Estrogen in Men: Why Lower Is Not Always Better During Testosterone Therapy

There is a familiar pattern in some corners of men’s hormone therapy. Testosterone is prescribed. hCG is added to preserve testicular function or size. An aromatase inhibitor is added to keep estrogen down. The drugs may be adjusted, but the underlying protocol remains largely the same from one man to the next.

The concern usually sounds reasonable enough. Testosterone can convert into estradiol. Estradiol is an estrogen. Too much estrogen can cause breast development. Therefore, keeping estradiol low should make testosterone therapy safer and more masculine.

The problem is that male physiology does not work that way.

Men are not designed to have zero estrogen, and estradiol is not an accidental contaminant of testosterone production. Aromatization is one of the normal ways the male body uses testosterone. Blocking that pathway can alter physiology in ways that additional testosterone does not necessarily correct.

Estrogen Is a Male Hormone Too

Adult men produce estradiol both directly and through peripheral conversion of testosterone and other androgens. Most circulating estradiol in men comes from aromatization outside the testes, including in adipose tissue, muscle, bone, and other tissues.

Aromatase is also present within tissues themselves, which means estradiol biology cannot always be understood from a serum number alone. Testosterone entering a tissue may be converted locally to estradiol and act there before a blood test ever tells us much about that local activity.

This is one reason testosterone and estradiol are better understood as related parts of male sex-steroid physiology rather than opposing hormones.

We already accept a similar idea when interpreting total testosterone, free testosterone, and SHBG. A single laboratory value rarely tells the entire story. Estradiol deserves the same level of clinical context.

The Experiment That Changed the Conversation

One of the most important studies in this field was published in The New England Journal of Medicine in 2013 by Joel Finkelstein and colleagues at Massachusetts General Hospital.

The investigators temporarily suppressed natural gonadal hormone production in more than 400 healthy men and replaced testosterone at different doses. In half of the men, they also gave anastrozole to prevent testosterone from being converted into estradiol.

For perhaps the first time in a large controlled human experiment, researchers could begin separating what testosterone itself was doing from what depended on the estradiol produced from testosterone.

The results did not fit neatly into the idea that testosterone is the useful male hormone and estrogen is something to control.

Loss of lean mass, muscle size, and strength was driven primarily by androgen deficiency. Increases in body fat were driven substantially by estrogen deficiency. Sexual function depended on both testosterone and estradiol.

Men who were prevented from aromatizing testosterone accumulated more body fat despite receiving testosterone. Sexual desire and erectile function also deteriorated as estradiol became very low. In that experimental model, the decline in sexual desire was considerably greater when estradiol fell below approximately 10 pg/mL.

That does not make 10 pg/mL a treatment target. It shows why deliberately pushing a man toward very low estradiol is not physiologically neutral.

The Male Skeleton Has Been Telling Us This for Years

Bone may provide the clearest evidence that men need estrogen.

Human experiments that separately manipulate testosterone and estradiol have repeatedly shown that estradiol plays a major role in suppressing bone resorption in men. Testosterone matters for the skeleton too, but increasing testosterone does not fully replace estrogen signaling when aromatization is blocked.

A one-year randomized trial illustrates the problem particularly well. Older men with low or low-normal testosterone received either anastrozole or placebo. Anastrozole did exactly what it was supposed to do: testosterone increased and estradiol decreased.

Mean testosterone rose from approximately 319 ng/dL at baseline to 474 ng/dL after one year. Estradiol fell from approximately 15 pg/mL to 12 pg/mL.

Despite the higher testosterone, spinal bone mineral density declined in the anastrozole group.

The estradiol change was not enormous, which is part of what makes the study interesting. The trial does not prove that every man taking a small dose of an aromatase inhibitor will lose bone. It does show that chronically interfering with aromatization can have skeletal consequences even while testosterone looks better on the laboratory report.

Population studies point in the same direction. In the MrOS Sweden cohort of more than 2,600 older men, lower estradiol was associated with greater fracture risk, with the relationship becoming particularly strong at total estradiol concentrations below approximately 16 pg/mL.

Again, 16 pg/mL should not become a universal treatment threshold. These studies tell us something more useful: very low estradiol is not desirable male physiology.

Bone health deserves particular attention in men receiving long-term hormone therapy. Hormones are one part of a much broader picture that includes resistance training, protein intake, vitamin D status, medications, age, genetics, and direct measurement when appropriate. We discuss that broader framework in Bone Density, Hormones, and Longevity.

