Testes

Testes: Anatomy, Physiology, Health Assessment, and Nutritional Support

Overview and Definition

The testes are male sex glands that have both an endocrine and exocrine function. The testes are the male reproductive gonads of all bilaterians, including humans, and are homologous to female ovaries. Their function is to produce sperm and androgens, primarily testosterone. The function of the male, or testicular, reproductive system is to produce sperm and transfer them to the female reproductive tract. The paired testes are a crucial component in this process, as they produce both sperm and androgens, the hormones that support male reproductive physiology.

Anatomy and Structure

Gross Anatomy and Location

The testes are oval-shaped reproductive structures that are found in the scrotum and separated by the scrotal septum. They are bean-shaped, measuring 3 cm by 5 cm in length and 2 cm to 3 cm in width. The spermatic cord suspends the superior aspect of the testes. At the inferior end, the testes are attached to the scrotum by the scrotal ligament, which is a remnant of the gubernaculum. In general, the left testis is affixed slightly lower than the right testis.

The testes are located in a skin-covered, highly pigmented, muscular sack called the scrotum that extends from the body behind the penis. This location is important in sperm production, which occurs within the testes, and proceeds more efficiently when the testes are kept 2 to 4°C below core body temperature. The dartos muscle makes up the subcutaneous muscle layer of the scrotum. It continues internally to make up the scrotal septum, a wall that divides the scrotum into two compartments, each housing one testis. Descending from the internal oblique muscle of the abdominal wall are the two cremaster muscles, which cover each testis like a muscular net. By contracting simultaneously, the dartos and cremaster muscles can elevate the testes in cold weather, moving the testes closer to the body and decreasing the surface area of the scrotum to retain heat.

Layers and Coverings

The most superficial layer of the testis is a capsule made of dense fibrous connective tissue called the tunica albuginea, which perpendicularly gives rise to the septa that divide the tissue of the testis into lobules. The tunica albuginea thickens along the posterior surface of the testis and projects into it as the mediastinum testis, a connective tissue compartment through which all vessels and ducts of the testis pass on their way in or out. Fibrous septa extend from the mediastinum testis, creating the borders of the lobules which contain the seminiferous tubules. Inside the scrotum, the testes are covered almost entirely by the tunica vaginalis, a closed sac of parietal peritoneal origin that contains a small amount of viscous fluid.

Internal Architecture: Lobules and Seminiferous Tubules

Each testis is divided by partitions of fibrous tissue into 200 to 400 wedge-shaped sections, or lobes. Within each lobe are 3 to 10 coiled tubules, called seminiferous tubules, which produce the sperm cells. Each of the 200–300 lobules of the testis are filled with one to four highly convoluted seminiferous tubules which each course towards the mediastinum testis.

Sperm is produced in the seminiferous epithelium of the seminiferous tubules. The seminiferous epithelium mainly consists of spermatogenic and Sertoli cells. In vivo, the blood-testis barrier (BTB), in part comprised of tight junctions between adjacent somatic Sertoli cells, compartmentalizes meiotic spermatocytes and post-meiotic spermatids away from the vasculature, thereby preventing autoantibody production by the immune system against these immunogenic germ cells.

Key Cell Types

The testes contain germ cells that differentiate into mature spermatozoa, supporting cells called Sertoli cells, and testosterone-producing cells called Leydig (interstitial) cells.

• Leydig Cells: In the interstitial tissue lie the Leydig cells that are responsible for testosterone production. Between the seminiferous tubules is the interstitium, comprised of fluid and niches of cells. The interstitial cell niche contains the steroidogenic Leydig cells, responsible for testosterone production, and immune cells, which support numerous testicular functions.
• Sertoli Cells: The seminiferous tubules are lined by Sertoli cells that aid the maturation process of the spermatozoa. Testosterone that diffuses into Sertoli cells binds to the androgen receptor (AR) present in the cytoplasm and nucleus to initiate the functional responses required to support spermatogenesis.
• Germ Cells: Normal spermatogenesis is determined by the development of spermatogenic cells (including spermatogonia, primary spermatocytes, secondary spermatocytes, sperm cells, and sperm), function of Sertoli cells, and regulatory role of androgens.

