Fibroids And Hormones: A Plain English Explanation Of What Is Actually Happening

The hormonal picture of fibroids can feel overwhelming — estrogen dominance, IGF-1, progesterone, cortisol. This article explains the key relationships in plain language so you can understand what is driving your symptoms and what interventions are addressing what.

The Primary Driver: Estrogen

Fibroids express estrogen receptors at much higher levels than normal uterine tissue. When estrogen binds to these receptors, it switches on genes that make fibroid cells grow and divide, and switches off genes that would normally trigger cell death. This is why fibroids grow during reproductive years when estrogen is high, and why they typically shrink after menopause when estrogen falls.

Estrogen does not have to be pathologically high to drive fibroid growth — it just has to be adequate. The hormone environment that matters most is the ratio of estrogen to progesterone, not the absolute estrogen level alone.

The Counterbalance: Progesterone

Progesterone is produced primarily in the second half of the menstrual cycle (luteal phase) after ovulation. In a healthy cycle, progesterone rises significantly to counterbalance estrogen’s proliferative effects on the endometrium. When this balance is disrupted — when ovulation does not occur, or when progesterone production is impaired — estrogen acts more unopposed. This state is often called “estrogen dominance” — not necessarily because estrogen is too high, but because the progesterone counterbalance is insufficient. For a deeper dive, see our article on fibroids and estrogen dominance.

The Stress Hormone: Cortisol

Cortisol is the adrenal stress hormone. Under chronic stress, cortisol is produced at the expense of progesterone — both use the same hormonal building blocks, and under stress, cortisol wins. Higher cortisol therefore means lower progesterone, worsening estrogen dominance. This is why stress management is a genuine fibroid management tool, not just a lifestyle suggestion.

The Growth Signal: IGF-1

Insulin-like growth factor 1 (IGF-1) is produced in response to insulin — which rises after eating sugar and refined carbohydrates. IGF-1 directly signals fibroid cells to grow and divide. This is why reducing refined carbohydrates and sugar is specifically relevant to fibroids, not just general health. The dietary changes that stabilise blood sugar are directly reducing this growth signal.

Putting It Together

Fibroids grow in: high estrogen + insufficient progesterone (estrogen dominance) + elevated cortisol (suppressing progesterone) + elevated IGF-1 (from sugar/refined carbs). Every effective natural intervention addresses one or more of these factors. Diet reduces estrogen load and IGF-1. Exercise reduces body fat (peripheral estrogen) and cortisol. Stress management reduces cortisol and restores progesterone balance. This is not complicated once you see the connections. The natural treatment plan is built on exactly this framework.