Male Fertility: A Complete Evidence-Based Guide

Male fertility is a man's capacity to father a child, and in clinical terms it is measured chiefly through a semen analysis assessed against the World Health Organization 2021 (sixth edition) reference values for sperm concentration, motility and morphology. A male factor contributes to roughly half of all cases where a couple has difficulty conceiving — on its own in about one in five couples, and alongside a female factor in many more. Sperm quality often tracks with general health,¹⁸ and the evidence is encouraging: it responds to lifestyle, nutrition and time. This guide sets out what the science actually shows — the biology and the evidence apply wherever you live — drawing on World Health Organization, NHS, HFEA and NICE guidance, with UK-specific pathways flagged where they help.

If you have been trying for a baby for a while and are starting to wonder whether something is wrong, you are in the right place — and it is worth knowing from the outset that male-factor difficulty is common, usually treatable or improvable, and rarely anyone's fault. This guide is detailed, but you can read it in sections. Take what is useful now and come back for the rest.

What does the NHS say about male fertility?

The NHS frames fertility as a couple's issue rather than one partner's problem, and the data bear that out. Where the female partner is under 40, around 84% of couples will conceive within a year if they have regular unprotected sex, and around 92% within two years.^1,5 When conception does not happen in that window, the NHS advises that you and your partner are assessed together, because a cause is found on the male side roughly as often as on the female side.

Fertility problems affect about one in seven couples in the UK.¹ In around half of these couples, a problem with sperm or with the testicles is part of the picture.^2,9 The Human Fertilisation and Embryology Authority (HFEA), the UK's fertility regulator, lists male-factor infertility among the common reasons couples are referred for treatment such as IVF or ICSI, and records the cause of infertility — including male factor — in its annual treatment data.³

If you recognise yourselves in those numbers, take some comfort from them too: male-factor difficulty is one of the most common reasons couples seek help, and the referral routes in the UK are well established.

The reassuring part of the NHS framing is that "a problem with sperm" is not a single fixed diagnosis. It covers everything from a temporary dip after an illness or a stressful few months, to a treatable infection, to a varicocele that can sometimes be corrected. Many causes are reversible or improvable, and the body produces sperm continuously throughout adult life, so changes you make now can show up in a sample a few months later.

Understanding your semen analysis results

A semen analysis is the cornerstone test of male fertility. It measures the volume of the ejaculate and the number, movement and shape of the sperm within it, then compares each value against the WHO 2021 (sixth edition) reference values — the international gold standard laboratories now use. These reference values are not pass/fail marks. They are the fifth centile of results seen in men who fathered a child within 12 months, meaning 95% of recently fertile men sat at or above each figure. A result below a threshold lowers the odds but does not rule out conception,²⁰ and a result above it does not guarantee it.

The table below sets out the WHO 2021 lower reference limits verbatim.

Source: World Health Organization, WHO laboratory manual for the examination and processing of human semen, sixth edition, 2021.⁴

Two practical points matter when you read a report. First, sperm production fluctuates, so a single below-range result should always be repeated — the NHS and NICE recommend a confirmatory test, usually around three months later, before drawing conclusions.⁵ Second, morphology in particular sounds alarming when only 4% of sperm are "normal forms", but that figure is normal by design under the strict WHO criteria;¹⁶ it is not a sign that 96% of your sperm are defective.

If you and your partner have been through recurrent miscarriage or repeated unexplained IVF failure, some clinics offer a sperm DNA fragmentation test, which looks at damage to the genetic material inside the sperm rather than the standard count-and-movement measures. It sits outside the routine NHS work-up but can add useful information in specific circumstances — our guide to sperm DNA fragmentation explains when it is worth considering. A fuller walk-through of how to read each line of a standard report, and what the WHO 2021 values mean for your chances, is covered in our dedicated guide to your semen analysis results.

If your report flags low movement specifically, the parameter to focus on is progressive motility, and there are practical, evidence-based steps that can help — covered in our guide to improving sperm motility naturally.

What causes male fertility problems?

In a large share of men with reduced fertility — by various estimates somewhere around 30–50% — no clear single cause is found, but where a cause is identified, it usually falls into one of four groups: lifestyle factors, medical conditions, environmental exposures and age.^2,9 The encouraging theme across all four is that several are modifiable, and because sperm take roughly two to three months to develop, changes you make today affect the sperm you produce next season.

