Estrogen in men: Low Estradiol can ruin your TRT therapy

Low estradiol in men is common, especially on testosterone therapy, and can quietly drain libido, mood, and bone strength. Here is how to recognize low estradiol, get the right tests, and correct it without crashing your hormones.

The relationship

Estradiol is the main form of estrogen in adults. In men, most estradiol is made by converting testosterone into estradiol through an enzyme called aromatase, which sits in fat tissue, muscle, and the brain. That means estradiol levels in men depend heavily on both testosterone levels and body composition.

For years, clinics treated estradiol as something to be suppressed in male hormone care. Men on testosterone replacement therapy, or TRT, were often given aromatase inhibitors such as anastrozole to keep estradiol “low” even when they had no symptoms or abnormal labs. Large human studies now show that low estradiol in men can impair sexual function, mood, and body composition even if testosterone is in a normal or high range.^[1]

In one carefully controlled study from Massachusetts General Hospital, researchers chemically suppressed estradiol in healthy men while holding testosterone steady. Men developed more body fat, decreased sexual desire, and more erectile problems when estradiol dropped below about 20 pg/mL, confirming that estradiol is essential for male sexual health and fat regulation.^[1] Other research links estradiol below roughly 20 pg/mL to higher fracture risk and lower bone mineral density in men.^[2]

How it works

To understand low estradiol in men, it helps to see how testosterone, aromatase, and estradiol work together across the body.

Testosterone as the raw material

Testosterone is the primary male sex hormone, produced mainly in the testes. Estradiol in men is made locally in tissues when aromatase converts testosterone into estradiol. When total testosterone falls below about 350 ng/dL, or free testosterone falls below about 100 pg/mL, both androgen actions and estradiol production usually decline.^[3]

Because most estradiol in men comes from this conversion, any cause of low testosterone — aging, testicular damage, pituitary disease, or medications — can lead to low estradiol in men as well.^[3]

Aromatase and body fat

Aromatase is an enzyme that turns testosterone into estradiol. It is found in fat tissue, liver, brain, and muscle. Because fat cells carry a lot of aromatase, men with higher body fat often convert more testosterone to estradiol and can have higher estradiol levels, while very lean men may produce less estradiol from the same testosterone level.^[4]

This balance matters on TRT. An overweight man given a high testosterone dose may drive estradiol too high. A lean man given a moderate testosterone dose, plus an aromatase inhibitor, may crash estradiol into the low range and feel worse, even if target testosterone levels are reached.^[4]

Estradiol and the brain

Estradiol acts directly in the brain on receptors involved in mood, motivation, and sexual desire. Human studies show that suppressing estradiol in men leads to lower libido, more depressive symptoms, and worse sexual satisfaction, even when testosterone remains normal.^[1],[5]

Low estradiol in men can also impair nitric oxide signaling in blood vessels, which is critical for achieving and maintaining erections. This may explain why some men on aggressive estradiol-blocking regimens notice weaker erections despite “high” testosterone labs.^[5]

Estradiol and bone, muscle, and fat

Estradiol helps maintain bone density by slowing bone breakdown cells called osteoclasts. Large studies in older men show that low estradiol is a strong predictor of fractures and low bone mineral density, sometimes more so than testosterone alone.^[2]

Estradiol also influences how the body stores fat and builds muscle. When estradiol is suppressed in men, total fat mass and belly fat increase, while lean mass may fall or fail to improve as expected during TRT.^[1]

TRT, aromatase inhibitors, and the sweet spot

Testosterone replacement therapy can raise estradiol by increasing the amount of testosterone available to be converted. Some men need help controlling very high estradiol, for example if they develop breast tenderness or fluid retention. But routine use of aromatase inhibitors without symptoms or data can push estradiol too low and undo much of the benefit of TRT.

Clinical experience and trial data suggest that many men feel and function best when estradiol stays roughly in the 20–50 pg/mL range, rather than being pushed into single digits. In practice, symptoms and trends over time matter more than chasing one “perfect” number.^[1]

Conditions linked to it

Low estradiol in men rarely appears in isolation. It often travels with other hormone or health issues that need attention.

