Longitudinal analyses showing no influence of baseline hormone levels on change in anthropometric measures imply that body composition affects hormone levels and not the reverse.[10] The results of these cross-sectional analyses suggest that higher levels of E2 and the ratio of E2/T in men are associated with greater fat mass, whereas higher levels of T and to some extent SHBG are associated with lower fat mass.[10] However, other studies have reported no association between E2 levels and lean mass, muscle mass, or muscle strength in men.[10]

Most studies have shown inconsistent or no association of the estradiol level with muscle strength or physical performance in men.[1] In men, estradiol levels were not consistently related to muscle strength or physical performance, suggesting that circulating estrogen is not a primary determinant of muscle strength in community-dwelling men.[1] However, estradiol administration to ovariectomized rats decreases muscle mass and isometric contractile force, but this animal finding does not directly translate to men.[1]

By administering a variety of testosterone doses with and without concomitant aromatase inhibition, we found that changes in lean mass, thigh-muscle area, and leg-press strength were attributable to changes in testosterone levels, whereas changes in fat measures were primarily related to changes in estradiol levels.[11] By examining these relationships with and without suppression of estrogen synthesis, we found that lean mass, muscle size, and strength are regulated by androgens; fat accumulation is primarily a consequence of estrogen deficiency; and sexual function is regulated by both androgens and estrogens.[11] More than 80% of circulating estradiol in men is derived from the aromatization of testosterone. Thus, as serum testosterone levels decline, there is a concomitant decline in serum estradiol levels.[11]

Appendicular skeletal mass (ASM) was positively associated with total testosterone, free testosterone, and total estradiol, but not with free estradiol.[12] Testosterone level was related to both muscle mass, strength and physical performance. Total estradiol level, though related to muscle mass positively, affected muscle strength adversely in older men.[12] These data indicate that in older men, testosterone is the primary sex hormone related to muscle mass and function, while estradiol has a more complex and partly adverse relation to muscle strength.[12]

First, our results indicate that increases in serum levels of total testosterone and estradiol were associated with significant increases in abdominal muscle mass in men.[6] In fact, our data indicate that the associations were stronger for estradiol than total testosterone with abdominal muscle mass to include both stabilizing and locomotor muscles.[6] Our study found that higher levels of estradiol were significantly associated with higher levels of all abdominal muscle areas.[6]

These studies have shown that specific blockade of the aromatase enzyme for 10 weeks did not have catabolic effects on protein metabolism or intermediate metabolism of substrates, and it did not affect body composition, quantifiable measures of muscle strength, or bone calcium metabolism in healthy eugonadal young men.[4] In conclusion, these data suggest that in the male (1) estrogens do not contribute significantly to the changes in body composition and protein synthesis observed with changing androgen levels; (2) estrogen is a main regulator of the gonadal-pituitary feedback for the gonadotropin axis.[4] Thus, changes in estrogen alone, via aromatase inhibition, did not produce major changes in muscle mass or strength in these men.[4]

Randomized controlled trials have demonstrated a decreasing lean mass in healthy men due to both short- and long-term suppression of endogenous testosterone and 17β-estradiol production… Physiological levels of testosterone were associated positively with lean mass in younger and older men, and baseline serum testosterone and 17β-estradiol levels were associated positively with handgrip strength in older men… High serum 17β-estradiol, but not serum testosterone, was associated with higher lean mass in 3014 Swedish men aged 69 to 80 years.

Elderly men within the lowest quartile of free E2 had 0.5 kg less lean mass in the legs than subjects within the highest quartile, while the subjects in the different quartiles of free testosterone did not differ in lean mass… Serum E2, but not serum testosterone, is directly associated with lean mass in this large study of elderly Swedish men.

In women, estradiol and free testosterone levels are negatively associated with low muscle mass.[2] In men, elevated total testosterone was unexpectedly associated with an increased risk of low muscle mass (LMM).[2] Estradiol (E2) and total testosterone (TT) showed no significant association with low muscle mass in the continuous model, and this association was not observed in men.[2] Our study demonstrates that elevated SHBG levels associate with increased low muscle mass risk.[2]

Estradiol deficiency clearly predisposes males to increased adiposity and metabolic dysregulation.[1] These observations indicate that estradiol modulates body weight and adiposity in men. Notably, estrogens have important effects on glucose homeostasis, insulin sensitivity, and lipid metabolism in males.[1] In men, estrogen deficiency rather than excess appears to contribute to obesity and metabolic disease.[1]

Appendicular skeletal mass (ASM) was positively associated with total testosterone (TT; P<0.001), free testosterone (FT; P<0.001), and total estradiol (P<0.001) but not with free estradiol (P=0.102). Testosterone was related to both muscle quantity and quality. It was positively correlated with muscle mass and was associated with muscle strength and physical performance independent of muscle mass. Total estradiol level, though related to muscle mass positively, was associated with weaker muscle strength in older men.