Lifestyle factors

Smoking, heavy alcohol intake, being significantly overweight, recreational drug use and chronic heat exposure to the testicles are all linked to poorer sperm parameters. These are the causes most within your control, and they are covered in detail in the lifestyle section below.

Medical causes

A varicocele — enlarged veins in the scrotum, found in around 15% of all men but more commonly in men with fertility problems — is one of the most common identifiable and correctable causes.²⁹ Infections of the reproductive tract, previous surgery or injury, undescended testicles in childhood, and certain genetic conditions can also affect sperm production or delivery. Past or present infections such as mumps orchitis or sexually transmitted infections can damage or temporarily impair sperm production, while blockages anywhere along the route from testicle to urethra — including after a vasectomy or hernia repair — can prevent sperm reaching the ejaculate even when production is normal. Genetic causes, such as Klinefelter syndrome or Y-chromosome microdeletions, are uncommon, but they are something your specialist will specifically look for if your sperm count is very low or absent.²⁵ A detailed UK-focused guide to varicocele, including when surgery is and is not recommended, is in preparation.

Hormonal causes

Sperm production depends on a hormonal chain running from the brain (the hypothalamus and pituitary) to the testicles, involving testosterone, follicle-stimulating hormone (FSH) and luteinising hormone (LH). When this signalling is disrupted, sperm production can fall. Notably, taking testosterone supplements or anabolic steroids suppresses your body's own sperm production — a frequently missed cause. Our dedicated hormones guide explores how the male hormonal system supports fertility — and what can disrupt it.

Age

Male fertility declines more gently than female fertility, but it is not immune to age. From around 40 — and more noticeably from the mid-40s — sperm motility and DNA integrity gradually decline, and the time to conception tends to lengthen even when the female partner is young. We cover the specific evidence on fathering a child after 40 separately.

For a plain-English overview of the most common problems and how they are diagnosed and treated, see Let's talk male infertility: understanding causes and finding treatment and 4 common male fertility problems and how to diagnose and treat them. If a low count is the specific concern, our guide to low sperm count: causes, tests and natural treatment goes deeper.

How does diet affect male fertility?

Diet shapes the environment in which sperm develop over their two-to-three-month maturation window, and the pattern of eating matters more than any single "superfood". The strongest evidence supports a Mediterranean-style, plant-forward diet — rich in vegetables, fruit, whole grains, nuts, legumes, fish and olive oil — which is consistently associated with better sperm parameters, while diets high in processed meat, refined carbohydrates, full-fat dairy and sugar-sweetened drinks tend to track with poorer results.^6,21

Two mechanisms explain most of this. The first is oxidative stress: sperm are unusually vulnerable to damage from reactive oxygen species because their cell membranes are rich in polyunsaturated fats and they carry few internal defences. Dietary antioxidants — vitamin C, vitamin E, selenium, zinc, lycopene and the carotenoids found in colourful produce — help neutralise that damage. The second is the fatty-acid supply: omega-3 fats are structural components of the sperm membrane, and higher intake of oily fish is linked to better motility and morphology.^6,7 In practical terms, the colourful produce and oily fish you eat now are supplying the raw materials for the sperm you will produce two to three months from now.

A few specifics come up often. There is no good evidence that moderate soy intake harms male fertility in humans, despite the persistent claims you may have seen online — we unpack the actual research in our guide to soy and its effects in males. Conversely, very high intakes of trans fats and processed foods, and heavy alcohol, are the dietary patterns most worth reducing.

You cannot out-supplement a poor diet, but you also do not need a perfect one. Aim for consistency rather than perfection: most fertility-supportive eating is simply unprocessed, varied and weighted towards plants and fish.

Which nutrients have evidence for male fertility support?

This is the section couples ask about most, and it is also where the most overblown marketing claims live, so it is worth being precise. In UK and EU law, only a small set of nutrients carry an authorised health claim for functions relevant to male fertility on the GB Nutrition and Health Claims Register.²⁶ Everything else — however promising the research — is supported by evidence but does not carry an authorised claim, and we say so plainly below. Food supplements are foods, not medicines, and no supplement treats infertility.

