Where is sperm produced? 

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The sperm production cycle is called spermatogenesis. Spermatogenesis occurs inside testicles, in structures called seminiferous tubules. Seminiferous tubules contain specialized cells—called Sertoli cells—which directly support spermatogenesis. Another type of cell, the Leydig cells, sit outside the seminiferous tubules and produce the hormone testosterone, which is also required for sperm production and has other health effects throughout the body.ⁱ  

Every day, an adult male produces approximately 100 to 300 million sperm cells.^ii,iii,iv

Semen vs sperm  

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Sperm are the male reproductive cells that are produced in the testes and that fertilize the female egg. Semen is the fluid released during male ejaculation; it contains sperm as well as a cell-free fluid called seminal plasma or seminal fluid.

Several male reproductive organs secrete seminal fluid, including the seminal vesicles, prostate gland, bulbourethral (Cowper’s) glands, and epididymis.^v Seminal fluid is rich in substances that support the wellbeing of sperm cells, including fructose, prostaglandins, ascorbic acid (vitamin C), phosphatase, calcium, zinc, and magnesium.^vi,vii

Semen promotes healthy sperm and helps transport sperm so they can reach and fertilize an egg. Seminal fluid also stimulates a response in the female reproductive tract to promote conception and embryo implantation, thereby improving the chances of producing viable offspring.^viii

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How is sperm produced?

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Spermatogenesis occurs in the seminiferous tubules inside the testes, beginning with an immature sperm cell called a spermatogonial stem cell. Spermatogonial stem cells are located along the outside of the seminiferous tubules; as they develop into mature sperm cells, they move toward the inside of the tubules.^ix Spermatogonial stem cells undergo a cell division process called mitosis to form new specialized cells called primary spermatocyte cells. Like most human cells, primary spermatocytes are diploid cells.  

Primary spermatocytes then undergo a different type of cell division known as meiosis, which reduces the number of chromosomes within the spermatocytes by half. This is how sperm develop into haploid cells and become capable of fertilizing eggs (also haploid cells).

After meiosis, primary spermatocytes become spermatids. Spermatids have the correct number of chromosomes but are not yet mobile; they become mature sperm cells through a process called spermiogenesis. This process allows the spermatozoa to become motile and swim within semen, giving them the ability to reach and possibly fertilize the female egg.^x Spermiogenesis occurs in a structure called the epididymis, a long-coiled tube near the testicle that stores sperm prior to ejaculation. It takes sperm 2 to 11 days to mature within the epididymis.^xi

The entire process of spermatogenesis takes approximately 74 days.^xii

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How long does it take for sperm to refill?

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While it takes approximately 74 days for a single sperm cell to become fully mature, sperm production occurs continuously in the adult male, leading to the production of 100-300 million sperm cells per day. For this reason, a male’s sperm reserve may be temporarily decreased by ejaculation, but there is no long-term depletion because sperm is constantly being produced. ^xiii

A study by Mayorga-Torres et al (2015) investigated sperm count and sperm functional quality in men who gave daily samples of semen for two weeks, after a 3 to 4 day period of abstinence. They found that the total sperm counts and semen volume were lower during the daily ejaculation period, but observed no impact on sperm concentration, motility, morphology, and other quality parameters following the daily ejaculations.^xiv  

How long should one abstain from ejaculation before giving a semen sample?  

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The World Health Organization (WHO) recommends abstaining from ejaculation for at least two but no more than seven days prior to giving a semen sample.^xv There is conflicting data as to whether shorter or more extended abstinence can further improve semen parameters. For example, men with below average semen parameters may see improvement with more prolonged abstinence, while those with normal semen analyses may benefit from not abstaining more than 24 hours.^{xvi,xvii,xviii}

Those with known DNA fragmentation issues may also want to avoid longer abstinence before providing a sample. A study by Agarwal et al (2016) found that a shorter ejaculatory abstinence period of 1 to 2 days was associated with lower DNA fragmentation, resulting in healthier sperm that were more likely to fertilize an egg.^xix

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How is sperm health defined and tested? 

