Does lower available testosterone lead to lower estradiol in men?

In men, the physiological relationship between testosterone and estradiol is governed by the conversion of androgens into estrogens, making the availability of testosterone a primary determinant of systemic estradiol levels.

Clinical and effectiveness evidence

For the majority of adult men, the circulating pool of estradiol is not a direct product of testicular secretion. Instead, quantitative physiological data shows that approximately 80% to 85% of circulating estradiol originates from the aromatization of testosterone and androstenedione in peripheral (extraglandular) tissues. The testes contribute only the remaining 15% to 20% of the total plasma pool. Consequently, there is a strong correlation between these two hormones; clinical research indicates that men with subnormal free testosterone concentrations typically exhibit significantly lower free estradiol levels (median 0.047 ng/dL) compared to those with normal testosterone levels (median 0.063 ng/dL).

Mechanistic explanations

This relationship is mediated by the enzyme aromatase, encoded by the CYP19A1 gene. Aromatase is expressed in various peripheral sites, including adipose tissue (fat), skin, bone, and vascular endothelium.

• Substrate Availability: Testosterone serves as the obligatory precursor for estradiol. As the primary substrate for the aromatase enzyme, any reduction in available testosterone—whether through age-related decline or hypogonadism—directly limits the raw material available for conversion.
• Enzymatic Conversion: While aromatase is present in the testes (specifically in Leydig and Sertoli cells) to support local spermatogenesis, the total volume of peripheral tissue, particularly adipose tissue, dominates the systemic conversion process.
• Response to Modulation: The dependency of estradiol on testosterone levels is further confirmed by clinical interventions. When testosterone levels are elevated via replacement therapy, estradiol levels rise predictably as more substrate becomes available for the aromatase enzyme to process.

Clinical implications for aging

In older men, such as those in their 70s, the decline in testosterone production often results in a secondary decline in estradiol. Because estradiol plays a critical role in male health—particularly in maintaining bone mineral density and regulating fat mass—the reduction in testosterone can have broader metabolic and skeletal consequences due to this diminished estrogenic signal.

Bottom line

The claim is strongly supported by scientific evidence: approximately 80-85% of a man's estradiol is produced by the peripheral aromatization of testosterone, meaning that lower available testosterone levels naturally lead to lower estradiol production.