In men, both total testosterone (TT) (Model 3: OR = 1.003, 95% CI: 1.002–1.004, p < 0.001) and free testosterone (Model 3: OR = 1.007, 95% CI: 1.001–1.013, p = 0.022) levels correlated positively with low muscle mass… Conclusions: In women, estradiol and free testosterone levels are negatively associated with low muscle mass. In men, elevated total testosterone was unexpectedly associated with an increased risk of low muscle mass (LMM). SHBG elevation is a consistent risk factor across sexes.

Testosterone increases muscle mass and reduces fat mass in vivo.[8] However, it is now clear that much of these effects are due to its conversion into estradiol.[8] Thus, estradiol contributes to some of the anabolic and body composition effects traditionally attributed to testosterone rather than causing muscle loss.[8]

Chronic exercise decreased androgens and estradiol in females but increased androgens in males… Intramuscular androgens were positively associated with muscle mass and strength in males… Associations between circulating physiological concentrations of testosterone and lean body mass have been found in males… High serum 17β-estradiol, but not serum testosterone, was associated with higher lean mass in 3014 Swedish men aged 69 to 80 years.

Estrogen deficiency results in loss of muscle mass through apoptotic mechanisms. Inconclusive evidence that loss of estrogen affects muscle protein turnover. Lack of estrogen impairs muscle regeneration ultimately impacting force generation. Although this review focuses on females, it summarizes evidence that loss of estrogen is associated with reduced muscle strength and mass, suggesting estrogen has a supportive role in muscle tissue.

All together, the existing data suggest that acute treatment with estrogen does not improve basal muscle protein synthesis; however, estrogen increases the anabolic response to exercise and this may result in the increase in muscle mass reported in long term studies. The review concludes that estrogen may have beneficial effects on muscle performance, but the evidence is mainly in women and animal models, and mechanisms include modulation of muscle repair and contractile function rather than simple changes in body composition.

Overall, they found that changes in lean mass, thigh muscle, and leg strength were attributable to changes in testosterone levels, while changes in fat measures were primarily related to changes in estrogen, they wrote. Decreases in lean body mass and muscle area and strength didn't develop until testosterone levels became quite low, at either 1.25 g or on placebo, they wrote. Finkelstein and colleagues concluded that the results imply testosterone levels regulate lean body mass, muscle size and strength, while estrogen levels regulate fat accumulation.

Our data suggest that total and free estradiol, % IBW, and fat-free mass are important positive determinants of BMD, while VO2 max is an important negative determinant of BMD at the spine in male collegiate athletes… Percent IBW and fat-free mass were also important predictors of BMD in the athletes studied, reflected in higher BMD at all sites in the wrestlers compared to the runners, and confirming the importance of weight and muscle mass as a determinant of BMD… We demonstrated lower total and free estradiol levels in male long-distance runners compared to wrestlers.

Low testosterone? Low estrogen too may cause problems for men. Reduced testosterone levels alone were enough to degrade a man’s lean body mass, the size of his thigh muscle or his leg strength. Those weren’t further degraded when a man’s ability to convert testosterone to estrogen was blocked, suggesting that these problems are largely caused by low testosterone alone. The accumulation of body fat was seen in most of the men whose testosterone was less than fully replaced, but such increases were particularly widespread in those whose estrogen levels were low.

Estrogen in men is important for modulating libido, erectile function, and spermatogenesis.[3] Having too much estrogen can cause problems such as infertility, gynecomastia, erectile dysfunction, and shrinking muscle mass.[3] Low estrogen in men can also cause issues, including increased body fat and decreased sexual desire.[3]

But, most experts agree that the normal male range for the main form of estrogen, called estradiol, is about 10 pg/mL to 50 pg/mL.[4] A few health conditions can cause high estrogen in men. These include diabetes, overactive thyroid (hyperthyroidism), and liver scarring (cirrhosis).[4] Tumors in the adrenal glands and tumors in the testes can also cause high estrogen. Obesity can raise estrogen levels, but some research suggests that it does not raise them above the normal range.[4]

It is reported that resistance exercise acutely augments the activity of the aromatase enzyme which results in an increase in the biosynthesis of estrogen from androgens.[7] This helps explain how a resistance exercise–induced testosterone increase can lead to an increase in estrogen levels, via increased aromatization.[7] The article describes acute hormone responses to resistance exercise but does not state that having chronically low muscle mass causes estrogen levels to become abnormally high in men.[7]

Both hormones contribute to the well being of skeletal muscle and bone in men and women, and there is evidence that the loss of sex hormones is associated with the age-related decline in bone and skeletal muscle mass… As would be expected, testosterone values are high in men and low in women, and estrogen values are high in women and low in men.

All these data suggest that serum E2 levels of 20 pg/mL or above are needed for optimal skeletal maturation and achievement of optimal peak bone mass… This threshold is very close to that required also for the epiphyseal closure… Recently Khosla et al. stated that a serum E2 level at least above 25 pg/mL is certainly protective for bone in men.

Men with low estrogen levels have higher levels of internal (visceral) abdominal fat, which is known to increase the risk of cardiovascular disease, diabetes, and metabolic syndrome. In addition, men with estrogen deficiency have reduced bone strength and an increased risk of bone fractures. This overview emphasizes that estrogen in men is important for fat distribution and bone health; it does not state that low muscle mass causes estrogen levels to become abnormally high.

