STEP 5: Decide on a target estradiol level with your physician. Going too low will likely lead to osteoporosis and going too high may increase risk of arterial plaque, cancer, enlarged prostate and possibly prostatitis. I have a lot of pages on these subjects and I cover them here: Summary Page on Estradiol and Estrogen, so you can read more in depth there.
There is no magic "normal level" for any hormone from what I have seen that will work for every guy in every situation. That said, you don't want to go to the opposite extreme and decide that there is no such thing as high or low estradiol. The savvy physicians from what I have seen use a combination of symptoms and comparing your blood draw to a "normal," youthful level, which is what I am to discuss below.
Actually, I should also mention that the solid majority of physicians currently do not even pull estradiol in men. In general, this is due to ignorance. Unfortunately, doctors incorrectly think that estradiol is a "woman's hormone" and has little impact on us guys. This could not be more wrong and estradiol is every bit as powerful as testosterone. Sure, estradiol in us guys comes from testosterone, but that does not mean it is not important, and, fortunately, a couple of recent studies have highlighted this fact and brought it to the forefront of the medical community.
Most men, though, instinctively know that estradiol does actually matter, which is why the two most common questions that I get asked on the Peak Testosterone Forum are probably:
There is a lot of good data on #1, but very little on #2. As I have often discussed with other guys, men's issues seem to take a back seat in the research quite often!
However, the great majority of physicians have absolutely no idea that estradiol has such a powerful effect on men. For example, look at the story of this man, whose estradiol was actually above the lab range and yet his doctor would do nothing about it:
"This summer a test showed I had slightly elevated E2 (estradiol), my result was 181 pmol/l [49.3 pg/ml] and range 50-162 and nothing happened, no doctor seems to think this is an issue and so far refuse to even consider my problems to have anything with E2 to do...This autumn I meet a new doctor and he quickly changed from 12 week to 8 week injections and, well im not going to describe how it made me fell since i would need to curse in roughly 32 different languages to even get close. No erections at all not even soft, achieving orgasm was borderline impossible and orgasm didn't feel good at all, increased pain from toes to head, sleeping less good and some other problems. " 
And, while I am not a big fan of Arimidex (which lowers estradiol (E2), look at what happened to him when he started taking it:
"Then I made a request for Arimidex and thankfully my request was handled by a doctor either knowing what she did or more likely, didn't know what she did, either way I got a recipe for ~400 pills and supposed to take one a day. I noticed a change the first day but the second day, WOW my little weiner was alive again and the feeling was amazing, it was so hard it was almost painfull, i can honestly say it felt like I had forgotten how good it feels."
In any event, let's start with the assertion of my old HRT clinic. They claimed that generally men feel better when their estradiol levels fall between 20 to 30 pg/ml. The implication, of course, was that this range was the normal, healthy, youthful ranges for estradiol in men. I tend to believe them, because I have so often seen men on HRT end up higher than 30, then take Arimidex to get their level between 20 and 30 only to feel dramatically better. Of course, I disagree with this policy of my old clinic, because I do not think the vast majority of men should take Arimidex. I believe is risky for two reasons: a) it is easy to knock your estradiol down so low that you could end up with bone loss and b) it is a pharmaceutical that some experts believe, even in low doses, could increase the risk of clotting.
CAUTION: 20-30 pg/ml comes from the old way of measuring estradiol in men, which the labs are no longer using. More research needs to be done to correlate the old versus the new tests.
Nevertheless, I think the philosophy of not going too high or too low with estradiol is good. And I think this is shown in studies of estradiol in men by age. Just what are normal, youthful and healthy levels of estradiol in a male? Check out this data:
To answer these questions, we can go back to a 2000 Clinical Endocrinology study where they summarized a variety of hormone levels by age, including estradiol:
The above are in international units and not the standard pg/ml, so let me do that conversion for everyone reading this in the U.S. (The appropriate conversion factor is 3.671.)
Many of us would guess that estradiol levels would rise as we put on weight with aging, right? However, the data above shows that that is decidedly not the case and estradiol levels to tend to fall as the decades roll by. This is part of the reason that so many men end up with osteoporosis. And making the matter worse is that our SHBG levels climb, leaving us with less free estradiol as we age as well. (SHBG binds to estradiol as well as testosterone.)
