Testosterone & Male Fertility

While taking testosterone can increase muscle mass and strength, it can also impair sperm production and contribute to male factor infertility.

Background

Testosterone is the principal androgen in males. Among its many functions, it supports muscle development and maintenance, bone health, libido, voice deepening during puberty, and normal reproductive function. Although testosterone is essential for sperm production, taking exogenous testosterone (testosterone from an external source) can disrupt the hormonal signals required for spermatogenesis.

Some men use testosterone to increase muscle mass or improve physical performance without realizing that it can suppress the body's natural production of reproductive hormones. As a result, a man may have a serum testosterone level of 900 ng/dL or higher while simultaneously experiencing a very low sperm count.

Introduction

To understand this apparent contradiction, we need to look beyond serum testosterone and examine the relationship between the hypothalamus, pituitary gland, supportive cells (Leydig cells and Sertoli cells), and intratesticular testosterone. The negative feedback mechanism that exists between all these “moving parts” is also crucial to fully understand how taking exogenous testosterone may negatively impact spermatogenesis.

The Moving Parts

The hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the anterior pituitary gland to release two important reproductive hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). In men, FSH stimulates Sertoli cells to perform several functions necessary for spermatogenesis, including production of androgen-binding protein (ABP), inhibin B, and various growth factors and nutrients that support developing germ cells (immature sperm cells). LH stimulates Leydig cells which are mainly tasked with the production of testosterone. Both hormones, FSH and LH, are crucial for healthy spermatogenesis. For example, if there is inadequate upstream stimulation (hypothalamus/pituitary) where FSH and LH are secreted below the normal range, the Sertoli and Leydig cells will not be able to function properly and spermatogenesis will suffer. In a different scenario, where FSH and LH are within normal range, spermatogenesis can still be negatively affected if the intratesticular environment (Sertoli cells, Leydig cells, seminiferous tubules, etc.) is not functioning properly (intratesticular dysfunction).

Testosterone Levels

Intratesticular testosterone is normally present at concentrations many times higher than those found in the bloodstream. According to a study published in 2024 by the Journal of Men’s Health, the levels of intratesticular testosterone are approximately 100 times higher than the corresponding serum testosterone levels. LH stimulates Leydig cells to produce testosterone within the testes, while androgen-binding protein (ABP), produced by Sertoli cells, helps maintain a high local concentration of testosterone near developing sperm cells. A man may have a normal or elevated serum testosterone level while producing very few sperm—or even no sperm—because serum testosterone does not necessarily reflect the testosterone concentration inside the testes.

The Negative Feedback Mechanism

Testosterone and FSH work together to maintain the environment required for spermatogenesis. There are two negative-feedback systems operating simultaneously:

LH stimulates Leydig cells to produce testosterone. When testosterone levels are sufficiently high, testosterone signals the hypothalamus to reduce GnRH secretion. When GnRH is reduced, LH is reduced. When LH is reduced, the Leydig cells don’t produce testosterone. Exogenous testosterone raises the serum testosterone level with the potential effect of signaling the the hypothalamus to reduce GnRH secretion.

FSH acts on Sertoli cells to support sperm development. Sertoli cells produce inhibin B, which provides negative feedback to the pituitary gland and helps regulate FSH secretion. When sperm-producing cell numbers grow, they release more inhibin B, which drops FSH levels. When inhibin B drops, FSH rises again.

What Can Men Do To Support Fertility

CoQ-10

While some meta-analyses show positive changes in hormone profiles, other individual clinical trials note that changes in testosterone levels may not always reach statistical significance. Even though CoQ-10 does not affect testosterone production directly, several studies agree that CoQ-10 can affect testosterone by protecting testicular cells from oxidative stress, which can impair hormone production.

Acupuncture

Used as a complementary therapy rather than a direct hormone replacement, acupuncture supports male testosterone levels by reducing stress, improving blood flow, and encouraging the body's natural endocrine function.Studies have shown that acupuncture could significantly reduce the level of FSH and LH in patients with oligoasthenospermia, which suggests that acupuncture may help reduce the damage of testicular seminiferous epithelium and mesenchymal cells caused by abnormal levels of FSH and LH, thereby improving male fertility. 

Conclusion

A high serum testosterone level does not necessarily mean that the testes are receiving the hormonal support needed for sperm production. Exogenous testosterone can suppress LH and FSH, reduce intratesticular testosterone, and impair spermatogenesis. Men who are planning to have children should discuss their treatment options with a qualified healthcare professional, because recovery of sperm production after testosterone use can vary from person to person.