Last Updated on April 26, 2026
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When we talk about male hormones and fertility, most people immediately think of testosterone, sperm count, and sexual function. These are not wrong, but there is also one important thing that is rarely mentioned. And that’s the thyroid gland.
It is well known that women are more likely than men to be affected by thyroid dysfunction. In a recently published ThyForLife blog article, we looked into why this is the case. This, along with the effect of thyroid dysfunction on the female reproductive system, has been an important subject of research over the years.
In this blog article, however, we’ll focus on how thyroid health affects male sex hormones and fertility, and what it means for men concerned about reproductive function.
What are the hormones involved in the male reproductive system?
Androgens are a group of steroid sex hormones often referred to as “male hormones,” with testosterone being the most well-known. They play a major role in the development and maintenance of male reproductive tissues and physical traits, but are also essential for overall health in both sexes.
In men, androgens influence libido, sperm production, muscle mass, bone density, metabolism, mood, and red blood cell production. Testosterone is produced primarily in the testes, with smaller contributions from the adrenal glands.
The production and regulation of these hormones are controlled by the brain through hormonal signals involving the hypothalamus and pituitary gland. The two main hormones involved in regulating testosterone and sperm production are luteinizing hormone (LH) and follicle-stimulating hormone (FSH), collectively known as gonadotropins. These hormones are released by the pituitary gland and act directly on the testes, stimulating testosterone production and supporting spermatogenesis (the process of sperm cell development). This hormone network, often referred to as the hypothalamic–pituitary–gonadal (HPG) axis, is highly sensitive to disruptions from other hormonal systems, including the thyroid.
What does the thyroid do?
The thyroid is a small butterfly-shaped organ at the base of the neck that produces hormones, primarily T4 (thyroxine) and T3 (triiodothyronine), that regulate metabolism, energy levels, and virtually every organ system, including the male reproductive system. TSH (thyroid-stimulating hormone) from the pituitary gland controls thyroid hormone production. This means that there is some level of interaction between the hypothalamic–pituitary–thyroid (HPT) axis and the HPG axis.
Your thyroid affects your fertility too
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Download ThyForLife for FreeHow do thyroid hormones interact with male reproductive physiology?
Interestingly, research has shown that the testes have thyroid hormone receptors. This means thyroid hormones have a direct role in testicular development, sperm formation, and maturation.
Here’s how thyroid hormones affect male reproductive physiology:
1. By modulating hormone production
As mentioned earlier, thyroid hormones interact with the HPG axis, which is the hormonal network that regulates sex hormone production. If thyroid function is abnormal, the signaling in this axis can become disrupted. For instance, low thyroid hormone levels can reduce the signals that control testosterone production, while high thyroid hormone levels can alter the balance between testosterone and other hormones, including estrogen.
2. Through the effects on Sertoli and Leydig cells
Leydig and Sertoli cells are among the several major cell types in the testes. LH stimulates testosterone production by Leydig cells in the testes, while FSH supports sperm development through its actions on Sertoli cells. In a review article published in the Journal of Endocrinological Investigation in 2023, the authors suggest that thyroid hormones could influence both cell types. This may possibly be through the thyroid’s effect on cellular function critical for sperm production and testosterone synthesis.
How exactly can male fertility be negatively impacted when thyroid function is off?
Effects of hyperthyroidism (Overactive thyroid)
- Reduced sperm quality
Hyperthyroidism has been strongly associated with poor semen qualities, such as reduced sperm count, lower sperm motility (movement), abnormal morphology (shape), and reduced ejaculate volume.
- Oxidative stress and DNA damage
Based on previous research findings as reviewed in a recent review article published in the Journal of Clinical Medicine Research in 2025, it’s been found that excess thyroid hormones promote oxidative stress that can damage sperm integrity and DNA, while thyroid deficiency affects energy metabolism and cellular protection systems in sperm cells.
- Hormonal imbalance and suppression
Sex hormone-binding globulin (SHBG), a liver protein that binds testosterone, increases in hyperthyroidism. This raises total testosterone levels but lowers free (bioavailable) testosterone, which is what tissues actually use.
Effects of hypothyroidism (Underactive thyroid)
- Poor sperm quality
Like hyperthyroidism, hypothyroidism is also commonly associated with abnormal sperm shape and quality. Research findings link low thyroid hormone levels to lower sperm count, poor motility, and abnormal morphology.
- Lower testosterone levels
Research suggests that low thyroid levels can impair Leydig and Sertoli cell function and may lead to decreased testosterone production.
- Issues with erection and ejaculation
According to a number of research studies and publications (including an Iranian study published in the Urology Journal in 2012 and a review article published in the Aging Male journal in 2024), hypothyroidism has been linked to erectile dysfunction and delayed ejaculation, which can further affect fertility.
How does all of this translate to real fertility outcomes for men? And when should men be tested?
To some extent, thyroid dysfunction is recognized as a contributing factor in some cases of male infertility, although it is relatively rare compared to other causes.
Clinical guidelines generally do not recommend routine thyroid screening for every man with infertility, except when there are suggestive symptoms or abnormal semen quality.
For instance, thyroid function tests may be recommended when:
- Semen abnormalities (such as low sperm count, poor motility, or abnormal morphology) are present.
- There are symptoms of thyroid dysfunction (such as fatigue, weight changes, sexual dysfunction, cold/heat sensitivity, or hair loss).
- Hormonal imbalances (low testosterone) don’t have clear causes.
Can fixing thyroid function improve fertility?
Yes, it’s worth noting that in many cases of true thyroid dysfunction, treatment can improve reproductive health. In other words, the negative fertility effects of thyroid dysfunction are reversible once thyroid hormone levels are brought into the normal range through medication or treatment.
- Treatment of hyperthyroidism
Treating excessive thyroid hormone production (with antithyroid medications, radioactive iodine, or rarely surgery) can stabilize hormonal balance and sperm features.
- Treatment of hypothyroidism
Thyroid hormone replacement (like levothyroxine) can often improve testosterone levels and sperm quality when low thyroid hormones are the underlying cause.
But it’s also worth noting that:
- Fertility recovery can take several months.
- Male fertility is complex. Thyroid dysfunction is rarely the only cause of infertility. Other factors (genetic, lifestyle, or structural) often coexist.
Key takeaways
- While thyroid disorders are a relatively uncommon cause of male infertility compared to other factors, they can have significant effects on testosterone activity, sperm health, and reproductive outcomes.
- Both hypothyroidism and hyperthyroidism have been associated with lower testosterone levels in some studies.
- Fertility effects are often reversible with proper thyroid treatment.
- Men with fertility issues and possible thyroid symptoms may be recommended a thyroid panel as part of their evaluation by their healthcare provider.
- If you’re experiencing fertility concerns, talk to your GP who may recommend talking to an endocrinologist or reproductive specialist who can evaluate your thyroid and other potential causes.