Most importantly, notice that youthful estradiol levels are 28 pg/ml for men in the 20's and about 26 pg/ml for men in their 30's according to this study. This is a powerful argument that youthful estradiol levels fall right in the 20-30 range recommended by my old clinic.
Now someone might object and say, "But these included overweight and sick individual which would skew the results." Sorry, but the researchers were one step ahead of you and only "healthy, non-obese subjects" where allowed in the study. Average BMI was actually 24.6+/-2.5 kg/m^2. This means that the highest BMI man in the study was 27.1. So the argument seems weak that normal weight men tend to be high in estradiol. In fact, notice that at no age were natural average estradiol levels above 30 pg/ml.
It should be noted, though, that, just as testosterone symptoms can be variable from individual to individual, there is no doubt that estradiol symptoms and levels can fall in the same category. For example, the standard deviation in estradiol values for the 20-29 year olds was 23.43 pmol/. This means that the top threshold for "normal" estradiol, if we look at one standard deviation up from the mean, is 34.4 pg/ml. Thus, one could argue that youthful testosterone could be up to the mid 30's for a significant block of men. The point is not to come up with hard and fast rules but rather to point out that youthful estradiol levels are generally not overly high.
HUGE ISSUE: So then we can just target 20 to 30 or maybe 35 pg/ml, right? Unfortunately, the answer is probably no, and the reason is that the state of estradiol testing for men is in disarray. The labs are now pushing the LC-MS/MS test, which is righteous and good, but this technology generally reads significantly lower than the old immunoassays from what I have seen. This was shown in a study that compared the LC-MS/MS against 4 other immunoassays and the average results varied by up to 53%!  A number of the men have seen this on The Peak Testosterone Forum, i.e. a much lower estradiol score from the LC-MS/MS tests. Basically, the only worthwhile test is probably the LC-MS/MS, but we have no good research data showing what is high and low based on this test!
So we know we don't want to go too low with estradiol or we could end up with brittle bones and hip fractures like a lot of 75 year old women struggle with. Furthermore, common sense dictates that more is not better when it comes to estradiol. Many men who go on HRT and end up with estradiol in the 40's and 50's very commonly have a certain suite of side effects: gyno, water retention, lowered libido, loss of erectile strength, moodiness, poor sleep etc. If you've been around Peak Testosterone Forum at all, you know this is actually quite common. And many experts have concern about long term effects as well, because high estradiol may increase clotting risk, arterial plaque and prostate issues as I mentioned.
So what's a fella to do? Well, let me share my own story here. I am testosterone cypionate and my last testosterone read was 700 ng/dl at one lab and 800 ng/dl at another. So I'm somewhere around 750 ng/dl on a daily basis I inject my cypionate subQ every other day, so my levels should be quite constant and consistent. Yet my last estradiol read was 27 pg/ml without any Arimidex.
I think most men would be happy with that read via only natural means. So how did I do it? I simply did the following 3 natural methods:
Now the point of that story is that one I got my testosterone levels to a more reasonable level and dropped my body fat down to what it was in college, - low and behold! - my estradiol levels dropped into the range that they should be. I am 54 and so don't buy into the theory that, because you are a little older that you cannot control estradiol and, therefore, must to be on a pharmaceutical to control it.
So in my opinion the solid majority of guys on TRT can get their estradiol in line if they follow the above principals, and this is a far safer approach that just throwing Arimidex at the problem.
CAUTION: As I mentioned, there has been considerable debate about the best way to measure estradiol in men. Of course, our estradiol levels are very low and so you cannot just use the standard test, which is designed for premenopausal women with abundant estradiol. See my page on Which Estradiol Test is the Best? for more information. In addition, there is a recent study that shows HIV+ men may need higher levels of estradiol to maintain bone mass. 
1) Clin Endocrinol (Oxf), 2000 Dec, 53(6):689-95, "Age-related changes of serum sex hormones, insulin-like growth factor-1 and sex-hormone binding globulin levels in men: cross-sectional data from a healthy male cohort"
3) Clinical Chemistry, 2014, 60:3, "Performance of Direct Estradiol Immunoassays with Human Male Serum Samples"
4) Osteoporos Int, 2015 Oct 28, "Serum total estradiol, but not testosterone is associated with reduced bone mineral density (BMD) in HIV-infected men: a cross-sectional, observational study"