Associated Structures: Epididymis and Ductwork

The epididymis is a small, curved, elongated structure that is highly convoluted and tightly compressed. When open in a straight line, its length is estimated at about 20 feet. The epididymis is found on the posterior border of the testis and consists of 3 parts, which include the head (caput), body (corpus), and tail (cauda). The developing sperm travels through the tubules, collecting in the rete testis. Ducts known as efferent tubules transport the sperm from the rete testis to the epididymis for storage and maturation. The epididymis stores sperm cells until they are mature and ready for ejaculation.

Vasculature and Innervation

The testes receive their primary blood supply from the paired testicular arteries, which branch off the abdominal aorta. Additional blood supply comes from the cremasteric artery and the artery of the vas deferens, creating anastomoses with the main arteries. The testes are suspended from the abdomen by the spermatic cord — a collection of vessels, nerves, and ducts that supply the testes.

Embryological Development and Descent

The embryonic differentiation of the primitive, indifferent gonad into either the testes or the ovaries is determined by the presence or absence of genes carried on the Y chromosome. The testes are formed in the abdominal cavity and descend into the scrotum during the seventh month of gestation, when they are stimulated by androgens. About 2 percent of newborn boys have an undescended testis at birth, but this condition often corrects itself by the age of three months.

Physiological Functions

Spermatogenesis (Exocrine Function)

Seminiferous tubules are coiled tubes that make up most of each testis. The cells and tissues in the tubules are responsible for spermatogenesis, which is the process of creating sperm. The division of spermatogonial stem cells (SSCs) along the basement membrane of the seminiferous tubule initiates the spermatogenesis process. The proliferation of SSCs results in either the production of two new stem cells to retain the stem cell pool or undifferentiated spermatogonia that are destined to develop into sperm.

Spermatogenesis and male fertility are dependent upon the presence of testosterone in the testis. In the absence of testosterone or the androgen receptor, spermatogenesis does not proceed beyond the meiosis stage. The maintenance of spermatogenesis in humans requires an adequate secretion of LH, resulting in the maintenance of high intra-testicular testosterone (ITT). Testosterone levels are approximately 40-fold higher in the testes than in the serum in healthy men with normal reproductive physiology.

Steroidogenesis: Testosterone Production (Endocrine Function)

Testosterone is the primary androgen in the male body, and its levels directly affect spermatogenesis. Testosterone is primarily synthesized and secreted by Leydig cells in the testes through a series of enzymatic reactions. The enzymes required for steroidogenesis are located in the mitochondria and in the endoplasmic reticulum, thus intracellular transport of substrates between these organelles is necessary for androgen production. Adult men typically produce around 7 mg testosterone daily but also produce lesser amounts of weaker androgens such as androstenedione and dehydroepiandrosterone. Testosterone is an important hormone during male development and maturation for developing muscles, deepening the voice, and growing body hair.

Additional Hormones Produced by the Testes

The testes also produce other hormones, such as inhibin, which helps regulate follicle-stimulating hormone (FSH) levels, and estrogen, albeit in small amounts. The testes also make inhibin B, which relates to testicular volume and the amount of sperm in the semen (sperm count); anti-Müllerian hormone, which is important to the development of internal reproductive organs; and insulin-like factor 3, which helps testicles descend into the scrotum from the abdomen.

The Hypothalamic–Pituitary–Testicular (HPT) Axis

The Hypothalamic–Pituitary–Testicular (HPT) Axis is the key axis to regulate spermatogenesis in males. It starts in the hypothalamus, which releases gonadotropin-releasing hormone (GnRH) in a pulsatile manner and which stimulates the anterior pituitary gland to release the gonadotropins — follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates the Sertoli cells in the testes through the FSH receptor and further stimulates spermatogenesis. LH acts on Leydig cells in the testes, which facilitates testosterone production. The regulation of testosterone levels is governed by the negative feedback mechanisms of the HPG axis, as well as local factors within the testes.

