Sperm Count: What Lowers It, What Raises It, and the 74-Day Rule

He was 34 and they had been trying for fourteen months. His partner had been through every test going. When his turn finally came, the semen analysis showed 11 million sperm per millilitre, below the reference limit.

His testosterone was 19 nmol/L. Comfortably normal. "How can my hormones be fine and my sperm be bad?" he asked, and nobody gave him a clear answer.

So he did everything at once. Stopped drinking, bought a zinc supplement, swapped his briefs for boxers, moved his laptop to a desk. Three weeks later he paid for a repeat test. Almost no change. He decided none of it worked and went back to how things were.

He had done several of the right things. He had just checked far too early, because the sperm in that second sample had started forming before he changed anything.

Sperm and testosterone are not the same thing

This is the first misunderstanding worth clearing up. Men assume a good testosterone result means good fertility, and a poor sperm count must mean low testosterone. Neither follows.

Sperm production depends on testosterone made inside the testes, at concentrations far higher than anything in your bloodstream. A blood test measures what spills out into circulation, not what is happening where sperm are made. Plenty of men with normal blood testosterone have poor semen results, and some men with low testosterone are perfectly fertile.

The more dangerous version of this confusion runs the other way. A man with borderline testosterone and a low sperm count is sometimes offered testosterone therapy. That is close to the worst thing he could take, because testosterone from outside tells the brain to stop sending the signals that drive sperm production. We cover exactly why in will TRT make you infertile, and the alternatives that protect fertility are explained in enclomiphene, Clomid and SERMs.

The 74-day rule

A sperm cell is not made overnight. It starts as a stem cell in the wall of the seminiferous tubules and goes through a long series of divisions and changes before it is released.

The figure you will see quoted most often is about 74 days. It comes from classic work in the 1960s by Heller and Clermont, who used radioactive labelling to time the process in men. Some later estimates are a little shorter, and after release the sperm spend roughly another one to two weeks maturing in the epididymis before they can be ejaculated.

The practical translation is simple: the sample you produce today reflects what you were doing two to three months ago.

This cuts both ways. A change you make now will not show up in a test for around three months. And something harmful that happened recently, a high fever, a course of anabolic steroids, a bad month of heavy drinking, may not show up yet either, then appear later when you thought you had recovered.

It is also why guidelines ask for a repeat test rather than trusting a single abnormal result. NICE recommends that a confirmatory semen analysis is done three months after an initial abnormal one, unless the first result is severely abnormal, in which case it should be repeated as soon as possible.

What counts as normal

Semen results are compared with reference limits published by the World Health Organization. In the 2021 edition, the lower reference limits include a concentration of 16 million sperm per millilitre, a total of 39 million per ejaculate, 42 per cent total motility, 30 per cent progressive motility and 4 per cent normal forms. The previous 2010 edition used 15 million per millilitre for concentration, which is why you will still see that figure quoted.

Two things about these numbers are widely misunderstood.

First, they are not pass marks. They describe the bottom 5 per cent of men whose partners conceived within a year. A man below them is not sterile, and a man above them is not guaranteed anything.

Second, one sample tells you surprisingly little. Semen results swing a great deal from week to week in the same man, affected by abstinence time, recent illness, how the sample was collected and how quickly it reached the lab. That is the reason for the repeat.

Is everyone's count falling?

Probably, though the size is debated. The largest analysis, published in 2023 by Levine and colleagues, pooled 288 estimates from samples collected between 1973 and 2018. It found sperm concentration fell by about 51.6 per cent over that period, and the rate of decline per year roughly doubled after 2000, from 1.16 per cent to 2.64 per cent.

Critics point out that counting methods changed over those decades and that the men studied are not identical groups. Even so, the pattern has held across repeated analyses, and it runs alongside the fall in testosterone we describe in why testosterone is falling across generations.

What lowers sperm count

Some causes are medical and need a doctor. Others are habits, and those are the ones you control. Roughly in order of how strong the evidence is:

1. Testosterone and anabolic steroids

This is the single biggest avoidable cause. Testosterone therapy, steroid cycles and many SARMs can reduce sperm production to zero. Recovery after stopping is usual but can take many months, and in some men it is incomplete. If you have ever used them, say so when you are tested. The road back is covered in testosterone recovery after steroids.

