Veedma Health Blog

The relationship

Here is the simple setup. Men make testosterone which is the main male sex hormone that builds muscle, supports energy, and keeps erections firm. A part of that testosterone is turned into estradiol. Estradiol is a type of estrogen. It is a sex hormone that men also make in small but important amounts. Estradiol supports sex drive, mood balance, and bone strength in men. Some clinics treat estrogen like poison and try to drive it to zero. That idea can backfire.

Low T guys often chase testosterone replacement to fix low testosterone symptoms like no sex drive, weak morning erections, low energy, high belly fat, low focus, or feeling flat with no push. These are classic low testosterone symptoms. Many men are then given an aromatase blocker right away to “keep estrogen down.” That drug is often anastrozole. A aromatase inhibitor is a drug that blocks aromatase, which is the enzyme that turns testosterone into estradiol. A common sales pitch is that estrogen in men causes bloat, breast tissue, and mood swings. But research in men shows that estradiol is not just bloat. It is a driver of sexual desire, body composition, and physical function. In a National Institutes of Health funded trial that shut down the body’s own hormones and then added back controlled doses, both testosterone and estradiol were needed to keep sexual function normal in men. When estradiol was too low, desire dropped and body fat rose. [1]

Bones also need estradiol. Bone is alive. Old bone gets broken down and rebuilt every day. Bone mineral density means how solid and mineral rich the bone is. If bone mineral density drops, bones crack with smaller hits. Trials in older men with low testosterone found that blocking estradiol with daily anastrozole for months led to a drop in spine bone mineral density compared with placebo. [2] A later study in men age 65 to 82 with low testosterone showed that keeping estradiol from dropping was required to hold bone strength and normal gait speed. [3]

How it works

The body keeps balanced hormones in men with a loop of signals between brain, testicles, fat tissue, muscle, and bone. Your brain tells your testicles how much testosterone to make. Some of that testosterone turns into estradiol in fat tissue, muscle, and even in bone. That estradiol then talks back to the brain and the rest of the body. This is why men need estradiol, and why men need estrogen at healthy levels, not zero.

Here is what is going on under the hood.

Testosterone turns into estradiol

Aromatase is an enzyme. An enzyme is a protein that speeds up a chemical step. Aromatase turns testosterone into estradiol inside male tissue like fat, bone, and the brain. In real men, not mice, shutting down aromatase with drugs like anastrozole drops estradiol and changes body fat, bone, and sexual function. [1,2]

Estradiol feeds desire and erection quality

Libido means sexual desire or drive to seek sexual contact. In a controlled trial, men who lost estradiol saw a clear drop in sexual desire and overall sexual function. The study found that both testosterone and estradiol work together on sex drive and erections. [1]

Estradiol protects bone strength

Blocking estradiol in older men with low testosterone with daily anastrozole for twelve months led to lower spine bone mineral density compared with placebo. [2] Another trial in men age 65 to 82 showed that testosterone gel helped spine bone mineral density, but aromatase blockade without estradiol support did not protect bone the same way, and gait speed also suffered when estradiol was suppressed. [3]

Too low vs too high: finding the middle

Most men feel best with estradiol in a middle range, often around 30 to 50 picograms per milliliter. That is not zero. This comes from clinic reports from men on testosterone replacement therapy. Clinical trials in men with low testosterone also show harm when estradiol is pushed too low, mainly in sex drive and bone. [1,2,3]

Here is the key lab line for context. Meta analyses and major society guidance say that men with symptoms such as low sex drive, erectile trouble, low morning energy, and other low testosterone symptoms gain the most from testosterone replacement therapy when total testosterone is below about 350 nanograms per deciliter (about 12 nanomoles per liter). If total testosterone is borderline, check free testosterone. Free testosterone is the small part of testosterone that is not bound to proteins and can get into cells. Free testosterone below about 100 picograms per milliliter (about 10 nanograms per deciliter) supports a diagnosis of hypogonadism, which means under active testicles and low androgen action. [4,5]

Conditions linked to it

Here are the main clinical problems tied to very low estradiol in men, and why men need estradiol for normal function.