Nutrients with an authorised GB Register claim

The following authorised claims may be used only for a food that is at least a source of the named nutrient, per the GB Nutrition and Health Claims Register (wording fetched 10 June 2026):

• Zinc: "Zinc contributes to normal fertility and reproduction"; "Zinc contributes to the maintenance of normal testosterone levels in the blood"; "Zinc contributes to normal DNA synthesis". Zinc is concentrated in semen and is one of the best-evidenced minerals for male reproductive function. A dedicated evidence review is in preparation.
• Selenium: "Selenium contributes to normal spermatogenesis" (the formation of sperm). Selenium is incorporated into a protein structure in the sperm tail, which is one reason it is linked to motility. Our detailed selenium guide is in preparation.
• Vitamin B6: "Vitamin B6 contributes to the regulation of hormonal activity", relevant to the hormonal signalling that underpins sperm production.
• Folate: "Folate contributes to maternal tissue growth during pregnancy". This is a pregnancy-facing (female) claim rather than a male-specific one; it is included because conception is a couple's project and folate status is part of preconception nutrition for the partnership. Folate's role in male fertility specifically is research-supported but not an authorised male claim — see our guide to folic acid and fertility.
• Vitamin D: "Vitamin D has a role in the process of cell division". This is an indirect, supporting claim only; the direct evidence for vitamin D and sperm outcomes is mixed, and we treat it as supportive rather than primary.

Nutrients with research support but no authorised male-fertility claim

The following are studied in male fertility and have promising evidence, but they do not carry an authorised GB Register claim for male fertility. We present them honestly as research-supported only, never as authorised-claim ingredients:

• Coenzyme Q10 (CoQ10): an antioxidant involved in cellular energy production, studied for motility; see our guide to what CoQ10 does for fertility.
• L-carnitine: involved in sperm energy metabolism, studied for motility and concentration; see L-carnitine for fertility.
• L-arginine: an amino acid studied for its role in sperm production, with mixed results.
• Vitamin E: an antioxidant studied alongside selenium and other nutrients; see vitamin E for fertility.

The honest summary is that combination antioxidant supplements show modest, inconsistent benefits for sperm parameters in trials, and the most recent Cochrane review found only low- to very low-certainty evidence of a possible benefit, so the effect on the outcome that matters most — a live birth — remains uncertain.^8,19,28 The largest UK and US randomised trials are instructive here: the FAZST trial, which tested folic acid and zinc in men whose partners were undergoing fertility treatment, found no improvement in semen quality or live-birth rates from that specific combination.²⁷ This does not mean nutrients are irrelevant — if you are genuinely deficient in zinc or selenium, you are a different case from a man who already has adequate intake — but it is a useful corrective to the idea that more is always better. Supplements are best seen as one supporting input alongside your diet, weight, smoking and alcohol, not a substitute for addressing them.

A word on safety and dosing. The nutrients above are safe at sensible food-supplement levels, but more is not better: very high zinc intakes over time can impair copper absorption, and several "fertility booster" products on the market combine large doses that have no added benefit and some risk. If you take other medicines or have a medical condition, check with a pharmacist or GP before starting a supplement, and treat any product promising to "cure", "treat" or "dramatically increase" your count with scepticism — that wording is not permitted for a food supplement in the UK.

If you want to see how FertilitySmart Conceive for Men compares ingredient-by-ingredient with other UK male fertility supplements, our comparison guides set out the formulations side by side.

Lifestyle and male fertility

If you do only a handful of things, do these. Lifestyle factors are the most modifiable causes of reduced sperm quality, and because each new batch of sperm takes around two to three months to mature, sustained changes typically show up in a semen analysis within a single season.

• Reach and hold a healthy weight: Obesity is associated with altered reproductive hormone levels and poorer sperm parameters;¹¹ losing excess weight is one of the better-evidenced ways to improve your parameters.
• Stop smoking: Smoking is consistently linked to lower count, motility and morphology, and to increased sperm DNA damage.^12,14 Stopping reverses much of the effect over time, and NHS Stop Smoking Services are free if you want support.
• Keep your alcohol within the UK low-risk guideline of no more than 14 units a week, spread over several days. Heavy drinking impairs semen quality;¹³ our guide to alcohol and fertility covers the evidence in full.
• Protect your testicles from excess heat: Sperm production works best slightly below core body temperature. Frequent hot baths, saunas, prolonged laptop use on the lap and very tight underwear can raise scrotal temperature;¹⁵ we cover the practical evidence on heat exposure separately.
• Exercise — but moderately: Regular moderate activity supports fertility, while extreme endurance training and anabolic steroid use can harm it. Our guide to exercise and fertility sets out a sensible balance.
• Prioritise sleep and manage stress: Poor and irregular sleep is linked to lower testosterone and sperm quality; see sleep and fertility. Chronic stress affects the same hormonal axis that governs your sperm production.