• Male hypogonadism: Hypogonadism means the testes do not make enough testosterone. Common causes include aging, testicular injury, chemotherapy, pituitary tumors, and certain medications. Because estradiol in men comes from testosterone, hypogonadism often leads to low estradiol and related problems such as low libido, reduced bone density, and increased fat mass.^[3]
• Overuse of aromatase inhibitors: Medications like anastrozole or letrozole block aromatase. In oncology, high doses are used to treat some breast cancers. In men, low doses are sometimes prescribed with TRT. When overused or given without monitoring, they can drive estradiol into the low or undetectable range, triggering sexual, mood, and bone symptoms.
• Very low body fat or extreme dieting: Athletes, bodybuilders in contest prep, or men with chronic undernutrition may have both low testosterone and low estradiol. High training loads plus severe calorie restriction can impair the hypothalamic–pituitary–gonadal axis, the hormone system that tells the testes to make testosterone.^[6]
• Chronic illness and inflammation: Long-term illnesses such as uncontrolled diabetes, chronic liver disease, kidney failure, or inflammatory disorders can lower testosterone and estradiol together. Some chronic opiate or glucocorticoid use has a similar effect.^[7]
• Genetic or rare endocrine disorders: Very rarely, men have genetic aromatase deficiency, meaning they cannot convert testosterone to estradiol. Case reports show these men develop tall stature, open growth plates, low bone density, and metabolic issues until they receive estradiol replacement.

Evidence limitations: Many data on low estradiol in men come from observational studies or small trials, so we can see strong associations but not perfect cause-and-effect. In extreme genetic cases, the role of estradiol is clearer, but most men fall into a gray zone where symptoms, labs, and clinical judgment must be combined.

Symptoms and signals

Low estradiol in men can feel different from low testosterone, though the two often overlap. Pay attention to symptom clusters rather than a single sign.

• Sexual changes
  • Drop in sexual desire or fewer sexual thoughts
  • Difficulty getting or keeping an erection, especially when TRT labs look “good”
  • Less sensitivity or weaker orgasms
  • Decline in morning erections
• Mood and brain changes
  • Feeling emotionally flat, numb, or less motivated
  • New or worsening low mood or anxiety after starting an aromatase inhibitor
  • Higher irritability or “short fuse” without obvious triggers
  • Trouble concentrating or feeling mentally slow
• Body composition and physical changes
  • Increase in belly fat or “soft” look despite exercise
  • Slower muscle gains than expected on TRT and resistance training
  • Unexplained weight gain or difficulty leaning out
• Bone and joint signals
  • Bone fractures from minor falls or injuries
  • Loss of height or developing a stooped posture over time
  • Aches in hips, spine, or ribs without clear cause
• TRT-specific red flags
  • Feeling worse on testosterone plus an aromatase inhibitor than before therapy
  • Crash in libido or mood after an aromatase inhibitor dose change
  • Estradiol lab values repeatedly below 15–20 pg/mL with matching symptoms

These symptoms are not specific to low estradiol in men. Thyroid disorders, sleep apnea, depression, relationship stress, and other illnesses can mimic many of them. That is why targeted lab testing and a full medical evaluation are critical before making hormone changes.

What to do about it

Low estradiol in men is usually treatable once it is recognized. Here is a practical three-step plan to discuss with your clinician.