2. Heat

The testes sit outside the body for a reason. They work best a few degrees below core body temperature, and sustained warming reduces sperm production.

Two everyday examples have been measured. In a 2005 study by Sheynkin and colleagues, 29 young men sat for an hour with their thighs together, the position needed to balance a laptop. Scrotal temperature rose by 2.1°C with no laptop at all, and by 2.6 to 2.8°C with a working laptop on their knees.

Underwear has been studied too. In 656 men attending a fertility centre, those who mainly wore boxers had 25 per cent higher sperm concentration and 17 per cent higher total count than men who wore tighter styles, and 14 per cent lower FSH, a sign the brain was not having to push as hard. This is an association, not proof, but it is a cheap change.

Saunas, hot tubs and long hot baths belong in the same category. In a small study by Garolla and colleagues, 10 men who took two 15-minute sauna sessions a week for three months saw their sperm count and motility fall. Counts were still low three months after they stopped and back to normal at six months. If you are trying to conceive, regular sauna use is worth pausing.

3. Smoking

A 2016 meta-analysis in European Urology found that smokers had lower sperm counts, poorer motility and more abnormally shaped sperm, and the effect was stronger in moderate and heavy smokers. Stopping is one of the few changes with a clear direction of benefit and no downside.

4. Excess body fat

A pooled analysis by Sermondade and colleagues found that men who were overweight or obese were more likely to have a low sperm count or no sperm at all, and the risk climbed with each step up in body mass index. Fat tissue converts testosterone into oestrogen, which dampens the signal from the brain, and it raises scrotal temperature too. The mechanics are explained in stubborn belly fat in men.

5. Cannabis

In 1,215 young Danish men, those who used cannabis more than once a week had 28 per cent lower sperm concentration and 29 per cent lower total count. The picture is not uniform, and we go through the conflicting studies in does cannabis lower testosterone.

6. Heavy drinking

Occasional drinking has little measurable effect in most studies. Regular heavy drinking is a different matter, affecting both hormones and sperm. Where the line sits is covered in the truth about alcohol and testosterone.

7. Medical causes

A varicocele, a swelling of the veins above the testicle, is found in a large share of men with fertility problems and is one of the few causes that can be surgically repaired. Genetic conditions such as Klinefelter syndrome, past mumps affecting the testes, undescended testes in childhood, and some cancer treatments also matter. These need investigation, not lifestyle changes.

8. Chemical exposures

Observational studies link some plastics chemicals, particularly phthalates, to poorer semen quality. The evidence is weaker than for the causes above, but reducing exposure is simple: less food heated in plastic, fewer heavily fragranced products. More in our hormone disruptors guide.

What actually raises it

The honest answer is less exciting than the supplement industry would like. The most reliable way to improve sperm count is to remove whatever is harming it, then wait.

Remove the cause, then give it three months

Stop smoking. Take the laptop off your lap. Pause the daily sauna. Drop the cannabis. Cut heavy drinking. If you are carrying a lot of weight around the middle, losing some of it helps both hormones and heat. Then leave at least three months before retesting, because that is how long the new sperm take to arrive.

Walnuts, surprisingly

One of the better food trials is also one of the least glamorous. In 2012, Robbins and colleagues randomised 117 healthy men aged 21 to 35 either to add 75 g of walnuts a day to their usual Western-style diet or to avoid tree nuts. After 12 weeks, the walnut group had better sperm vitality, motility and morphology.

These were healthy men, not men with fertility problems, so the result should not be stretched too far. But 75 g of walnuts is a handful and a half, and it is a food, not a pill.

The supplement trials that did not work

This is the part most fertility supplement marketing leaves out.

In 2020, the largest trial of its kind, published in JAMA, gave 2,370 couples' male partners either 5 mg of folic acid plus 30 mg of zinc daily for six months, or a placebo. Semen quality did not improve. Live birth rates were 34 per cent with the supplement and 35 per cent with placebo. The supplement group actually showed a small increase in sperm DNA fragmentation.

The same year, the MOXI trial gave men with abnormal semen results a combination antioxidant containing vitamins C and E, selenium, L-carnitine, zinc, folic acid and lycopene. After three months, semen parameters and DNA integrity were no better than placebo, and live birth rates were 15 per cent in the antioxidant group against 24 per cent on placebo.

