T Nation

Estradiol: Why You Should Care


Since this is a subject that comes up time and time again, I decided to start this thread so we can easily refer people to this information.

From the beginning...

Estradiol is an estrogen. It is known on blood tests as E2. Many people (even doctors) simply call it estrogen.

Why it Matters

There are basically two reasons we care about estradiol.

The first is that E2 is a powerful testosterone receptor antagonist. What this means is that estradiol binds to androgen receptors and renders them useless. When testosterone binds to an androgen receptor, it activates the receptor and you get the effect you're looking for. When estradiol binds to that receptor, it blocks testosterone from binding, yet it does not active the receptor, so nothing happens.

This means that if your estradiol is high, no matter how much testosterone you have, it isn't helping you as it should because too many of your androgen receptors are blocked by estradiol and your free testosterone has no where to go. Testosterone can't do you any good if it doesn't have receptors available to activate.

It can even get worse... because high levels of estradiol can cause the downregulation of androgen receptors. This means that your body may respond to higher levels of estradiol by creating fewer androgen receptors as cells are replaced in normal regeneration. In other words, not only does estradiol block the available androgen receptors, it causes your body to produce fewer of them in the future! This is one reason why raising testosterone levels may not have any immediate effect. It may be that your receptors have downregulated and so you'll need to lower estradiol and increase testosterone in order to get your body to upregulate again and this takes time.

The second reason we care about estradiol is that you also have estrogen receptors and estradiol binds to them and causes them to activate. This is fine if you want to grow man boobs, store fat on your belly, and have an enlarged prostate, but not so good if you want to look and feel like a man.

Where It Comes From

Brushing aside the highly controversial subject of environmental estrogens, the primary pathway for estradiol production is via the conversion of testosterone by aromatase. This means that the aromatase enzyme binds to testosterone and chemically converts it to estradiol. Think about that for a minute. Realize that this conversion is a double whammy. In one process you're losing T and gaining E. Obviously this is not good.

This is where aromatase inhibitors (AI) like anastrozole (brand name Arimidex - aka "adex" etc.) come into the picture. They bind to the aromatase enzyme and prevent it from converting your testosterone to estradiol. They do not work directly on estradiol nor on estrogen receptors. It is SERM's like Clomid and Nolvadex that bind to estrogen receptors. SERM's and AI's are different animals, so don't get them confused.

So an AI gives you the double whammy in reverse. It prevents the loss of testosterone to conversion and consequently lowers your estradiol which helps keep your androgen receptors available for testosterone.

E Follows T

Here's where doctors fuck up. They forget that E follows T. As your T levels go up, so will your E levels. If you're not doing something to control your E (like taking an AI) then you aren't really going to get anywhere with higher T levels because your higher E levels are just going to cancel out any beneficial effect from the T. Like I said, your T can't do you any good if all your androgen receptors are bound with estradiol.

For those of us with "age related" low T, this is a serious issue because our bodies are naturally trying to keep T low and E high by pumping out aromatase.

If you're younger and have low T for some other reason, aromatase may not be as much of an issue, but it still matters.


Fat produces estrogen and aromatase; even in men. If you're carrying extra fat, one of the best things you can do to help your hormone balance is to lose the fat.

In Range does not equal Normal

One of the problems you're likely to face is the problem of doctors believing that any blood test value that is "in range" is "normal" and therefor fine. I wish it was that simple.

Let's look at testosterone values. The range for Quest is 241-847 ng/dL. But those values are derived simply by looking at the values of everyone who has a blood test for testosterone. What's normal for a younger man is to be in the higher end of the range. What's normal for an older man is to be in the lower end of the range. Well low T might be "normal" but that doesn't mean it's good! I may be an older guy, but why should I be happy with low T simply because it's normal? ALL men of all ages should be in the higher end of the range if they want to feel good and perform athletically and sexually as men.

The same holds true for estradiol. The range is 13-54 pg/mL but "normal" young men are at the low end of the range and that's where you want to be as well.

Trust me, if your T is 250 and your E is 50, you may be "in range" for both values, but you aren't going to feel good or have anywhere near the athletic and sexual performance that would have if your T was 800 and your E was 15.

Natural Variation

All populations exhibit variation. The average height for men might be 5' 10" but we all know guys who are much taller and much shorter. This same variation applies to T levels, E levels, and reactions to various therapies. In other words, while the principals I've outlined hold true in general, how they specifically apply to you will vary. Be smart and deal with it.