None of these requires perfection. The men who see the biggest gains are usually those who change two or three things and hold them steady for a few months, not those who chase an ideal for a fortnight.

When should you see a GP about fertility?

The NHS guidance is clear and worth knowing precisely. See your GP if you have not conceived after one year of regular unprotected sex (every two to three days).^1,5,22 Seek advice sooner — at around six months — if the female partner is aged 36 or over, or straight away if there is a known reason for concern on either side, such as previous testicular surgery, undescended testicles, chemotherapy, a very low sperm count on a previous test, or problems with erections or ejaculation.

NICE guideline NG257, published in March 2026 to replace the earlier CG156, is the authoritative UK guideline on fertility assessment and treatment. It recommends that both partners be seen together and that initial investigation begin in primary care rather than waiting for a specialist referral.⁵ For the man, that initial work-up is straightforward and starts with a semen analysis and a conversation about medical history and lifestyle.

It helps to understand who does what. A GP carries out the first assessment and arranges the initial semen analysis. Depending on the results, you may be referred to a urologist (a surgeon specialising in the male reproductive and urinary tract, who handles issues such as varicocele or blockages) or to a fertility clinic or reproductive medicine specialist (who coordinates couple-level treatment such as IUI, IVF or ICSI). A detailed comparison of NHS and private male fertility testing routes is in preparation.

There is no advantage in waiting beyond these thresholds. Earlier assessment widens your options, and many men are reassured to find the first step is a simple test rather than anything invasive.

What does an NHS-funded fertility investigation involve?

The male investigation is deliberately simple at first. It begins with a semen analysis, repeated to confirm any abnormal result, and a clinical history and examination. If the semen analysis is abnormal or there are other indications, the next steps may include blood tests to measure reproductive hormones (testosterone, FSH and LH), screening for infection, and sometimes a scrotal ultrasound to look for a varicocele or other structural issue. Genetic testing is reserved for specific situations such as a very low or absent sperm count.^5,23

What couples most need to understand about the NHS route is that funding for treatment varies by area. While NICE NG257 recommends up to three full IVF cycles for eligible women under 40 — and now allows up to three further cycles to be considered where the first three are unsuccessful⁵ — the actual number of funded cycles, and the eligibility criteria attached to them, are set locally by Integrated Care Boards and differ considerably across England; Scotland, Wales and Northern Ireland set their own policies. This is the single biggest source of frustration and surprise, so it is worth asking your GP or clinic early what is funded in your area.

Where NHS waiting times are long, or local criteria exclude you, private testing is widely available — a private semen analysis is relatively inexpensive and quick, and many couples use one to get an early read while NHS processes run in parallel. The NHS and private routes are not mutually exclusive, and using a private test to inform earlier lifestyle changes is a reasonable, low-cost step.

It is also worth setting expectations about timing. Sperm parameters are a snapshot of a process that took the previous three months, so if your first test is abnormal the most useful thing you can do while waiting for the repeat is to address the modifiable factors covered above. By the time the confirmatory analysis comes around — typically about three months later — any changes you have made will be reflected in the result. Couples sometimes find that the waiting period, used well, becomes the intervention rather than dead time.

Frequently Asked Questions

How long does it take for sperm to "refresh"?

The cycle that produces a new sperm cell — spermatogenesis — takes roughly 74 days, and with the extra time sperm spend maturing as they pass through the epididymis, the whole process comes to around three months. This is why lifestyle and nutrition changes need around three months to show up in your semen analysis, and why fertility specialists suggest starting any changes at least three months before you start trying to conceive.

Does cycling cause infertility?

For most men, recreational cycling does not harm fertility. The concern relates to very high-volume cycling combined with prolonged pressure and heat on the perineum and scrotum. If you cycle intensively, a well-fitted saddle, regular breaks and avoiding very long daily sessions are sensible precautions, but moderate cycling is not a recognised cause of infertility.

Does masturbation reduce sperm count?