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Sperm health is defined by parameters measured in semen analysis, the main test for studying male infertility. Semen analysis is completed by collecting a sperm sample obtained through masturbation following an abstinence period of 2 to 7 days. The semen contents are then analyzed and the semen is evaluated under a microscope.^xx

Parameters measured on a semen analysis include semen volume, sperm concentration, total sperm number or sperm count, morphology, vitality, progressive motility, and total motility.  

The World Health Organization (WHO) developed reference ranges to help determine the ranges for normal sperm parameters. These ranges were based on a population of over 1 900 men (considered fertile men) in eight countries, with a time-to-pregnancy of less than one year.^xxi WHO determined the values for the 2.5^th to 97.5^th percentile for each of these parameters. The 5^th percentiles are commonly used as the lower limit for normal laboratory values, meaning that values below this would be considered low or abnormal:^xxii

^‍ Table 1. WHO Semen Parameters: 5th and 50th Percentile Values*

^{*Cooper, T. G., et al. (2009). World Health Organization reference values for human semen characteristics. Human Reproduction Update, 16(3), 231-245. https://doi.org/10.1093/humupd/dmp048}

The global decline of sperm count and male fertility is a contentious health topic in the 21^st century.  One 2017 systematic review of 185 studies showed that sperm concentration decreased by over 50 percent in Western countries during the period of 1973 to 2011.^xxiii

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What problems can there be with sperm?

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Certain health conditions can impact sperm production, with those impacts ranging from low sperm count to male infertility. Some of these conditions include:

• Klinefelter syndrome: a genetic condition in which a male is born with an extra copy of the X-chromosome
• Varicocele: an enlargement of the veins that transport blood away from the testicle
• Sperm DNA fragmentation: abnormal genetic material within some sperm cells that can result in male infertility
• Hypothyroidism: reduced thyroid function  
• Sperm delivery: ejaculation problems (e.g., erectile dysfunction, premature ejaculation, and retrograde ejaculation) usually do not affect the sperm themselves, but rather the delivery of the sperm to the egg in natural conception

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How to improve sperm health 

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A number of interventions are available to increase sperm production and promote normal sperm count, ranging from medications to lifestyle modifications.  

Clomiphene is a medication that can be prescribed to potentially improve sperm parameters and production. A study of infertile men found that clomiphene improved both sperm motility (from 59.7 to 90.9 million/ml) and sperm concentration (from 50.7 to 72.5 million/ml), although these values did not reach statistical significance.^xxiv  

A systematic review by Ahmadi et al (2016) observed that antioxidant supplementation can improve sperm parameters. Specifically, they found that supplementing with vitamin C, vitamin E, and Coenzyme Q10 improved sperm parameters in males.^xxv In another study of 690 men taking vitamin E in combination with selenium, 52.6 percent of the participants showed improvement in sperm motility, sperm morphology, or both.^xxvi

A 2021 study of 263 healthy men showed that the Mediterranean diet and increasing exercise improved sperm concentration, motility, and morphology.^xxvii The Mediterranean diet includes a high intake of vegetables, legumes, fruits, nuts, grains, fish, seafood, and olive oil.

Furthermore, diets rich in processed meat, soy foods, potatoes, full-fat dairy and total dairy products, cheese, coffee, alcohol, sugar-sweetened beverages and sweets have been associated with lower quality of semen in some studies. As far as fecundity is concerned, a high intake of alcohol, caffeine, red meat, and processed meat by men may also have a negative influence on the chance of pregnancy or fertilization rates in their partners.^xxviii The magnitude of dietary and lifestyle interventions on improving semen analysis parameters is not completely defined, and additional research is required to determine which factors are most likely to improve male fertility.

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Conclusion

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The production of sperm occurs throughout a biological male’s life, starting at puberty and continuing over his lifespan. This is in contrast to the production of eggs in women, who are born with all the eggs they will ever make and therefore have a more finite reserve.

Multiple factors can influence the production and health of sperm cells, including certain medical conditions and lifestyle factors. Men concerned with male fertility issues can work with their doctors to assess sperm health and implement strategies to improve it if needed.