Sperm production is a hormonal event. The testes do not simply decide to make sperm on their own. They wait for two signals from the pituitary gland, called follicle stimulating hormone (FSH) and luteinizing hormone (LH), and they need a high local concentration of testosterone. When any of those signals moves out of range, the result can show up as a low sperm count, poor motility, or abnormal shape. Hormonal imbalance is not one condition. It is a pattern of shifted signals, and the specific pattern determines which part of sperm production breaks down.
Men in many parts of the world are seeing lower sperm counts than earlier generations. A 2023 meta-analysis in Human Reproduction Update reported a 51.6% decline in global average sperm concentration from 1973 to 2018 (Levine et al.). Hormonal shifts are one recognized driver of that trend, though not the only one. This answer covers the main hormones involved in male fertility, what happens when each one is off, and what those patterns look like in practice.
The hormonal chain that makes sperm
The brain and testes run a feedback loop. The hypothalamus, a region at the base of the brain, releases gonadotropin releasing hormone (GnRH). GnRH tells the pituitary to release FSH and LH. LH travels to the Leydig cells in the testes and tells them to make testosterone. FSH travels to the Sertoli cells and tells them to support developing sperm. Testosterone and estradiol then feed back to the brain to dial the loop up or down. If testosterone stays too low for too long, or if the pituitary stops sending enough FSH or LH, sperm production slows.
This is the same axis that controls muscle, bone density, and sex drive, but inside the testes it runs at a different intensity. The testicular environment is designed to keep testosterone levels far higher than what circulates in the blood.
Testosterone: more than a blood test number
Inside the testes, testosterone concentration is much higher than in blood. That local concentration is what matures germ cells into sperm. A man can have low circulating testosterone and still be fertile if his testes are making enough local testosterone from LH stimulation. The reverse is also true. A man can have normal blood testosterone but poor sperm production if the problem exists inside the testicular environment itself.
Low testosterone, when it does reach the testes, reduces sperm count, motility, and normal morphology. Testosterone also maintains the epididymis, the coiled tube where sperm gain the ability to swim. Deficits can show up first as low libido, reduced erectile function, or reduced semen volume.
FSH and LH: the pituitary's two levers
FSH is the signal most directly tied to sperm count. It stimulates Sertoli cells to multiply and support germ cells. Low FSH can reduce the number of sperm produced. High FSH, in contrast, often indicates that the testes are underperforming and the pituitary is trying to compensate. This pattern appears after testicular injury, some infections, or certain genetic conditions.
LH drives testosterone production from Leydig cells. Low LH plus low testosterone points to a problem in the hypothalamus or pituitary, which can come from stress, poor sleep, undernutrition, or a pituitary issue. High LH plus low testosterone points to a problem inside the testes themselves. The pattern of FSH, LH, and testosterone together tells a doctor more than any single number.
Estradiol: balance matters in both directions
Men convert a portion of testosterone to estradiol using an enzyme called aromatase. Aromatase is present in many tissues, and body fat is one of the largest sources. Estradiol is not a waste product. It helps regulate bone density, libido, and sperm maturation in the epididymis. But too much estradiol suppresses the hypothalamus and pituitary, which lowers FSH and LH and reduces testosterone production. Excess body fat raises aromatase activity, which can push this feedback loop in the wrong direction. Very low estradiol has also been associated with reduced sperm parameters and sexual function in some studies.
Prolactin: the brake that should not be stuck on
Prolactin is the hormone best known for milk production, but men make it too. High prolactin suppresses GnRH, which lowers FSH, LH, and testosterone. The classic cause of high prolactin is a small benign pituitary tumor called a prolactinoma, but elevated prolactin can also follow thyroid disease, certain medications, or chronic stress. Men with high prolactin often report low libido, erectile issues, and sometimes a milky discharge from the nipple. The fertility effect is a secondary slowdown of the whole pituitary-testicular axis.
Thyroid hormones: systemic signals that reach the testes
Thyroid hormones influence metabolism in nearly every tissue, including the testes. Both an underactive thyroid and an overactive thyroid have been linked to abnormal sperm counts and motility in studies. Thyroid disease also shifts sex hormone binding globulin (SHBG), which changes the amount of testosterone that is free and active. Semen parameters often improve after thyroid function returns to normal, which makes thyroid testing a standard part of a male fertility workup in many clinics.