Sexual dysfunction. When estradiol drops too far, desire, arousal, and performance can fall. Men in suppression studies where estradiol was blocked reported worse sexual desire and worse total sexual function. [1] In men with epilepsy and sexual dysfunction plus low testosterone, blocking aromatase changed estradiol levels and altered sexual scores, which shows estradiol is an active player in male sexual function, not a passive bystander. [6]

Bone loss and fracture risk over time. In older men with low testosterone, daily anastrozole for a year lowered estradiol and led to a drop in spine bone mineral density versus placebo. [2] Another randomized trial in men age 65 to 82 confirmed that estradiol made from testosterone is required to hold bone mineral density and physical function such as fast walking speed. [3] Low bone mineral density means weaker bone structure and higher break risk in real life falls, so bone health and estrogen is a real concern for aging men.

Body fat and muscle balance. Men in a tightly controlled trial showed that estrogen deficiency drove up body fat. [1] Testosterone mainly protected lean mass and strength. Estradiol mainly kept fat gain in check. [1] This matters for metabolic health, because belly fat links to higher blood sugar and worse heart risk in midlife men.

Limitations: Most of these data come from older men, and from short controlled studies where hormones were pushed very high or very low on purpose. [1,2,3] We still need longer data in younger men on modern testosterone replacement therapy who may be taking weekly shots or daily cream plus anastrozole from a clinic. That means we should be honest about what we know and what we do not know yet.

Symptoms and signals

These are common red flags in men on testosterone replacement therapy, or men with very aggressive estrogen blocking, who may have pushed estradiol too low. Some also show up in men with untreated low testosterone and low free testosterone.

• Sex drive drops hard. You feel no pull to start sex or even think about it. This links to estradiol and libido. [1]
• Morning erections fade or feel weak. [1]
• You feel dry in the joints. Knees, hips, or shoulders may feel tight or clicky during warm up. Loss of estradiol can stress connective tissue in some men. [2,3]
• You gain belly fat fast even while on testosterone. [1]
• You feel flat, tense, or less motivated. Many men use words like numb, dull, or not themselves. This is widely reported in clinics, but long term mood data in younger men is still limited.
• Your lower back or ribs feel sore after light effort. Low bone mineral density raises concern for stress cracks over time. [2,3]
• You feel more tired during walking or stairs. Gait speed slowed when estradiol was blocked in older men. [3]
• Your labs show estradiol in the single digits while you are still on testosterone. That is a sign your aromatase inhibitor dose may be too strong.
• You are told you “need” anastrozole on day one of therapy, even when you have zero breast tissue changes, zero water retention, and zero high estradiol symptoms. That is a red flag and an aromatase inhibitors caution.

What to do about it

The goal is balanced hormones in men, not max testosterone and zero estradiol. Here is a simple three step plan that lines up with what current evidence and expert groups say.

1. Step 1. Test right. Get morning total testosterone and free testosterone measured twice with a high quality lab. Total testosterone below 350 nanograms per deciliter and free testosterone below about 100 picograms per milliliter, plus symptoms, supports clinical hypogonadism and the need to talk about testosterone replacement therapy. [4,5] Also ask for sensitive estradiol by LCMS, which is a lab method that can read low estradiol levels in men. The goal is not zero. It is control. You want to see if estradiol is in a workable range, often about 30 to 50 picograms per milliliter, according to many men on therapy who report good libido and joint comfort.
2. Step 2. Fix the cause, not just the number. Testosterone replacement therapy (often shortened to TRT) means giving medical testosterone to a man with proven low levels and symptoms to bring him back into a normal range, not to bodybuilder levels. TRT can raise sex drive, improve erection quality, improve lean mass, and improve overall sexual function in men with low testosterone at baseline. [1,4,5] If estradiol goes a little high and you get true symptoms like breast tissue swelling or ankle water that will not go away, then a low dose aromatase inhibitor may be reasonable for short control under a doctor. But blasting anastrozole by default in all men on TRT can push estradiol too low and harm bone mineral density and gait speed. [2,3] This is your aromatase inhibitors caution. Avoid any clinic that hands you anastrozole on day one even if you have no signs of high estrogen.
3. Step 3. Monitor and adjust, do not chase “perfect labs.” Recheck testosterone, free testosterone, estradiol, and basic safety labs on a schedule set by your licensed doctor. You want enough testosterone and enough estradiol to support sex, muscle, bone health and estrogen safety, mood, and day to day function. You also want to protect long term bone strength. [1,2,3] Make sure bone is on the radar. Ask about bone mineral density scans if you are older, if you have long term very low estradiol, or if you have ache or loss of height.