That does not prove no supplement could ever help anyone. A man who is genuinely deficient in zinc or folate is a different case. But the evidence does not support buying a fertility blend on the assumption that it will move the numbers. Our guides to zinc and supplements that waste your money go into this in more detail.

Food, broadly

Beyond walnuts, the evidence points in a familiar direction: diets built on fish, vegetables, whole grains, nuts and legumes tend to go with better semen quality than diets heavy in processed meat and sugary drinks. That is observational, but it lines up with everything else. Our lists of testosterone-friendly foods and foods that work against you are a sensible starting point, and oily fish such as salmon and sardines earn their place.

When to get tested, and what to ask for

NICE advises that couples who have not conceived after a year of regular unprotected sex should be offered investigation, and earlier if the woman is 36 or over or there is a known reason to worry. That includes a semen analysis for the man, not just tests for his partner.

If the semen analysis is abnormal, a blood test for testosterone, LH and FSH helps work out where the problem sits. A high FSH suggests the testes themselves are struggling. A low FSH with low testosterone points towards the brain's signal, which has different causes and different treatments. Our guides to the testosterone blood test and how to read blood test results explain what each marker means.

If you have ever used testosterone, steroids or SARMs, had a testicular injury or surgery, or had undescended testes as a child, do not wait a year. Ask sooner.

Common questions

How long does it take to improve sperm count?

At least three months, because that is roughly how long sperm take to form and mature. Testing earlier mostly measures sperm that were already on their way before you made changes.

Can low testosterone cause a low sperm count?

It can, but the two often move separately. Many men with normal blood testosterone have poor semen results, because sperm depend on testosterone inside the testes rather than in the blood.

Will a testosterone booster help my sperm?

There is no good evidence that over-the-counter boosters improve sperm. The largest supplement trials, including zinc with folic acid and a multi-antioxidant blend, found no improvement in semen quality or live births.

Is one bad semen test enough to know?

No. Results vary a lot within the same man. NICE recommends a repeat test three months after an abnormal result, or sooner if the result is severely abnormal.

Does taking TRT affect fertility?

Yes, significantly. External testosterone switches off the signals that drive sperm production and can reduce the count to zero. It is usually reversible after stopping, but recovery can take many months.

Do boxers really make a difference?

In one large study, men who mainly wore boxers had higher sperm concentration and total count than men in tighter underwear. It shows an association rather than proof, but it costs almost nothing to change.

Sources: Heller CG, Clermont Y, Spermatogenesis in man: an estimate of its duration, Science 1963;140(3563):184-6 · Levine H et al., Temporal trends in sperm count, Hum Reprod Update 2023;29(2):157-76 · World Health Organization, WHO laboratory manual for the examination and processing of human semen, 6th ed. 2021 · National Institute for Health and Care Excellence, Fertility problems: assessment and treatment (CG156) · Sheynkin Y et al., Increase in scrotal temperature in laptop computer users, Hum Reprod 2005;20(2):452-5 · Mínguez-Alarcón L et al., Type of underwear worn and markers of testicular function, Hum Reprod 2018;33(9):1749-56 · Sharma R et al., Cigarette smoking and semen quality: a new meta-analysis, Eur Urol 2016;70(4):635-45 · Sermondade N et al., BMI in relation to sperm count, Hum Reprod Update 2013;19(3):221-31 · Gundersen TD et al., Association between use of marijuana and male reproductive hormones and semen quality, Am J Epidemiol 2015;182(6):473-81 · Robbins WA et al., Walnuts improve semen quality in men consuming a Western-style diet, Biol Reprod 2012;87(4):101 · Schisterman EF et al., Effect of folic acid and zinc supplementation in men on semen quality and live birth, JAMA 2020;323(1):35-48 · Steiner AZ et al., The effect of antioxidants on male factor infertility: the MOXI trial, Fertil Steril 2020;113(3):552-60 · Garolla A et al., Seminal and molecular evidence that sauna exposure affects human spermatogenesis, Hum Reprod 2013;28(4):877-85 · Educational only, not medical advice.

Keep reading: Will TRT make you infertile? · Varicocele: the fixable cause · Does cannabis lower testosterone? · What causes low testosterone · Does TRT cause infertility? · Blood test: what to check