Health Assessment of the Testes

Clinical and Physical Examination

The evaluation of testicular function is based primarily on a detailed medical history, a careful physical examination, basal measurements of FSH, LH and testosterone, and a routine semen analysis. To verify testicular volume, ultrasound of the scrotum is performed. According to the most commonly accepted criterion in clinical practice, the hypotrophic gonad is considered when the volume of the testis is less than 12 mL.

Hormonal Laboratory Assessment

Since the symptoms of hypogonadism are nonspecific, and the signs of testosterone deficiency can be subtle and slow to develop, the assessment of testicular function relies heavily on laboratory testing. The laboratory diagnosis of hypogonadism is based on a consistent and unequivocally low serum total testosterone level measured in blood samples obtained in the morning. However, many men who present with adult-onset hypogonadism have a low total testosterone level due to a low level of sex hormone-binding globulin (SHBG) associated with obesity, insulin resistance, metabolic fatty liver disease, and type 2 diabetes, and may not be truly testosterone deficient. If testosterone deficiency is confirmed, the next step is to differentiate between primary and hypogonadotropic hypogonadism by measuring LH and FSH.

Semen Analysis

Semen analysis is conducted in accordance with the WHO Laboratory Manual for the Examination and Processing of Human Semen. Samples are collected after an abstinence period of 2–7 days and analyzed within 60 minutes of collection. Sperm function tests are often performed in patients presenting with infertility. These tests may help delineate the abnormality of the spermatozoa at each stage during the achievement of fertilizing capacity, such as adequate forward motility, penetration of cervical mucus, acrosome reaction, development of hyperactivated motility, binding to the zona pellucida, and fusion with the oocyte.

Factors Supporting Normal Testicular Function

The proper development of Leydig cells during puberty is essential for initiating spermatogenesis and promoting secondary sexual characteristics in males. The daily degree of testicular descent varies primarily according to temperature. This is controlled by the cremaster muscles. Testicular physiology comprises an intricate interrelationship involving various cell types, hormones, and signaling pathways, all of which play a crucial role in regulating spermatogenesis and hormone synthesis. It involves the coordinated functioning of various cells and hormones to maintain male reproductive health and fertility.

Associated Conditions and Diseases

Hypogonadism

Male hypogonadism occurs when the testicles cannot produce or produce insufficient sperm or male hormones, such as testosterone. Insufficient physiological concentration of testosterone leads to hypogonadism. With increment in age, there is a characteristic decrease in androgen generation and this may elicit hypogonadism particularly in elderly men. Hypogonadism can cause erectile dysfunction, decreased sex drive, and infertility. It can also cause decreased beard growth, enlarged breast tissue, and menopause-like symptoms including mood swings and hot flashes. Diseases that can affect the testicle, contributing to hypogonadism, include hemochromatosis, mumps, orchitis, testicular cancer, testicular torsion, and varicocele.

Varicocele

As many as one out of every five men has varicocele, which refers to swollen and dilated veins above the testicles (not unlike varicose veins), a condition that is usually benign. While surgery (varicocelectomy) often improves fertility, doctors are continually looking for ways to predict which patients will benefit most from the procedure. Scrotal color Doppler ultrasound is used to measure the intratesticular artery resistive index, which is an indicator of blood flow resistance and microvascular health.

Testicular Torsion

Testicular torsion means that the testicle has rotated in the scrotum. This can wind up the spermatic cord, cutting off blood supply, nerve function, and sperm transport to the scrotum.

Orchitis and Epididymitis

Orchitis refers to a swollen or inflamed testicle. Like epididymitis, orchitis often results from an infection caused by an STI. Both bacterial and viral infections can cause orchitis. More common than testicular cancer is epididymitis, which is inflammation of the epididymis. About 600,000 men develop it each year, most commonly between ages 19 and 35. Unprotected sex or having multiple sex partners increases the risk of infectious epididymitis.