Ok, that's enough from me for now. This is just a basic primer; there's a lot more to this subject so use this as a springboard to do more research on your own.

I'm sure others here will have significant things to say as well.

Good luck!

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Thank you for this post. I have a close friend that he and I have been discussing the T to E issue, and now he can read this printout for as complete understanding.

I know when my TT was 1500 and my E2 was 105, I felt anything but manly. Life sucked until I got my E2 back below 30.



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Very Helpful


This is an EXCELLENT narrative and very educational. If you could do one of these every few weeks I'd learn a lot...good job!


Well written, plain and understandable


This is really a great post. I'm very new to this and the post was almost like a T and E for Dummies lesson. Really appreciate the simple format and down to earth wording.


Thank you for this great explanation. I have been communicating with my doctor about why I want an estrogen level test and this will help explain why I want it.


Great post happydog. Much appreciated!


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Great article

My question is do younger males have natural aromatase inhibitors that allow for higher test levels but keep the estradiol in check?

It just seems that without an AI higher test levels = higher e levels and your screwed either way


great post.

Mods can we get this pinned?


I had the same question.

What causes T to aromatase more in some people than others?

Does adding T to your system do this?

How do some people have high T and normal E with out taking an AI? Do they lower concentrations of the enzyme responsible for aromatase?

Are there any medical studies or sources that explain this?

Tried to explain this to my Uro, but he shut me down with I have more T than you and it doesn't mean that my E is higher.


Aromatase, SHBG and E2 all tend to increase with age as TT drops and SHBG reduces the FT [%] fraction. Much of this has to do with gaining fat as result of the above changes, that leads to more of this decline. Even when weight does not change, muscle is lost and fat is gained. The BMI is not changing, but things are getting worse.

This type of response in a technical environment would be characterized as a system instability.

E is created by T-->E aromatization. The reaction rate is [somewhat?] bound by the availability of T. When you start TRT, E will go up, leading to more SHBG which reduces the FT levels from what they could be if E2 did not rise to elevated levels. Weekly injections or less frequent create T spikes that are followed by spikes in T-->E aromatization.

One's E response to T or increased T is very individualistic.

"""I have more T than you and it doesn't mean that my E is higher"""

Can just as easily be the opposite, which makes the statement's truth value meaningless.


Don't forget that your body is programmed to act in different ways at different ages. When you're a young adult, your body is programmed to keep T high and E low. The amount of aromatase you naturally produce is low. As you get older, you naturally produce more aromatase which starts to drive T down and E up.


Thanks Bushy, yeah it's all me. When I read research papers and studies at pubmed and such, I'm always translating the jargon into "plain English" in my own head. Most of this stuff is fairly easy to understand once you get past the jargon and especially if you have an educational background in biology, which I do.


Hey, "Amused K-9": I am definitely on the older side of the house. I've been using a mild AI this month and have been feeling more density in the muscles and having more productive workouts than in many months, so you are obviously on to something here!. Now this coming month (May) I'm going to run a "natural" protocol based on the recent "Question of Strength" article by Poliquin, specifically the section "No More Moobs". I'll be sytematically introducing what he suggests: ZMA, extra fiber, DIM, D-Glucarate & grape seed, as well as whats left of my REZ-V stash, on top of my usual supps. We'll see if this works, at least for me, and review/evaluate such at the end of the month...



Might have some relevant information...



You mentioned "This is one reason why raising testosterone levels may not have any immediate effect. It may be that your receptors have downregulated and so you'll need to lower estradiol and increase testosterone in order to get your body to upregulate again and this takes time."

How long can this process take. I've been taking Adex for 35 days to raise my testosterone. I've slowly noticed a difference. I just started testosterone injections today. I'll be doing those weekly.

I've had varicoceles / low testosterone for at least 6 years.


Unfortunately, it's impossible to say, but a time frame of "months" is reasonable to expect.

If I were you, I'd also be taking acetyl L-carnitine as there is good science coming in on its ability to help with androgen receptor upregulation. I buy it by the pound from Bulk Nutrition. Don't bother with capsules.

Don't get discouraged. Our bodies are incredibly complex and it takes time to get everything dialed in. You just have to be patient and keep at it.

Good luck!