Estrogen plays a surprisingly central role in the male body, influencing everything from bone strength to sexual function to how fat is stored. Men produce estrogen naturally, with normal blood levels typically falling between 10 and 40 pg/mL. About 20% comes directly from the testes, while the rest is produced locally in fat tissue, brain, skin, and bone through an enzyme called aromatase that converts testosterone into estrogen.
How Men Produce Estrogen
The aromatase enzyme is the key player. Found in fat cells, bone, brain tissue, skin, and the testes themselves, aromatase takes circulating testosterone and chemically converts it into estradiol, the most active form of estrogen. Inside the testes specifically, aromatase is concentrated in the cells that produce testosterone (Leydig cells) and in developing sperm cells.
This means estrogen levels in men are partly tied to testosterone levels and partly to body composition. More fat tissue means more aromatase activity and higher estrogen production, which is one reason obesity shifts the hormonal balance in men.
Bone Strength Depends on It
Estrogen may actually matter more for male bone health than testosterone does. Studies show that the correlation between bone mineral density and estradiol levels in men is stronger than the correlation with testosterone. Men with low circulating estradiol face a higher risk of fractures, particularly at the hip. Active estrogen metabolites are significant independent predictors of bone density at the hip, femoral neck, and surrounding regions.
Without adequate estrogen, men lose bone mass over time, which can progress to osteoporosis. This is one reason older men, whose estrogen levels gradually decline, become increasingly vulnerable to fractures.
Sexual Function and Desire
Estrogen’s role in male sexual function is more nuanced than most people expect. At the right levels, estradiol is essential for healthy libido, erectile function, and sperm production. In men with low testosterone (below about 300 ng/dL), sexual drive is markedly higher when estradiol levels remain above a certain threshold. One striking case report documented a man who lacked both aromatase and adequate testosterone: neither estrogen nor testosterone alone could restore his sex drive, but the combination of both did.
When men with low testosterone were given an aromatase inhibitor that eliminated their estradiol, their libido dropped, reinforcing that complete removal of estrogen harms sexual desire. However, the relationship flips when estrogen climbs too high. Elevated estrogen in men can independently increase the risk of erectile dysfunction, and this effect adds to whatever problems low testosterone is already causing. When erectile dysfunction is driven by high estrogen, testosterone therapy alone often fails to fix it as long as estrogen stays elevated.
Sperm Production and Fertility
Estrogen’s primary job in the male reproductive tract is regulating fluid balance. In the ducts that carry sperm from the testes to the epididymis, estrogen receptors control the reabsorption of fluid, which concentrates sperm as they mature. Without functional estrogen signaling, those ducts lose the ability to absorb water properly. The result is diluted, poorly formed sperm and reduced fertility.
Estrogen also helps maintain the structural integrity of the cells lining these ducts. Interestingly, estrogen doesn’t appear to be essential for sperm production itself. When sperm cells from estrogen-receptor-deficient mice were transplanted into normal testes, they developed into fully functional sperm capable of fertilization. So estrogen’s contribution to fertility is less about making sperm and more about creating the right environment for sperm to mature and survive.
Fat Distribution and Metabolism
Men typically accumulate fat around the abdomen (the “apple shape”), and estrogen activity plays a direct role in moderating this pattern. Higher estrogen levels promote fat storage under the skin rather than around the organs, which is metabolically healthier. When estrogen signaling is lost in males, both human and animal studies show increased obesity and impaired glucose metabolism.
In male mice, estradiol treatment reduced inflammatory markers in fat tissue and improved insulin sensitivity. Trans women receiving estrogen therapy develop a more feminine fat distribution with a lower waist-to-hip ratio, providing a visible demonstration of estrogen’s effect on where fat accumulates. Male fat tissue also responds differently to excess calories: it tends to expand by enlarging existing fat cells rather than creating new ones, which causes more cell death and inflammation. Estrogen helps counteract this inflammatory response.
Heart and Blood Vessel Health
Blood vessel cells in men carry estrogen receptors at densities comparable to women’s. A young man born without functional estrogen receptors developed both blood vessel dysfunction and coronary artery disease, providing early evidence that estrogen contributes to cardiovascular health in males.
In a study of older men who had very low hormone levels due to prostate cancer treatment, eight weeks of low-dose estradiol supplementation lowered both systolic and diastolic blood pressure, raised HDL (“good”) cholesterol, and enhanced the release of nitric oxide, a molecule that keeps blood vessels relaxed. The treatment also blunted the blood-vessel-constricting effects of angiotensin II and norepinephrine, two chemicals that raise blood pressure. These changes suggest estrogen helps protect male blood vessels through multiple pathways simultaneously.
Mood and Brain Function
Estrogen receptors are found throughout the male brain, and low estrogen in men has been linked to moodiness, irritability, trouble concentrating, and difficulty sleeping. However, the cognitive effects of estrogen in men are less dramatic than once hoped. A study examining estrogen treatment in male-to-female transsexuals found little measurable influence on memory, verbal ability, or spatial reasoning, despite initial expectations. The mood-related effects of estrogen appear to be more consistent than the cognitive ones: men with low estrogen commonly report fatigue, irritability, and poor sleep quality.
What Happens When Levels Are Too Low
Men with estrogen deficiency tend to experience a recognizable cluster of symptoms: increased belly fat, reduced sex drive, bone loss, dry skin, hot flashes, night sweats, trouble concentrating, moodiness, fatigue, and insomnia. These symptoms overlap significantly with what’s commonly attributed to low testosterone, which makes sense given that estrogen is produced from testosterone. Many men experiencing “low T” symptoms may actually be dealing with low estrogen as well.
What Happens When Levels Are Too High
Excess estrogen relative to testosterone causes its own set of problems. The most visible is gynecomastia, the enlargement of breast gland tissue. This occurs when the estrogen-to-testosterone ratio shifts in estrogen’s favor, whether from increased estrogen production, decreased testosterone, or both. Symptoms include swollen or tender breast tissue, sensitive nipples, and sometimes pain. Gynecomastia can affect one or both sides and doesn’t always develop symmetrically.
Beyond breast tissue changes, elevated estrogen independently increases the risk of erectile dysfunction, promotes fat gain, and can suppress the body’s own testosterone production through hormonal feedback loops. This is why aromatase inhibitors are sometimes used in men with documented estrogen excess, though driving estrogen too low with these medications creates its own problems, as the libido and bone health research makes clear. The goal is balance, not elimination.