Testicular Cancer

Testicular tumor is the most common malignancy in men of reproductive age. With cure rates as high as 90% and greater than 95% five-year survival rate, testicular cancer is one of the most curable malignancies. The etiology of testicular cancer is not well understood, but many risk factors — including cryptorchidism; inguinal hernia; contralateral testicular cancer; familial testicular cancer; testicular trauma; mumps orchitis; elevated testicular temperature; and hormonal, prenatal, and occupational factors — have been implicated in its development in young adults. The most established factor associated with testicular cancer is cryptorchidism, which is associated with a 2- to 4-fold increase in the risk of testicular cancer but accounts for fewer than 10% of all cases.

Male Infertility and Oxidative Stress

Oxidative stress is a significant factor in male infertility, compromising sperm function and overall reproductive health. Understanding testis physiology is crucial for diagnosing and treating male reproductive disorders and infertility. Any disruption in hormone production or spermatogenesis can lead to fertility issues, hormonal imbalances, and sexual dysfunctions.

Nutrients, Herbs, and Natural Ingredients

The following section categorizes ingredients by their traditional use and separately characterizes the available scientific evidence from human clinical and observational studies. Evidence strength is characterized honestly where studies are limited, preliminary, mixed, or animal/in-vitro only.

Zinc

Traditional Use: Zinc-rich foods (oysters, seeds, red meat) have been recognized in traditional dietary systems across multiple cultures as supporting male vitality and reproductive capacity, though formal ethnomedicinal zinc supplementation protocols were not a feature of historical herbal practice.

Scientific Evidence: Zinc serves as a cofactor for numerous metalloenzymes involved in DNA and protein synthesis, which are critically involved in germ cell development. Clinical studies with zinc-deprived adult males showed that testosterone synthesis and spermatogenesis were dependent on adequate dietary zinc supplementation. Maintaining optimal seminal plasma zinc levels is crucial, as low zinc levels are linked to impaired spermatogenesis and male infertility, while high zinc levels can cause oxidative stress and other changes that also contribute to infertility. Research into the impact of zinc levels in seminal plasma has shown that, although the results are not yet conclusive, altered (non-normal) zinc levels could influence semen parameters — particularly motility, morphology, and sperm count — and the level of the reproductive hormone testosterone. A systematic review and meta-analysis found that zinc and folic acid together, as well as multi-substance dietary supplements, improved sperm concentration. Evidence strength: Moderate. Zinc deficiency is clearly associated with impaired spermatogenesis; supplementation in deficient men shows benefit. Effects in replete men are less certain.

Vitamin D

Traditional Use: Vitamin D was not a recognized herbal or botanical ingredient in traditional medical systems; its role in testicular biology is a product of modern biochemical investigation.

Scientific Evidence: Vitamin D deficiency results in impaired reproductive performance in various species of animals, and the vitamin D receptor (VDR) along with activating and inactivating enzymes are expressed in the human testis, epididymis, seminal vesicle, prostate, and spermatozoa. Observational studies suggest an association between higher testosterone and serum vitamin D concentrations. Conversely, most randomized clinical trials that investigated the effect of vitamin D administration on testosterone levels have failed to detect any significant effect. A systematic review and meta-analysis concluded that vitamin D supplementation may improve sperm motility, progressive sperm motility, and morphology in infertile men. Mechanistically, vitamin D exhibits essential roles in the testis and prostate; otherwise, there is no apparent evidence to support the use of vitamin D supplementation to increase testosterone levels and to improve clinical outcomes related to the male reproductive system. Evidence strength: Weak to moderate for sperm parameters in deficient men. Not supported for testosterone elevation in vitamin D-replete men. Most RCT evidence does not confirm testosterone-boosting effects.

Coenzyme Q10 (CoQ10)

Traditional Use: CoQ10 has no documented traditional botanical use. Its investigation in male reproductive health is a product of modern nutraceutical research.