Body Composition and Metabolism Are Part of the Story

Estradiol also appears to participate in the way men regulate body fat and glucose metabolism.

The Finkelstein experiment found that suppressing estrogen increased body fat even when testosterone was being replaced. The effect was not simply cosmetic. Adipose tissue, visceral fat, insulin sensitivity, and long-term cardiometabolic health are tightly connected.

A separate randomized crossover study took the question further. Seventeen healthy men received anastrozole and placebo for six weeks while researchers measured insulin sensitivity using a hyperinsulinemic-euglycemic clamp, one of the more rigorous methods available for studying glucose disposal.

Anastrozole lowered estradiol and modestly increased testosterone. Peripheral insulin sensitivity worsened.

It was a small mechanistic study, so it should not be turned into a claim that aromatase inhibitors cause diabetes. It does add to the evidence that estradiol has metabolic activity in men and that suppressing it cannot be assumed to improve health simply because testosterone rises.

That fits naturally with the way we think about body composition and insulin resistance and metabolic health. Testosterone therapy should not be judged by testosterone levels alone. Visceral fat, lean mass, glucose regulation, blood pressure, lipids, sleep, exercise, and cardiovascular risk remain part of the same patient.

More Testosterone Does Not Always Fix Low Estradiol

The sexual-function data may be the most counterintuitive for men who have been taught to fear estrogen.

Testosterone is unquestionably important for male libido and sexual physiology. The controlled human data also show that estradiol contributes independently to sexual desire and erectile function.

This becomes clinically relevant when a man on testosterone develops lower libido, poorer erections, joint discomfort, or simply feels worse after an aromatase inhibitor has been added. The reflex response is sometimes to increase testosterone further. If estradiol has been driven very low, more testosterone accompanied by continued aromatase blockade may not address the physiology that was disrupted.

The goal is not to diagnose every sexual symptom as an estrogen problem. Erectile function is vascular, neurologic, hormonal, metabolic, psychological, and medication-sensitive. Estradiol simply belongs in that conversation when it has been intentionally suppressed.

Does Higher Estradiol Feminize Men?

This is where much of the anxiety begins.

Estrogen can stimulate breast tissue, and significant estrogen excess can contribute to gynecomastia. Nobody needs to pretend otherwise. What gets lost is that gynecomastia is not determined by crossing one serum estradiol number.

Male breast tissue responds to the balance between estrogenic and androgenic signaling. Circulating estradiol, locally produced estradiol, testosterone, androgen-receptor activity, SHBG, adiposity, medications, liver function, thyroid disease, hCG production, and individual tissue sensitivity can all influence that balance.

A modest rise in estradiol as testosterone increases therefore does not mean a man is becoming feminized.

The American Urological Association specifically notes that estradiol commonly increases as testosterone increases during therapy and that symptomatic gynecomastia or other breast symptoms are uncommon. The guideline recommends estradiol testing particularly when men present with gynecomastia or breast symptoms rather than treating every increase in estradiol as an adverse event.

That is very different from prescribing an aromatase inhibitor in advance because estradiol might someday rise.

Aromatase Inhibitors Have a Role. Routine Suppression Is the Problem.

Anastrozole and other aromatase inhibitors are real medications with legitimate clinical uses. There are men for whom reducing excessive estrogen production is appropriate. They are also used selectively in reproductive endocrinology and male infertility because reducing aromatization can alter the hypothalamic-pituitary-gonadal axis and increase endogenous testosterone in certain circumstances.

That is not the same thing as making an aromatase inhibitor a standard companion to testosterone therapy.

One large sexual-medicine practice reviewed 1,708 men receiving testosterone therapy and found that only 44, about 2.6%, were treated with anastrozole for elevated estradiol. The authors also acknowledged something rarely mentioned in hormone marketing: the literature does not establish a clear estradiol cutoff at which men on testosterone should automatically receive estrogen-lowering treatment.

The absence of a universally validated cutoff should encourage clinical judgment, not more aggressive protocolization.

When estradiol appears excessive, it is also worth asking why. A testosterone dose producing supraphysiologic peaks may create more substrate for aromatization. Higher adiposity can increase aromatase activity. Alcohol, liver disease, thyroid disease, medications, and other endocrine conditions can change the androgen-estrogen environment.

Sometimes the better intervention is adjusting the testosterone dose or delivery schedule rather than adding another medication to counteract the first medication.