Too much estrogen in men can cause infertility, erectile dysfunction and enlarged breasts. Too little estrogen can lead to a low sex drive. Obesity increases aromatase activity, which converts testosterone to estrogen, and can lead to higher estrogen levels in men; other causes of high estrogen include certain medications and tumors. The article does not link low muscle mass per se to abnormally high estrogen levels.

For this reason, having extra body fat is one reason some men may express higher-than-average estradiol levels.[12] Body composition – Most aromatase is made in body fat. Simply put, the more body fat you have, the more aromatase your body makes. This can lead to higher estrogen levels.[12] Low testosterone can actually cause the body to make more estrogen. Because testosterone and estrogen levels are closely interlinked, a sudden increase in testosterone from testosterone replacement therapy could result in a rise in aromatase and more estrogen.[12]

Increases in estrogen in males can also be an indicator of conditions such as diabetes, tumors of the adrenal glands or testicles, hyperthyroidism, or cirrhosis.[13] Aromatase excess syndrome and alcohol use disorder may be causes of increased estrogen in males.[13] Levels of estrogen that are too high or too low can cause problems in males. Low or high levels of estrogen can be indicators of underlying health problems.[13] The article lists numerous causes of high estrogen in men, but it does not mention low muscle mass as a causal factor.[13]

In this community-based sample, consisting of generally overweight but well-functioning men, greater estradiol levels were significantly associated with higher odds of reporting incident “fair” or “poor” self-rated health.[5] Higher estradiol levels were also associated with worse mobility outcomes in older men.[5] These findings suggest that higher circulating estrogen levels in men are linked to poorer self-reported health and mobility, but the direction of causality remains uncertain.[5]

The causes of high estrogen in men may be complex and related to a variety of conditions. For some, it is related to age, as estrogen levels rise naturally with time.[15] In others, obesity may play a role; since body fat contains aromatase, the additional fat leads to increased conversion of testosterone to estrogen.[15] High estrogen is also associated with fatigue and lack of energy, mood changes, increased body fat, loss of muscle mass, and enlarged prostate.[15]

According to the study summarized here, more than 80 percent of male estrogen is derived from the conversion of testosterone to estrogen.[3] As a result, the level of testosterone circulating in the bloodstream is hugely responsible for the amount of estrogen that will be found in the blood. Therefore, a decline in serum testosterone will also result in a deficiency of serum estrogen.[3] The study found that deficiency in testosterone levels in males results in decrease in muscle size, lean body mass, and strength, while deficiency of estrogen in males is primarily responsible for increase in body fat.[3]

The visible consequence of more estradiol on a man's body is the abnormal growth of breast tissue: gynecomastia. This abnormality occurs when the testosterone level decreases. Then the estrogen level increases to feminise the man. Reduce abdominal fat: Testosterone is converted directly to estrogen in abdominal fat by the action of the enzyme aromatase. It is not a coincidence that obese men have prominent breasts due to breast fat. Work out regularly: building muscle stimulates the production of testosterone and testosterone counteracts the effects of oestrogen. This is because testosterone and estrogen levels are interrelated (when one increases, the other decreases).

Higher body fat levels lead to increased estrogen synthesis, because adipose tissue contains the aromatase enzyme that converts testosterone into estradiol.[9] If you notice your muscle gains have stagnated, a low testosterone and higher than normal estrogen level may be the culprit.[9] Estrogen dominance in men is often a consequence of excessive body fat and aromatase activity rather than directly caused by low muscle mass.[9]

Some men experience increased abdominal fat, loss of muscle mass, or find it harder to build muscle even with exercise as potential signs of low estrogen.[14] This clinical practice site suggests that low estrogen in men may be associated with loss of muscle mass, not with high estrogen.[14] It does not describe low muscle mass as a cause of abnormally high estrogen levels in men.[14]

Increased aromatase activity in adipose tissue can raise circulating estradiol levels in men, and this is often observed in men with higher fat mass or obesity. Reduced muscle mass is frequently accompanied by increased fat mass with aging or physical inactivity, so changes in body composition can indirectly affect estradiol levels through aromatization rather than low muscle per se being a direct cause of abnormally high estrogen.

Estrogen is involved in maintaining muscle mass and strength in men. Low estrogen levels can lead to muscle loss and reduced physical performance. However, high estrogen in men is more commonly associated with obesity, metabolic syndrome, or exogenous estrogen exposure rather than with low muscle mass itself. This health-education article describes symptoms of low estrogen in men but does not claim that low muscle mass causes estrogen levels to become abnormally high.

Estrogen replacement improves myosin function and strength in muscle that is devoid of sex hormones, and the content of estrogen receptors in muscle also increases.[6] All together, the existing data suggest that acute treatment with estrogen does not improve basal muscle protein synthesis; however, estrogen increases the anabolic response to exercise and this may result in the increase in muscle mass reported in long term studies.[11] These mechanistic and performance-oriented reviews focus on estrogen’s effects on muscle, but they do not claim that low muscle mass in men causes estrogen levels to become abnormally high.[6][11]