Scientific Evidence: A detailed examination of antioxidants including coenzyme Q10 alongside vitamin C, E, B12, D, zinc, folic acid, selenium, L-carnitine, L-arginine, inositols, and alpha-lipoic acid has been conducted in the context of oxidative stress and male infertility. A systematic review and meta-analysis found that coenzyme Q10 improved sperm motility in placebo-controlled trials. In a double-blind, placebo-controlled trial, 77 infertile men with a high DNA fragmentation index were randomized to receive a fertility supplement containing vitamins and antioxidants including 10 mg CoQ10 or placebo twice daily for 6 months. The antioxidant group had higher sperm density after 3 months compared to pre-treatment values, but no significant difference between antioxidant and placebo groups was seen for semen parameters or sperm DNA fragmentation index after treatment. Evidence strength: Preliminary to moderate. Meta-analyses suggest improvements in sperm motility; however, individual RCT results are inconsistent, and no confirmed effect on live-birth rates has been established.

Selenium

Traditional Use: Selenium was not formally identified as a dietary element until the 20th century and has no documented traditional botanical or herbal use specifically for testicular function.

Scientific Evidence: Zinc and selenium are considered essential in human testicular development and spermatogenesis. A systematic review and meta-analysis found that selenium improved sperm motility. Twenty-nine studies found a substantial positive effect of antioxidant supplementation on outcomes of assisted reproductive therapy, WHO semen parameters, and live-birth rate; carnitines, vitamin E and C, N-acetyl cysteine, coenzyme Q10, selenium, zinc, folic acid, and lycopene were among the beneficial antioxidants. Evidence strength: Moderate for sperm motility in infertile men. Studies are generally small and evidence quality is variable.

L-Carnitine and Acetyl-L-Carnitine

Traditional Use: L-Carnitine is an amino acid derivative with no documented traditional botanical use specifically for testicular or male reproductive health.

Scientific Evidence: The most frequently studied antioxidant supplementation doses in male infertility research have included carnitines (L-carnitine or L-acetyl-carnitine) at 500–1000 mg, alongside co-enzyme Q10 (100–300 mg), N-acetyl cysteine (600 mg), selenium (200 mg), and other antioxidants. Carnitine improved sperm motility in placebo-controlled randomized trials within a systematic review and meta-analysis. Evidence strength: Moderate for sperm motility improvements in infertile men. Evidence is consistent across multiple small RCTs but not confirmed in large, definitive trials.

Ashwagandha (Withania somnifera)

Traditional Use: From ancient times, Ashwagandha has been used by Ayurvedic practitioners as an aphrodisiac to improve on matters related to infertility and sexual activities. Ashwagandha is rich in a wide variety of chemical compounds, such as alkaloids, ergostane steroids, amino acids, and neurotransmitters, which explains its numerous medicinal properties. It is classified as a Rasayana (rejuvenating tonic) in Ayurvedic medicine and has been used for centuries across South Asian traditional medicine systems.

Scientific Evidence: Clinical trials and systematic reviews indicate that ashwagandha supplementation can significantly improve male fertility outcomes, particularly in men with oligospermia. In a randomized, placebo-controlled pilot study, men taking ashwagandha root extract for 90 days experienced a 167% increase in sperm count, a 53% increase in semen volume, and a 57% increase in sperm motility, along with improved reproductive hormone levels compared to placebo. In an 8-week prospective, double-blind, randomized, placebo-controlled study, improvements were observed in serum testosterone (p = 0.012), DHT, prolactin, FSH, and LH levels. A randomized crossover study on aged, overweight males showed that compared to placebo, ashwagandha supplementation was associated with 18% and 14.7% increases in DHEA-S and testosterone levels, respectively. Supplementation with ashwagandha showed positive findings in three out of four reviewed studies in terms of increases in testosterone levels. A systematic review reports that ashwagandha improves reproductive system function by enhancing semen quality, enhancing enzymatic activity in seminal plasma, and decreasing oxidative stress. Evidence strength: Moderate. Multiple small-to-medium RCTs in infertile or stressed men show consistent positive signals for sperm parameters and testosterone. Findings are more robust in sub-fertile or hypogonadal populations. Large, independent, high-quality RCTs are still needed.