Myth vs Fact

• Myth: Estrogen is a female hormone. Men should crush it to zero because estrogen makes you soft.
  Fact: Men need estradiol for sex drive, erection quality, mood stability, and bone strength. [1,2,3]
• Myth: You always need an aromatase inhibitor with TRT to block estrogen.
  Fact: Routine anastrozole with no symptoms can drop estradiol too far, which can raise fat gain, reduce bone mineral density, and slow physical function. [1,2,3]
• Myth: If labs show “high estrogen,” that alone explains every bad feeling.
  Fact: Symptoms matter more than one lab. You judge the whole picture, including libido, erection quality, body fat, joint comfort, and bone health and estrogen status over time. [1,2,3]
• Myth: More testosterone always means better sex.
  Fact: Trials show that both testosterone and estradiol drive male sexual function. When estradiol is blocked, desire and total sexual function fall even if testosterone is high. [1]

Bottom line

Men need estradiol. Cutting estradiol too hard can ruin the very goals that drove you to TRT in the first place: sex drive, confidence in bed, steady mood, bone strength, and physical function. Strong data in men shows that both testosterone and estradiol work together on sexual function, body fat control, gait speed, and bone mineral density. [1,2,3] The smart play is not “zero estrogen.” The smart play is balanced hormones in men with steady testosterone, steady estradiol, symptom relief, and long term bone protection.

References

1. Finkelstein JS, Lee H, Burnett-Bowie SA, Pallais JC, Yu EW, Borges LF, Jones BF, Barry CV, Wulczyn KE, Thomas BJ, Leder BZ. Gonadal steroids and body composition, strength, and sexual function in men. N Engl J Med. 2013 Sep 12;369(11):1011-1022. doi:10.1056/NEJMoa1206168. PMID: 24024838.
2. Leder BZ, Rohrer JL, Rubin SD, Gallo J, Longcope C. Effects of aromatase inhibition on bone mineral density and bone turnover in older men with low testosterone levels. J Clin Endocrinol Metab. 2009 Apr;94(4):1379-1385. doi:10.1210/jc.2008-2153. PMID: 19820017.
3. Dias JP, Melvin D, Simonsick EM, Carlson O, Shardell MD, Ferrucci L, Chia CW, Basaria S, Egan JM. Effects of aromatase inhibition vs. testosterone in older men with low testosterone: randomized-controlled trial. Andrology. 2016 Jan;4(1):33-40. doi:10.1111/andr.12126. PMID: 26588809.
4. Park HJ, Park NC, Kim TN, Park K. Evolution of Guidelines for Testosterone Replacement Therapy. J Clin Med. 2019 Jan 10;8(1):35. doi:10.3390/jcm8010035. PMID: 30634448.
5. Davidiuk AJ, Broderick GA, McGreal TJ, Hackett G, Mulhall JP. Adult-onset hypogonadism: evaluation and role of testosterone replacement therapy. Transl Androl Urol. 2016 Dec;5(6):824-833. doi:10.21037/tau.2016.11.14. PMID: 28078213.
6. Herzog AG, Farina EL, Drislane FW, Schomer DL, Smithson SD, Fowler KM, Dworetzky BA, Bromfield EB. A comparison of anastrozole and testosterone versus placebo and testosterone for treatment of sexual dysfunction in men with epilepsy and hypogonadism. Epilepsy Behav. 2010 Feb;17(2):264-271. doi:10.1016/j.yebeh.2009.12.003. PMID: 20096638.
7. Corona G, Rastrelli G, Morgentaler A, Sforza A, Mannucci E, Maggi M. Meta analysis of results of testosterone therapy on sexual function based on International Index of Erectile Function scores. Eur Urol. 2017;72(6):1000-1011. doi:10.1016/j.eururo.2017.04.025. PMID: 28434676.