No. Masturbation does not cause infertility or permanently lower your sperm count. Frequent ejaculation temporarily reduces the number of sperm in a single sample, which is why clinics ask for two to seven days of abstinence before a semen analysis, but the testes continuously produce new sperm and counts recover quickly.

Can age affect male fertility?

Yes, though more gradually than in women. From around 40, and more noticeably from the mid-40s, sperm motility and DNA integrity tend to decline, time to conception can lengthen, and there is a modest rise in certain risks. Men remain fertile far later than women on average, but age is a real, if gentle, factor.

Is male fertility declining in the UK?

Several large analyses report that average sperm counts in Western countries fell over the second half of the twentieth century and into the twenty-first.^10,17 The findings are debated on methodological grounds, and what they mean for any individual man is limited, but the trend has prompted legitimate research interest in environmental and lifestyle drivers.

Are fertility supplements regulated?

In the UK, fertility supplements are regulated as foods, not medicines. They must be safe, accurately labelled, and may only carry health claims that appear on the GB Nutrition and Health Claims Register, using the authorised wording. They are not licensed to treat or cure infertility, and any product claiming to do so is making an unlawful claim.

Can a man with a low sperm count still conceive naturally?

Yes. A below-reference result lowers the monthly odds but does not mean conception is impossible. Many men with low counts conceive naturally, sometimes after addressing a treatable cause or making lifestyle changes,²⁰ and assisted techniques such as IUI, IVF and especially ICSI are designed to work even with very low counts.²⁴

What is the single most effective thing I can do?

There is no universal answer, but for most men the highest-yield steps are stopping smoking, reaching a healthy weight, and moderating alcohol — sustained over at least three months. If your tests find a specific cause such as a varicocele or a hormonal issue, addressing that can matter more.

Do tight underwear and laptops really matter?

The effect of scrotal heat on sperm is real but usually modest. If your semen analysis is borderline, reducing heat exposure — looser underwear, fewer hot baths and saunas, not resting a laptop on your lap for hours — is an easy, no-downside change. For men with normal results it is unlikely to make a noticeable difference.

How accurate is a single semen analysis?

Not accurate enough to rely on alone. Sperm parameters vary naturally from week to week, so guidelines recommend confirming any abnormal result with a repeat test, usually around three months later. Any decision about your fertility should rest on at least two samples, not one.

Supporting Your Fertility with FertilitySmart

Supporting male fertility is rarely about one dramatic change — it is the steady combination of a varied, plant-forward diet, a healthy weight, less alcohol, no smoking and the right nutrients, held together over a few months while your body produces fresh sperm.

At FertilitySmart, we offer fertility supplements for both partners — Conceive for Men, formulated with zinc and selenium for their role in normal fertility and reproduction, and Conceive for Women. Explore our range of evidence-based fertility supplements formulated with the nutrients discussed in this guide.

Citations

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2. NHS. Infertility – Causes. National Health Service; 2023. nhs.uk/conditions/infertility/causes
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4. World Health Organization. WHO laboratory manual for the examination and processing of human semen. 6th ed. Geneva: WHO; 2021. who.int/publications/i/item/9789240030787
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24. Human Fertilisation and Embryology Authority. Intracytoplasmic sperm injection (ICSI). HFEA; accessed 11 June 2026. hfea.gov.uk/treatments/explore-all-treatments/intracytoplasmic-sperm-injection-icsi
25. Tüttelmann F, Ruckert C, Röpke A. Disorders of spermatogenesis: perspectives for novel genetic diagnostics. Medizinische Genetik. 2018;30(1):12–20. doi.org/10.1007/s11825-018-0181-7
26. GB Nutrition and Health Claims Register (retained Regulation (EC) No 1924/2006 as implemented by Commission Regulation (EU) No 432/2012). Department of Health and Social Care; accessed 10 June 2026. gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register
27. Schisterman EF, Sjaarda LA, Clemons T, et al. Effect of folic acid and zinc supplementation in men on semen quality and live birth (FAZST). JAMA. 2020;323(1):35–48. doi.org/10.1001/jama.2019.18714
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Marina Carter

Fertility Health Writer at FertilitySmart

Marina Carter is a specialist health writer with nearly a decade of experience in reproductive health, fertility nutrition, and evidence-based conception support. She has authored over 30 in-depth articles for FertilitySmart, translating peer-reviewed research into clear, practical guidance for individuals and couples trying to conceive. Read Full Bio →