Fenugreek (Trigonella foenum-graecum)

Traditional Use: Fenugreek has been used in Ayurvedic, traditional Chinese, and Middle Eastern medicine for centuries as a tonic herb and aphrodisiac. Its seeds were employed in preparations intended to enhance vitality and male reproductive capacity.

Scientific Evidence: Four out of six reviewed studies on fenugreek demonstrated significant increases in testosterone concentrations in humans. In summary, fenugreek is one of the most well-studied components of testosterone-booster products, and virtually all studies show increased testosterone levels in healthy adults, but further high-quality studies are warranted. Evidence strength: Moderate. Consistent signals for testosterone elevation across multiple RCTs, but most trials are small, industry-funded, or of short duration. Larger independent RCTs are needed to confirm effects and optimal dosing.

Tongkat Ali (Eurycoma longifolia)

Traditional Use: This plant, also known as Tongkat Ali, is known for its ability to stimulate the production of testosterone. It has been studied for its positive effects on libido, fertility, and sexual function, and has also been used traditionally to treat hypogonadism. It has a long history of use in Southeast Asian traditional medicine, particularly in Malaysia, Indonesia, and Thailand, where roots are prepared as decoctions or tonics.

Scientific Evidence: The effectiveness of this herb has been analyzed in several clinical studies. In a study involving 109 men with erectile dysfunction and low testosterone levels, taking Tongkat Ali for 12 weeks showed significant improvements in erectile function scores. Tongkat Ali, ashwagandha, and fenugreek were the substances with the strongest evidence among testosterone-booster ingredients reviewed in the published literature. A review found that out of 15 ingredients frequently used in testosterone-boosting supplements, only 3 showed the strongest evidence: Eurycoma longifolia (Tongkat Ali), ashwagandha, and fenugreek. Evidence strength: Moderate. Multiple RCTs show favorable effects on testosterone and sexual function, particularly in men with low or borderline testosterone. Most trials are small and further large-scale, independently conducted RCTs are required.

Tribulus Terrestris

Traditional Use: Tribulus terrestris has a history of use in Ayurvedic medicine in India and in traditional Chinese medicine, primarily as a tonic for urinary complaints, libido, and general vitality. It was also used in traditional Bulgarian and Turkish folk medicine.

Scientific Evidence: A 2025 systematic review of clinical trials concluded that Tribulus terrestris supplementation has a low level of evidence regarding its effectiveness in improving erectile function in men with erectile dysfunction, and no robust evidence was found for increasing testosterone levels. After searching the literature (n = 162), 52 studies were selected for full-text reading and 10 were eligible, comprising 9 clinical trials and 1 quasi-experimental study. The Jadad score revealed low methodological quality for 50% of the studies. Evidence strength: Weak. Current systematic review evidence does not support Tribulus terrestris as an effective testosterone-boosting agent in men. Most trials are small, short, and of low methodological quality.

Omega-3 Fatty Acids

Traditional Use: Omega-3-rich foods, particularly oily fish, have been part of traditional diets in coastal populations worldwide. While not specifically prescribed for testicular function in classical herbalism, these foods were broadly associated with virility and vitality in various traditional food cultures.

Scientific Evidence: Omega-3 fatty acids can improve some degree of sperm parameters in infertile men, alongside other natural agents such as zinc, vitamin D (in cases of hypovitaminosis D), L-arginine, mucuna, and ashwagandha. Evidence strength: Preliminary to moderate for sperm parameter improvement. The magnitude of effect and clinical significance for live birth rates remain unclear.

Antioxidant Combination Therapies (Vitamin C, Vitamin E, Folic Acid, Lycopene, N-Acetyl Cysteine)

Traditional Use: Individual components such as vitamin C (from citrus and other plants), vitamin E (from seeds and plant oils), and folic acid (from leafy greens) have been dietary staples in virtually all traditional food cultures, though their specific use for male reproductive health is a modern research focus.

