Estrogen is not a female-only hormone. Men produce estradiol, the primary biologically active form of estrogen, primarily through peripheral conversion of testosterone by the enzyme aromatase. Normal male estradiol levels run approximately 10-40 pg/mL, compared to 30-400 pg/mL in premenopausal women at different cycle phases. Men need estrogen for bone density, cardiovascular health, libido, and normal erectile function. Both deficiency and excess cause problems, and the clinical management of estrogen in men on testosterone replacement therapy is an area of ongoing debate.

How Men Make Estrogen

Aromatase (also called CYP19A1) is an enzyme expressed in adipose tissue, the testes, brain, liver, and muscle. It converts testosterone and androstenedione into estradiol and estrone. In men, approximately 80% of circulating estradiol comes from peripheral aromatization in fat tissue; the remaining 20% is secreted directly from the testes.

The amount of estrogen a man produces is directly influenced by:

  • Testosterone levels: More substrate for aromatase means more conversion
  • Body fat percentage: Adipose tissue contains the most aromatase; higher body fat increases conversion
  • Genetic aromatase activity: Variation in the CYP19A1 gene affects aromatase efficiency
  • Age: Aromatase activity increases with age, contributing to the rise in estradiol relative to testosterone seen in older men

Normal Estradiol in Men and What It Does

The reference range for male estradiol varies by laboratory and assay method, but 10-40 pg/mL (35-150 pmol/L) represents a common clinical target range. Assay method matters significantly: immunoassay-based estradiol tests (the standard lab panel) are less accurate at low levels in men than liquid chromatography-mass spectrometry (LC-MS). For men with symptoms of estrogen imbalance, requesting an LC-MS estradiol assay provides more reliable results.

Bone health: Estrogen is the primary driver of bone mineral density maintenance in men as well as women. Men with estrogen deficiency, from aromatase inhibitor treatment or rare cases of aromatase enzyme deficiency, develop severe osteoporosis. A landmark case report in the NEJM of a man with an inactivating mutation in the aromatase gene (no estrogen production) had profound osteoporosis despite normal testosterone levels, and his bone density improved only after estrogen replacement.

Libido and erectile function: Estrogen contributes to libido in men. Men with very low estradiol (below 10-15 pg/mL) report reduced sexual interest comparable to testosterone deficiency. Estrogen also maintains the function of the corpus cavernosum, reducing it excessively impairs erectile function.

Cardiovascular health: Estradiol has vasodilatory and anti-inflammatory effects in blood vessels. Very low estradiol in men is associated with increased cardiovascular risk. This is one reason aggressive suppression of estrogen in men on TRT is clinically controversial.

Elevated Estrogen in Men: When Is It a Problem?

Elevated estradiol in men causes:

  • Gynecomastia: Breast gland tissue growth, distinct from lipomastia (fatty tissue). Occurs when the estradiol-to-testosterone ratio increases significantly, either from rising estrogen or falling testosterone.
  • Water retention: Estrogen promotes sodium and water retention, contributing to soft tissue edema
  • Reduced libido: High estrogen suppresses GnRH and thus testosterone production, a negative feedback effect
  • Mood changes: Some men report irritability or emotional changes at elevated estradiol levels

Elevated estradiol in obese men without testosterone replacement typically reflects high aromatase activity from excess adipose tissue. Weight loss lowers estradiol by reducing aromatase-producing fat.

Estrogen Management on TRT

When a man begins testosterone replacement therapy, testosterone levels rise and so does aromatization, more testosterone substrate means more estradiol production. Some prescribers routinely add anastrozole (an aromatase inhibitor) to TRT protocols to prevent estradiol elevation.

Whether this is appropriate depends on actual estradiol levels and symptoms. Routine use of aromatase inhibitors without evidence of elevated estradiol or estrogen-excess symptoms is not supported by evidence and can drive estradiol below the range needed for bone and cardiovascular health. The Endocrine Society guidelines do not recommend routine aromatase inhibitor use with TRT.

The appropriate use is targeted: in men who develop symptomatic gynecomastia or consistently elevated estradiol (above 50-60 pg/mL on LC-MS) with associated symptoms, low-dose anastrozole may be appropriate after discussion of risks.

Anastrozole Side Effects and Risks

Anastrozole and similar aromatase inhibitors (letrozole, exemestane) used in TRT settings carry specific risks:

  • Bone loss: Reduced estrogen directly impairs bone maintenance
  • Lipid changes: Estrogen has favorable effects on HDL; suppressing it can worsen lipid profiles
  • Joint pain: A common side effect of aromatase inhibitors at any dose
  • Mood effects: Some men report worsening mood and anxiety with estrogen suppression

Given these risks, indiscriminate anastrozole use in TRT should be scrutinized. The goal is estradiol within a healthy male range, not estradiol suppressed to the minimum.

For more on TRT broadly, see TRT Side Effects: What the Research Actually Shows. For the delivery method that most affects estradiol levels (through peak testosterone), see Testosterone Injections vs. Gel: Which Delivery Method Is Better?.