This is part of the broader principle we discuss in Medications, Hormones, and Longevity Medicine: treatment should solve a clinical problem, not simply create a larger protocol.

Where Does hCG Fit?

hCG is another medication that deserves to be separated from the automatic testosterone-hCG-aromatase inhibitor package.

hCG acts similarly to luteinizing hormone at the testes and can stimulate testicular testosterone production. It has important applications when fertility, spermatogenesis, or preservation of testicular function is a specific treatment objective.

Its use should be connected to that objective. The AUA/ASRM male infertility guideline discusses hCG, aromatase inhibitors, and selective estrogen receptor modulators as options for selected infertile men with low testosterone. It does not establish testosterone plus hCG plus an aromatase inhibitor as a universal men’s-health protocol.

Adding hCG may also increase the amount of testosterone available for conversion to estradiol. Automatically responding to that physiology with an aromatase inhibitor can turn hormone care into a sequence of medications being prescribed to manage the effects of other medications.

Estradiol Is Also Easy to Measure Badly

Male estradiol concentrations are relatively low compared with the concentrations commonly encountered in premenopausal women. That creates another problem: not every estradiol assay performs equally well at the low end of the range.

An Endocrine Society position statement on estradiol measurement has specifically highlighted the difficulty of accurately measuring the low concentrations found in men and in patients taking aromatase inhibitors. Direct immunoassays can lose accuracy and precision at these concentrations.

When a treatment decision depends on whether male estradiol is truly low, normal, or elevated, a sensitive method using liquid chromatography-tandem mass spectrometry, commonly abbreviated LC-MS/MS, can provide a more reliable measurement.

Timing matters too. A man using injectable testosterone may have very different testosterone and estradiol concentrations near the post-injection peak than he does before his next dose. Comparing laboratory results drawn at random points in the dosing interval can create apparent changes that have more to do with timing than physiology.

Good monitoring begins with knowing what was measured, how it was measured, and when it was measured.

There Is No Proven “Perfect” Estradiol Number for Every Man

Male hormone clinics sometimes promote narrow estradiol targets as though controlled trials have established an ideal number for every man on testosterone.

They have not.

Research gives us useful warning signals. Experimental studies suggest that very low estradiol can impair sexual function and accelerate adverse changes in bone. Prospective cohorts associate very low estradiol with fracture risk. None of those findings establishes a single universal estradiol target for every age, body composition, testosterone concentration, SHBG level, dosing schedule, or clinical circumstance.

The reference range should not be ignored, but neither should it become the patient.

A man with mildly increased estradiol, excellent clinical response, no breast symptoms, good sexual function, appropriate testosterone exposure, and stable metabolic and skeletal health is not the same patient as a man with rapidly rising estradiol, breast tenderness, gynecomastia, excessive testosterone exposure, or another endocrine abnormality.

Treating both men with the same aromatase inhibitor because their laboratory values crossed the same line is precisely the kind of protocol medicine that individualized hormone therapy is supposed to avoid.

How We Think About Estradiol at HormoneSynergy®

We occasionally see men who arrive at HormoneSynergy® already taking testosterone, hCG, and an aromatase inhibitor as part of a standardized male hormone protocol. Some have estradiol levels that have been pushed well below where we would normally expect them to be.

We rarely need routine aromatase inhibition in our own testosterone patients.

That does not mean we ignore estrogen. It means we do not assume aromatization is a problem before the patient gives us a reason to think it is.

We look at testosterone exposure, free testosterone and SHBG, symptoms, sexual function, breast symptoms, body composition, metabolic health, bone health, medications, fertility goals, and the way the hormone regimen is actually being administered. Estradiol is interpreted within that physiology rather than isolated from it.

If estradiol rises modestly as testosterone rises and the patient is doing well, that may simply represent normal aromatization. If estradiol is markedly abnormal, symptoms develop, or the pattern does not make physiologic sense, the answer is to investigate it rather than reflexively suppress it.

Sometimes an aromatase inhibitor is appropriate. Sometimes the testosterone dose needs to change. Sometimes injection frequency needs attention. Sometimes body composition, alcohol exposure, medication effects, thyroid function, liver health, or another endocrine issue is contributing.

The treatment follows the patient.

Estrogen Fear in Men Looks Familiar

Medicine spent years treating testosterone in women as though its presence were somehow masculine or abnormal. We now understand that women produce testosterone and require androgen signaling for normal physiology.

Men deserve the same nuance with estrogen.

