The Best Estrogen Blockers for Men: How Aromatase Inhibitors Work

Natural Estrogen Blockers for Men: Which Aromatase Inhibitors Are Best?

We’ve talked a lot about testosterone and how it's the veritable “life force” for men. (Check out our Guide to Testosterone Replacement Therapy if you haven't already). In this article, we will switch gears and focus on testosterone's feminine counterpart, estrogen.

Elevated estrogen levels are common in men that take testosterone and those who are overweight. Consequently, men with high estrogen may experience numerous symptoms, one of which is gynecomastia, aka "man boobs."

So, what can you do to reduce estrogen levels if you're a man? Read on to learn about estrogen blockers for men and how aromatase inhibitors work.

Low Testosterone and High Estrogen in Men: Different Conditions with Similar Symptoms

Testosterone replacement therapy (TRT) is growing in popularity for treating low testosterone levels. The conundrum some men face is that estrogen levels tend to increase as testosterone levels do. As part of the steroidogenesis pathway, testosterone is metabolized into either dihydrotestosterone (DHT) by the 5-alpha reductase enzyme or estradiol by the aromatase enzyme.

Estradiol is the principal estrogenic hormone in men and women. Technically, the term "estrogen" broadly refers to three steroid hormones: estradiol, estrone, and estriol. These hormones all have feminizing (estrogenic) actions in the body, such as stimulating breast tissue growth.

An important biomarker for men's health is the ratio of testosterone to estrogen (estradiol). When the levels of estrogen are disproportionately high relative to testosterone, a range of symptoms may occur, including:

  • Unexpected weight gain and increase in body fat
  • Gynecomastia ("man boobs")
  • Loss of muscle mass
  • Erectile dysfunction
  • Low sex drive
  • Reduced sperm production

When a man has high testosterone levels, he won’t feel very "alpha" if estrogen levels are also sharply elevated. Estradiol and other estrogenic hormones compete for the same androgen receptors as androgens, and each androgen receptor only has so many binding sites available for these hormones to occupy.

As an analogy, think of the androgen receptor like a parking lot with a limited amount of open spaces for estrogenic and androgenic vehicles. Normally, only a handful of these spots are "reserved" for estrogen; the rest are for androgens like testosterone and DHT. But when a sudden influx of estrogen cars swarm the parking lot, they "steal" those androgen vehicles' parking spots.

Essentially, high estrogen levels prevent testosterone and other androgens from working their anabolic magic by occupying those precious parking spots (read: receptor binding sites). However, most men incorrectly assume that estrogen is inherently a "bad hormone" when it's actually quite the opposite. Men need small amounts of estrogen for proper health and longevity. In fact, men with low estrogen often experience symptoms comparable to having too much estrogen, notably decreased sex drive.

How Do Estrogen Blockers Work?

Estrogen blockers typically act as aromatase inhibitors (AIs), meaning they bind to the aromatase enzyme and deactivate it. Aromatase inhibitors reduce the conversion of testosterone into estrogen (estradiol) and androstenedione into estrone, the latter being a minor estrogenic hormone in men.

In clinical settings, aromatase inhibitors are often used for treating the early stages of breast cancer in women and gynecomastia in men. There are quite a few pharmaceutical aromatase inhibitors on the market, namely Arimidex (anastrozole), Aromasin (exemestane), Nolvadex (tamoxifen), and Femara (letrozole). These drugs are non-steroidal compounds that strongly blunt the aromatization of androgens. They can drastically reduce estrogen levels in a short amount of time, so you should only use them under medical supervision.

estrogen blocker for men

For most men, prescription estrogen blocker treatment is not necessary. Similar to natural testosterone boosters, like Transparent Labs Vitality, several natural estrogen blockers can help balance the ratio of androgenic to estrogenic hormone levels in the body without totally shutting down the endocrine system. The following section will break down the research highlighting naturally occurring compounds that act as estrogen blockers.

Natural Estrogen Blockers for Men

Vitamin D and Zinc

Multiple clinical studies have shown that vitamin D3 (cholecalciferol) is an important regulator of sex hormone production:

  • The active form of vitamin D, calcitriol, inhibits the growth of malignant breast cancer cells by down-regulating the expression of estrogen receptors [1].
  • One year of daily vitamin D3 supplementation at a dose of 3,332 IU increased total testosterone by an average of 33% and free testosterone by an average of 21% in 54 healthy adult men [2].
  • A cross-sectional study of over 2,200 men found that those with sufficient vitamin D levels had significantly greater total testosterone and lower sex-hormone-binding globulin (SHBG) than those deficient in vitamin D [3].

Zinc is an essential trace mineral found at the center of zinc finger proteins that make up all the nuclear steroid receptors in the body. A recent study found that one of these proteins, ZNF131, is a negative regulator of estrogen receptor signaling [4]. In other words, it suppresses estrogenic activity.

Likewise, men with low zinc levels consistently display lower androgen level readings, illustrating a definitive association between these two micronutrients and sex hormone levels. Healthy young men who followed a zinc-restricted diet for 20 weeks experienced a drastic decrease in total testosterone levels, falling to a mere 25% of baseline values [5].

