular) against small risks (breast cancer, clots) on an individual basis.

Common questions

Should I get my oestrogen tested?
Less useful than you might think. Levels vary day-to-day, especially in perimenopause. Diagnosis of perimenopause and menopause is mostly based on symptoms plus age. The exception is suspected premature menopause (under 40) where blood tests matter.
Does the gut microbiome affect my oestrogen?
Yes. The estrobolome, bacteria that produce beta-glucuronidase, affects how much oestrogen circulates vs gets excreted. Low diversity gut microbiomes can reduce circulating oestrogen, contributing to symptoms even pre-menopause.
Can diet affect oestrogen levels?
Modestly. Phytoestrogens in soy, flax, lentils, and chickpeas have weak oestrogen-like effects. Will not replace HRT but can soften symptoms for some. High alcohol raises oestrogen short-term; chronic heavy drinking lowers it long-term. Body fat percentage influences post-menopausal oestrogen via adipose conversion.
Is oestrogen safe for everyone?
Most pre- and post-menopausal women can use HRT safely. Contraindications include personal history of oestrogen-sensitive cancer, recent blood clots or stroke, severe liver disease, and some specific genetic risks. Discuss with a GP or menopause specialist.

Sources