Estradiol does not stop being biologically useful because the person producing it is male. Testosterone does not become dangerous to a woman simply because it is called an androgen. Sex hormones exist in both sexes, at very different concentrations and with different physiologic relationships.

There can be too much testosterone. There can be too little testosterone. There can be too much estrogen. There can be too little estrogen.

Good hormone medicine is not built around fearing either one.

The Bottom Line

Aromatization is not inherently a complication of testosterone therapy. It is normal male physiology.

The strongest human evidence shows that estradiol contributes substantially to male bone health, body-fat regulation, sexual function, and metabolic physiology. Deliberately reducing estradiol can therefore produce consequences that a higher testosterone level does not necessarily prevent.

There are legitimate reasons to use an aromatase inhibitor in selected men. There is far less evidence for giving one routinely to every man receiving testosterone in anticipation of a problem that may never occur.

The objective should not be the lowest possible estradiol number. It should be an appropriate hormonal environment for that particular man, measured carefully, interpreted in context, and changed only when there is a clinical reason to change it.

Frequently Asked Questions

Is estrogen important in men?

Yes. Estradiol participates in male bone metabolism, body-fat regulation, sexual function, and metabolic physiology. Much of a man's estradiol is produced through normal aromatization of testosterone.

Should estradiol automatically be lowered during testosterone therapy?

No. Estradiol often rises as testosterone rises, and a modest increase does not automatically require treatment. Aromatase inhibitors may be appropriate in selected situations, but routine preventive suppression is not established as standard testosterone therapy.

Does higher estradiol automatically cause gynecomastia?

No. Gynecomastia reflects the balance between estrogenic and androgenic activity in breast tissue and can be influenced by testosterone, estradiol, local aromatase activity, SHBG, medications, adiposity, liver and thyroid disease, and tissue sensitivity. Significant estrogen excess can contribute, but there is no single serum estradiol concentration that predicts breast development in every man.

Can estradiol become too low in men?

Yes. Human experimental data associate very low estradiol with increased body fat, poorer sexual function, increased bone resorption, and loss of bone mineral density. Aromatase inhibition has also reduced insulin sensitivity in a controlled human study.

What is the ideal estradiol level for a man on testosterone?

There is no universally validated optimal estradiol target for every man on testosterone therapy. Laboratory values should be interpreted alongside testosterone exposure, SHBG, symptoms, sexual function, breast symptoms, bone and metabolic health, treatment timing, and the clinical reason the test was ordered.

What type of estradiol test is best for men?

Because male estradiol concentrations are relatively low, sensitive testing is important when clinical decisions depend on the result. LC-MS/MS methods can provide better analytical performance at low concentrations than many routine direct immunoassays.

Selected References

Finkelstein JS, et al. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med. 2013;369(11):1011-1022. DOI: 10.1056/NEJMoa1206168.

Finkelstein JS, et al. Gonadal steroid-dependent effects on bone turnover and bone mineral density in men. J Clin Invest. 2016;126(3):1114-1125. DOI: 10.1172/JCI84137.

Burnett-Bowie SA, et al. Effects of aromatase inhibition on bone mineral density and bone turnover in older men with low testosterone levels. J Clin Endocrinol Metab. 2009;94(12):4785-4792. DOI: 10.1210/jc.2009-0739.

Gibb FW, et al. Aromatase inhibition reduces insulin sensitivity in healthy men. J Clin Endocrinol Metab. 2016;101(5):2040-2046. DOI: 10.1210/jc.2015-4146.

Mellström D, et al. Older men with low serum estradiol and high serum SHBG have an increased risk of fractures. J Bone Miner Res. 2008;23(10):1552-1560. DOI: 10.1359/jbmr.080518.

Rosner W, et al. Challenges to the measurement of estradiol: an Endocrine Society position statement. J Clin Endocrinol Metab. 2013;98(4):1376-1387. DOI: 10.1210/jc.2012-3780.

American Urological Association. Evaluation and Management of Testosterone Deficiency: AUA Guideline. Published 2018; validity confirmed 2024.

American Urological Association/American Society for Reproductive Medicine. Diagnosis and Treatment of Infertility in Men: AUA/ASRM Guideline. Published 2020; amended 2024.

Medical note: This article is educational and is not intended to replace individualized medical evaluation or treatment. Testosterone therapy, hCG, and aromatase inhibitors should be prescribed and monitored according to the patient's clinical circumstances, laboratory findings, treatment goals, and risk profile.