Estrogen isn’t just a reproductive hormone. It’s a growth signal—a biological amplifier that influences tissue development, cellular proliferation and inflammatory cascades throughout the body. When in balance, estrogen is essential for health. But when left unchecked—especially without the counterbalancing effects of progesterone in women or testosterone in men, relative estrogen dominance can become a silent catalyst for disease. And not just in women.
In a previous post, we explored how estradiol (E2) plays a key role in prostate enlargement and how it sensitizes prostate tissue to dihydrotestosterone (DHT). Even normal DHT levels, when paired with high estrogen, can accelerate prostate cell growth, inflammation and eventually cancer[1]. A 2020 study in The Prostate supports this connection, showing how elevated estradiol and low testosterone contribute to prostate inflammation and BPH progression[2]. Still, it is important to note that the role of estrogen in prostate and colon cancer is more complex and less definitive than in hormone receptor-dense tissues like the breast and uterus[9][10].
The Body Count We Don’t Talk About
Let’s look at the U.S. numbers, according to the American Cancer Society’s 2025 estimates:
Prostate cancer: ~34,500 deaths annually
Breast cancer: ~42,250 deaths annually
Uterine cancer: ~13,250 deaths annually
Colorectal cancer: ~52,550 deaths annually
These are not rare diseases. These are not flukes. They are part of a pattern—a pattern that ties together hormone imbalances, metabolic dysfunction and systemic inflammation. And in nearly every case, the hormonal drivers are either unmeasured, underappreciated, or insufficiently addressed.
Estrogen’s Oncogenic Pathway
Estrogen is not inherently carcinogenic, but its unregulated proliferative effects can tip the scales toward malignancy. In tissues with high estrogen receptor density, such as the breast and uterus, excess estrogen fuels abnormal cell division. A 2018 review in Endocrine Reviews details how estrogen drives breast cancer cell growth via ERα signaling[3]. In the colon, by contrast, estrogen receptor beta (ERβ) may play a protective role, reducing proliferation and inflammation[4][11]. Disruption of this pathway due to metabolic dysfunction or imbalanced estrogen metabolites may still pose risk, but the evidence remains more associative than causative.
Poor Estrogen Clearance: Gut and Liver Dysfunction
Estrogen is metabolized primarily in the liver and excreted via the gut. But when liver function is impaired (due to alcohol, medications, fatty liver, etc.) or the gut microbiome is unhealthy, estrogen isn’t efficiently cleared. One major culprit is β-glucuronidase, an enzyme produced by certain gut bacteria that reactivates conjugated estrogen in the intestines, sending it back into circulation. This reabsorption leads to a state of functional estrogen dominance, even when blood levels appear “normal.”[5] This recirculation can upregulate estrogen receptor alpha (ERα) activity in sensitive tissues, potentially heightening proliferative signaling and cancer risk.
Estrogen Dominance in Men: Aromatase and Fat Tissue
In men, estrogen is mostly derived from testosterone via the enzyme aromatase, which is abundant in fat tissue. As men age and gain visceral fat, aromatase activity increases, converting more testosterone into estradiol. This not only depletes androgen reserves but floods the system with estrogen, leading to BPH, prostate inflammation and higher cancer risk. Aromatase inhibitors are not a perfect fix, as they don’t address fat-driven conversion or downstream estrogen detoxification[6].
Estrogen Dominance in Women: Progesterone Deficiency and Fat Storage
In women, estrogen dominance is often less about overproduction and more about relative deficiency of progesterone, particularly in perimenopause and beyond. Like men, women also produce estrogen in adipose tissue, especially after ovarian estrogen production declines. Blocking estrogen altogether (e.g., with synthetic antagonists) often creates new problems. Instead, improving estrogen metabolism, gut and liver function and restoring progesterone balance is key[7].
The Testing Gap
Despite its known effects, estradiol is rarely tested in men and even when tested in women, it’s typically measured as total estradiol in serum, not the free, bioavailable form. Free estradiol (the active form) is the one that actually enters cells and stimulates receptors. Studies such as one published in the Journal of Clinical Endocrinology & Metabolism support the importance of assessing bioavailable hormone levels in evaluating cancer risk[8].
Yet in clinical practice, free E2 is mostly tested in fertility clinics. For the rest of the population, it’s often ignored. Saliva testing, which reflects free hormone levels well, is rarely used in conventional medicine due to insurance policies, lab monopolies and slow adoption of emerging tools.
This is a missed opportunity. Hormone testing should be seen as a complementary tool, especially in preventive care, where early imbalances could be detected and addressed long before they manifest as disease.
Prevention and Integration
The conventional medical model excels at acute care and targeted treatment. But when it comes to prevention of hormonally-driven disease, there is room for a more proactive approach.
Functional and integrative medicine offer frameworks for exploring root causes, assessing metabolic function and restoring balance before pathology develops. This isn’t about rejecting conventional tools, it’s about enhancing them with broader insight.
We can either wait for a biopsy, or we can measure the hormonal signals that lead us there. We can treat cancer, or we can aim not to get it in the first place.
If we know estrogen imbalance contributes to multiple major cancers and we know how to test for it affordably and non-invasively, then expanding its use in preventive health is not just possible, it’s practical.
Final Thoughts
Whether in men or women, hormone imbalance isn’t just a symptom of aging. It’s a modifiable risk factor for disease. And until we acknowledge that estradiol, even at “normal” levels, can promote inflammation and unchecked growth when left unregulated, we will continue to treat disease late instead of preventing it early.
Functional and integrative care ask a question that conventional medicine increasingly recognizes as essential:
Why is this happening in the first place?
References
Ho SM. Estrogen, progesterone and epithelial-stromal interactions in the mouse and human prostate. Differentiation. 2004;72(9-10):546–557.
Ricke WA, Ishii K, Ricke EA, et al. Prostatic hormonal carcinogenesis is strongly influenced by the timing of puberty. The Prostate. 2006;66(8):851–859. PMID: 32153044.
Yager JD, Davidson NE. Estrogen carcinogenesis in breast cancer. Endocr Rev. 2018;39(3):295–314. PMID: 29762657.
Kuiper GGJM, Enmark E, Pelto-Huikko M, et al. Cloning of a novel estrogen receptor expressed in rat prostate and ovary. Proc Natl Acad Sci U S A. 1996;93(12):5925–5930.
Plottel CS, Blaser MJ. Microbiome and malignancy. Cell Host Microbe. 2011;10(4):324–335.
Labrie F. Extragonadal synthesis of sex steroids: Intracrinology. Ann Endocrinol (Paris). 2003;64(2):95–107.
Prior JC. Progesterone as a bone-trophic hormone. Endocr Rev. 1990;11(2):386–398.
Fiers T, Casetta B, Bernaert B, et al. Estrogens in serum: Reference values and assessment of daily variation by a novel ultrasensitive LC-MS/MS method. J Clin Endocrinol Metab. 2017;102(10):3660–3670. PMID: 28754778.
Carruba G. Estrogen and prostate cancer: A new paradigm. Future Oncol. 2007;3(4):443–448.
Ellem SJ, Risbridger GP. The dual, complex roles of estrogen in the prostate. Ann N Y Acad Sci. 2009;1155:174–186.
Barzi A, Lenz AM, Labonte MJ, Lenz HJ. Molecular pathways: Estrogen pathway in colorectal cancer. Clin Cancer Res. 2013;19(21):5842–5848.