Zinc deficiency is also well-known to adversely affect male fertility, likely by altering the ratio of testosterone to estrogen. Middle-aged sterile men that supplemented with 220 mg zinc (sulfate) daily for two had an average 250% increase in sperm count and 54% increase in total testosterone levels(the zinc supplement effectively restored fertility) [6]. However, more clinical data is needed to confirm the impact of zinc supplements on estrogen levels in men.

Grape Seed Extract (Proanthocyanidins)

The seeds of grapes (Vitis vinifera) are a rich source of proanthocyanidins and anthocyanidins, among a myriad of other phenolic compounds. The phytochemicals in grape seed extracts are revered for their antioxidant, antihypertensive, anti-diabetic, and anti-hyperlipidemic effects, in addition to being well-tolerated. According to several in vitro studies in human breast cancer cell lines, grape seed proanthocyanidins modulate estrogen levels by selectively inhibiting aromatase [7, 8].

Note that breast cancer cell lines are a gold standard for studying estrogen blockers since these cells express high amounts of the estrogen receptor. Thus, in vitro research using cancer cells from breast tissue is a primordial stage in discovering natural aromatase inhibitors like grape seed extract.

And the benefits of grape seed extract don't stop at controlling estrogen production. Several human studies suggest that grape seed extract can improve blood pressure and blood lipid profiles:

  • A 4-week, double-blind clinical trial of 27 adults with metabolic syndrome found that subjects who were given 150 mg grape seed extract per day had an average reduction of 9 points in systolic blood pressure and 3 points in diastolic blood pressure compared to baseline values [9]. Several of the subjects had greater than 15 point reductions in systolic blood pressure. Subjects were instructed to maintain the same diet and lifestyle during the trial as they did before the study. 
  • Another study of 61 healthy middle-aged adults found that oxidized LDL cholesterol dropped significantly by the end of the 12-week trial period in both grape seed extract treatment groups [10]. Those taking a placebo had relatively unchanged oxidized LDL cholesterol levels. These findings demonstrate the cardioprotective effects of grape seed extract, which may be useful in preventing heart conditions such as atherosclerosis. 

Rhodiola Rosea Extract

Rhodiola (Rhodiola rosea) is considered one of the most robust adaptogenic herbs, right alongside ashwagandha (Withania somnifera). Adaptogens are so named due to their versatile actions in the body, helping restore homeostasis by modulating the hypothalamic-pituitary-adrenal (HPA) axis after facing adverse stressors. Thus, rhodiola and ashwagandha are commonly used for controlling cortisol production, which directly supports a healthy testosterone-to-cortisol ratio.

However, a distinct characteristic of rhodiola root extract compared to other adaptogenic herbal extracts is that it contains salidroside and rosavin, two phytochemicals that have been shown to inhibit the aromatase enzyme [11]. Hence, rhodiola is a promising natural estrogen blocker for men/aromatase inhibitor. Supplementing with rhodiola extract can also encourage a proper balance of testosterone and estrogen in men by limiting the aromatization of the former.

As an added benefit, rhodiola has potent nootropic effects that make it an exceptional cognitive aid during the day.

DIM (Diindolylmethane)

3,3′-diindolylmethane (DIM) is a bioactive metabolite of indole-3-carbinol (I3C), a phytochemical found in cruciferous vegetables (e.g. broccoli and cauliflower). DIM appears to modulate estrogen metabolism by acting on the aryl-hydrocarbon receptor that regulates gene expression in men and women [12].

In vivo and in vitro data suggest that DIM also has favorable effects on muscle growth, recovery, libido, mood, and overall well-being by balancing estradiol levels[13, 14].

Calcium D-Glucarate

Animal studies have demonstrated that supplemental calcium-d-glucarate reduces estradiol levels by as much as 25% [15]. In the body, calcium D-glucarate serves as a slow-releasing reservoir of glucuronolactone, the latter of which appears to inhibit the actions of an enzyme called beta-glucuronidase.

Beta-glucuronidase is produced by bacteria in the colon and is responsible for breaking down certain carbohydrates. Excessive activity of this enzyme has been shown to decrease the rate at which estrogen metabolites are removed from the body [16]. 

Therefore, inhibiting beta-glucuronidase (via calcium D-glucarate) may help lower levels of estradiol and estrogen metabolites by increasing their rate of elimination [17].

Using an Estrogen Blocker

Hormone balance is essential to health and performance. If you decide to take an estrogen blocker supplement, remember to be consistent and regularly monitor your testosterone and estradiol blood levels. Having objective measurements will reassure you that the estrogen blocker is working as expected (or not).

Transparent Labs Vitality is a 3-in-1 hormone optimizing supplement that features clinical doses of natural ingredients discussed throughout this article, such as DIM, zinc, and organic ashwagandha root extract. It not only helps increase testosterone production but also controls the amount that is converted to estrogen. No need for a separate estrogen blocker. 

And lastly, always consult with a licensed physician, preferably one specializing in hormone replacement therapy, before taking a prescription estrogen blocker. The potential side effects of natural estrogen blockers are comparatively mild to those of pharmaceutical aromatase inhibitors.


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