FSH - Follicle Stimulating Hormone

Follicle stimulating hormone (FSH) is a hormone secreted by the anterior pituitary gland (a small endocrine gland in the base of the brain). Once secreted in men, it stimulates the testes to produce testosterone and sperm. Thus, FSH plays a vital role in the hormonal status and reproductive ability of men. Abnormal levels (levels that are too high or too low) may indicate either a problem with testicular function or hypothalamic/pituitary function.

The Hypothalamic-Pituitary-Testicular Axis

The anterior pituitary secretes follicle stimulating hormone in response to another hormone, gonadotropin-releasing hormone (GnRH), that is, in turn, secreted by the hypothalamus (another small endocrine gland in the base of the brain).^1,2

Testosterone levels control the secretion of GnRH. When T levels are low, the hypothalamus releases more GnRH, which increases FSH as well as luteinizing hormone (LH) secretion. This increase in FSH in turn increases T levels in a self-correcting feedback loop. When T levels are high, the hypothalamus release less GnRH. As a result, less FSH and LH are secreted, which decreases T levels. The entire system is known as the hypothalamic-pituitary-testicular axis. When working properly, this axis works to normalize testosterone secretion and sperm production

What Does Follicle Stimulating Hormone Do?

Although follicle stimulating hormone is often associated with the female reproductive cycle, it is actually essential to growth, physical development, pubertal processes, and reproduction in males. Specifically, it stimulates the maturation of sperm cells prior to them becoming functional. It also works with another reproductive hormone secreted by the anterior pituitary, luteinizing hormone (LH), in reproduction.

In addition to stimulating the maturation of sperm cells, it stimulates testicular growth and increases the production of androgen-binding proteins (ABPs) in Sertoli cells within the testes. These proteins bind testosterone, which allows for high testosterone levels near the sperm and is essential for normal sperm maturation.^3-5

FSH Levels

As mentioned above, follicle stimulating hormone plays a vital role in the hormonal and reproductive status of men. Most often in men, an FSH test may be used to determine the cause for infertility, to determine the cause for low testosterone, or to aid in the diagnosis of pituitary or hypothalamus disorders.

Normal FSH levels for an adult male should fall between 1.5 and 12.4 mIU/mL (mIU/ml = milli international units per milliliter). Several disease states are related to either increased or decreased levels. In general, levels progressively increase in aging males as testosterone levels concurrently decline.

High FSH Levels

High follicle stimulating hormone levels are often an indication of low or absent fertility or that the testicles are not functioning properly. Abnormal sexual characteristics are also common when levels are too high. High levels can be due to⁸:

• Damage to testicles caused by alcohol abuse, chemotherapy, or radiation
• Testicular failure
• Advancing age (male menopause)
• Treatment with certain hormones
• Certain tumors in the pituitary gland
• Congenital adrenal hyperplasia
• Lupus among other less common disorders⁹

With regard to T levels, if you have low testosterone and your FSH levels are high, the testes themselves may not be working properly. Ideally, high LH and FSH levels should tell your testicles to increase testosterone production. However, if T levels remain low while FSH levels are high, the problem likely lies with the testicles’ inability to produce testosterone.

Low FSH Levels

Low follicle stimulating hormone levels in men may mean glands within the brain (the pituitary gland or hypothalamus) are not working properly and do not produce normal amounts of some or all hormones. Disease states with low levels include hypothalamic suppression, hypopituitarism, hyperprolactinemia (often in seen a certain type of brain tumor of the pituitary gland and sometimes associated with vision changes), and sex hormone deficiency among others.⁸ Of note, low FSH levels also lead to low LH levels.

With regard to T levels, if you have low testosterone and your LH and FSH levels are low, the feedback loop in the hypothalamus/pituitary may not working properly. Ideally, low T levels should increase the secretion of GnRH and thus FSH. However, if follicle stimulating hormone levels remain low when T levels are low, the problem is likely due to functional problems with the hypothalamus/pituitary.

Supplementation

Supplementation is mainly used in females to increase fertility or to induce ovulation in women who have had a difficult time conceiving or during IVF (in vitro fertilization).¹⁰ For males with abnormal levels, the underlying problem should be treated directly. Research is also ongoing into the use receptor blockers as a therapy for a wide range of solid tumors.¹¹

Concluding Remarks

Overall, FSH is an essential component of the hormonal system that regulates growth, development, and sexual reproduction in males. It can be used as a marker with which to identify and monitor certain disease states and as a therapy for others.