1. Step 1: Get the right testing
   • Ask for a morning blood panel including total testosterone, free testosterone, estradiol (sensitive LC/MS method if available), sex hormone–binding globulin (SHBG), and basic metabolic labs.
   • For most symptomatic men, estradiol consistently below about 20 pg/mL, especially with low libido or bone issues, deserves attention.^[1],[2]
   • If you have a history of fractures, long-term steroid use, or are over 60, a bone density scan, or DEXA, can show if low estradiol in men has already affected bone health.^[2]
   • On TRT, schedule labs 6–12 weeks after any dose change, and measure both testosterone and estradiol together.
2. Step 2: Fix the drivers with lifestyle and targeted treatment
   • Review TRT dosing: If you are on high-dose TRT with an aromatase inhibitor, your clinician can consider lowering or stopping the aromatase inhibitor first, then rechecking labs and symptoms. Many men do not need routine estradiol-blocking drugs.
   • Optimize testosterone: If testosterone is clearly low (under 350 ng/dL total or 100 pg/mL free) with symptoms, evidence supports TRT after shared decision-making. Over time, restoring testosterone often raises estradiol into a healthier range.^[3] You can review how TRT works and what to expect in this overview of testosterone replacement therapy side effects and management.
   • Address weight and sleep: Moderate fat loss, resistance training, and treating sleep apnea can improve testosterone production and overall hormone balance. This may help normalize estradiol while reducing the need for higher TRT doses.^[4],[6]
   • Support bone health: Ensure adequate calcium, vitamin D, and weight-bearing exercise. In men with significant osteoporosis and low estradiol, bone-active medications such as bisphosphonates may be considered alongside hormone management.^[2]
   • Use estradiol cautiously and rarely: Direct estradiol replacement in men is reserved for rare conditions like aromatase deficiency and should only be managed by an endocrinologist, as even small overdoses can cause breast tissue growth or other side effects.
3. Step 3: Monitor and adjust
   • Track symptoms over 3–6 months, not just lab snapshots. Use simple logs for libido, energy, sleep, and mood.
   • Recheck estradiol and testosterone at least yearly on a stable regimen, or every 3–6 months during dose changes.
   • Watch for overshooting in either direction. Signs of too-high estradiol include breast tenderness, swelling, and fluid retention. Signs of low estradiol in men are the clusters described above.

Myth vs Fact

• Myth: “Estrogen is a female hormone. Men do not need it.”
  Fact: Men need estradiol for normal sexual function, mood, and bone strength. Suppressing it too far causes real harm in studies of men.
• Myth: “On TRT, you should take an aromatase inhibitor automatically to prevent side effects.”
  Fact: Major guidelines do not recommend routine aromatase inhibitor use in all men on TRT. It is reserved for specific cases, guided by symptoms and labs.
• Myth: “Lower estradiol is always better for fat loss.”
  Fact: When estradiol is pushed too low, body fat can actually rise and muscle gains stall, even with good testosterone levels.
• Myth: “Only total testosterone matters. Estradiol is optional to measure.”
  Fact: In men with sexual, mood, or bone symptoms — especially on TRT — estradiol adds crucial information about how hormones are actually working.
• Myth: “If your estradiol level is inside the lab range, it cannot be causing symptoms.”
  Fact: Lab ranges are broad. Some men are sensitive to changes within the “normal” band, especially if estradiol drops quickly or sits at the low end for long periods.

Bottom line

Low estradiol in men is a real and often overlooked problem, especially in the era of aggressive TRT regimens and routine aromatase inhibitor prescriptions. Men need estradiol for sexual desire, erections, mood, bone strength, and healthy body composition. If you are on testosterone therapy, or have low testosterone, and your sex drive, mood, or bones are going in the wrong direction, ask your clinician to check estradiol with the same seriousness as testosterone. To better understand the bigger picture of treatment, you can also read about testosterone replacement therapy risks and testosterone therapy side effects. The goal is balance, not extremes: keeping both testosterone and estradiol in their healthy middle range so you feel and function like yourself again.

References

1. Finkelstein JS, Lee H, Burnett-Bowie SA, et al. Gonadal steroids and body composition, strength, and sexual function in men. The New England journal of medicine. 2013;369:1011-22. PMID: 24024838
2. LeBlanc ES, Nielson CM, Marshall LM, et al. The effects of serum testosterone, estradiol, and sex hormone binding globulin levels on fracture risk in older men. The Journal of clinical endocrinology and metabolism. 2009;94:3337-46. PMID: 19584177
3. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. The Journal of clinical endocrinology and metabolism. 2018;103:1715-1744. PMID: 29562364
4. Vermeulen A, Kaufman JM, Goemaere S, et al. Estradiol in elderly men. The aging male : the official journal of the International Society for the Study of the Aging Male. 2002;5:98-102. PMID: 12198740
5. Carani C, Rochira V, Faustini-Fustini M, et al. Role of oestrogen in male sexual behaviour: insights from the natural model of aromatase deficiency. Clinical endocrinology. 1999;51:517-24. PMID: 10583321
6. Hackney AC. Effects of endurance exercise on the reproductive system of men: the “exercise-hypogonadal male condition”. Journal of endocrinological investigation. 2008;31:932-8. PMID: 19092301
7. Basaria S. Male hypogonadism. Lancet (London, England). 2014;383:1250-63. PMID: 24119423