Cortisol: stress and the HPA axis
Chronic stress activates the hypothalamic pituitary adrenal (HPA) axis, which raises cortisol. Cortisol can suppress GnRH release, lowering LH and testosterone. Acute stress, like a hard workout or a bad day, does not appear to crash fertility by itself. The pattern that matters is chronic elevation, from months of poor sleep, constant work stress, or life strain. The human evidence on stress and semen quality is mixed, but the mechanism is well described. Chronically high cortisol can also increase abdominal fat, which raises aromatase and shifts the testosterone-estradiol balance further.
Insulin, body fat, and SHBG
Insulin resistance and excess visceral fat change the hormonal environment in three ways. First, fat tissue converts testosterone to estradiol through aromatase. Second, insulin resistance lowers SHBG, which changes total testosterone readings and can increase the rate at which free testosterone is cleared. Third, chronic low-grade inflammation from visceral fat can stress the testes directly and reduce sperm quality. In practical terms, a man with insulin resistance may have low total testosterone, high estradiol, low SHBG, and a sperm analysis that shows reduced concentration and motility.
Environmental endocrine disruptors
Some chemicals in plastics, pesticides, and personal care products can act as endocrine disruptors. They can bind to hormone receptors, block normal hormone action, or change hormone production. Bisphenol A (BPA) and certain phthalates are the most studied in men. A 2024 meta-analysis in Toxics reported associations between BPA exposure and poorer sperm concentration and motility (Lu et al.). A 2021 review in Frontiers in Endocrinology summarized how endocrine disrupting chemicals can interfere with male reproductive development and adult hormone function (Rodprasert, Toppari and Virtanen). These are associations in population studies, not proof that a specific exposure caused a specific man's infertility. The mechanism is real, but the individual dose is hard to measure.
Microplastics have also been detected in human testicular tissue and semen (Hu et al., Toxicological Sciences, 2024; Zhao et al., Science of the Total Environment, 2023). Their role in hormonal imbalance or fertility is still unknown, and no study has shown that clothing is the source of the particles found in those tissues.
Patterns worth discussing with a doctor
These signs do not prove a hormonal imbalance, but they are common reasons men get a hormone panel:
- Low libido that lasts for months
- Difficulty getting or keeping erections
- Reduced semen volume
- Unexplained fatigue
- Loss of muscle mass while gaining abdominal fat
- Breast tissue growth or nipple discharge
- Headaches or vision changes with sexual symptoms
- A couple trying for 12 months or more without pregnancy
A doctor may order total testosterone, free testosterone, SHBG, FSH, LH, estradiol, prolactin, thyroid stimulating hormone, fasting glucose, and HbA1c. The pattern across those values matters more than any single number.
What you can do about hormonal imbalance
Several daily factors influence the hormonal axis. Sleep is a consistent one. Chronic sleep restriction has been shown to lower testosterone in controlled studies. Body composition matters because fat tissue is an endocrine organ. Reducing excess visceral fat can lower aromatase activity and shift the testosterone-estradiol ratio. Managing chronic stress through training, sleep, and social time can lower cortisol burden. Reducing alcohol helps, especially in heavy drinkers, because alcohol can lower testosterone and increase estrogen conversion. Finally, reducing everyday exposure to BPA and phthalates is possible. Avoid heating food in plastic, reduce canned food consumption, and choose less processed personal care products.
Hormonal imbalance is usually detectable and often modifiable. The first step is measuring the right markers rather than guessing. If a man and his partner have been trying to conceive for a year without success, a fertility evaluation that includes a hormone panel is a reasonable next step. Most hormonal causes of male infertility are not permanent. The pituitary and testes respond to changes in body weight, stress, sleep, and medical treatment when a cause is identified.
This content is for educational purposes only and is not medical advice. Oakman products are designed for physical comfort and cooling; they make no claims about fertility, sperm quality, or hormone levels. Consult a healthcare professional for personalized advice.