Scientific Evidence: Antioxidants show notable potential in counteracting the negative effects of oxidative stress on sperm. Based on the evidence, these antioxidants, individually or synergistically, can enhance sperm health and reproductive outcomes. However, certain limitations in the studies call for careful interpretation. Twenty-nine studies found a substantial positive effect of antioxidant supplementation on outcomes of assisted reproductive therapy (ART), WHO semen parameters, and live-birth rate. Carnitines, vitamin E and C, N-acetyl cysteine, coenzyme Q10, selenium, zinc, folic acid, and lycopene were among the benefic antioxidants identified. Before implementing these nutraceutical agents, adequate sleep, exercise, and weight loss in patients with obesity are imperative. Evidence strength: Moderate overall for sperm parameter improvements in infertile men with elevated oxidative stress. Translation to improved live-birth rates is not yet consistently demonstrated. Most studies are small and heterogeneous in design.

References

• StatPearls – Anatomy, Abdomen and Pelvis: Testes (NCBI Bookshelf)
• Endotext – Endocrinology of the Testis and Spermatogenesis (NCBI Bookshelf)
• Endotext – Laboratory Assessment of Testicular Function (NCBI Bookshelf)
• OpenStax Anatomy and Physiology 2e – Chapter 27: Anatomy and Physiology of the Testicular Reproductive System
• TeachMeAnatomy – The Testes and Epididymis
• MDPI International Journal of Molecular Sciences – Hormone Regulation in Testicular Development and Function (2024)
• PMC / Frontiers in Endocrinology – The Role of Testosterone in Spermatogenesis: Proteome Profiling in Testosterone Deficiency (2022)
• PMC – The Regulation of Spermatogenesis by Androgens (2014)
• PMC – The effectiveness of zinc supplementation in men with isolated hypogonadotropic hypogonadism (2017)
• PubMed – Reviewing the Evidence on Vitamin D Supplementation in the Management of Testosterone Status (2020)
• PMC – Vitamin D supplementation for improving sperm parameters in infertile men: Systematic review and meta-analysis (2024)
• PMC – Coenzyme Q10 and Male Infertility: A Systematic Review (2021)
• PMC – Oxidative Stress and Male Infertility: The Protective Role of Antioxidants (2023)
• PMC – Antioxidant Supplementation on Male Fertility: A Systematic Review (2023)
• PMC – Association Between Zinc Levels and the Impact of Its Deficiency on Idiopathic Male Infertility (2025)
• PMC – Clinical Evaluation of Spermatogenic Activity of Ashwagandha Root Extract in Oligospermic Males: A Pilot Study (2013)
• PMC – Efficacy and Safety of Eight-Week Ashwagandha Root Extract in Improvement of Sexual Health in Healthy Men (2025)
• PMC – Withania somnifera (Ashwagandha) supplementation: mechanisms, health benefits, and role in sports performance (2025)
• PMC – Effects of Tribulus terrestris Supplementation on Erectile Dysfunction and Testosterone Levels in Men: A Systematic Review (2025)
• PMC – Insights into Supplements with Tribulus Terrestris used by Athletes (2014)
• PMC – The Effect of Dietary Supplements on Male Infertility in Terms of Pregnancy, Live Birth, and Sperm Parameters: Systematic Review and Meta-Analysis (2025)
• PubMed – A Randomized, Double-Blind, Placebo-Controlled, Crossover Study Examining Hormonal and Vitality Effects of Ashwagandha in Aging, Overweight Males (2019)
• PMC – Hypogonadism and Sexual Dysfunction in Testicular Tumor Survivors: A Systematic Review (2019)
• StatPearls – Testicular Cancer (NCBI Bookshelf)
• MedlinePlus – Male Hypogonadism
• Cleveland Clinic – Testicles (Testes): Location, Anatomy, Function and Conditions