Sperm health and paternal preconception
Sperm are made fresh, over and over, on a cycle of about three months. That single fact makes sperm composition and quality the most influential part when it comes to conception.
This covers what improves a semen analysis, and what the evidence does not support. If you have not read through the rest of the work-up, start with how to read your fertility test results.
Why does sperm get tested last?
A semen analysis is one non-invasive test that your GP can order, and it is still commonly left until after months of investigation on the female side.
Healthy Male, Australia's national men's health organisation, funded by the Australian Government Department of Health, Disability and Ageing, puts it carefully: male infertility might be a contributing factor for up to half of infertile couples, but we do not know for sure.¹
A new review in The Lancet argues the framing itself is the problem. It found a man's weight, substance use, age and his own early life experiences all shape pregnancy and child outcomes, and that for some outcomes, the paternal influence exceeds the maternal one.² It maps patterns across disciplines rather than proving cause.
After 12 months of trying, both of you should be assessed.¹
How long does it take to change sperm health?
New sperm take around three months to develop fully, so a change made now shows up in a semen analysis about three months later.³
That’s why quitting smoking is advised at least three months before trying, rather than at the positive test.³ It is also why one sample is a snapshot rather than a verdict. Semen quality varies day to day and can be affected by illness or infection, which is why at least two analyses, six weeks apart, are needed to assess fertility properly.¹
Eggs cannot be remade, and the strongest determinant of egg quality is age. Sperm are produced continuously, so most of what affects them can be changed and then measured again. That is the argument for acting on the sperm side early rather than late.
What affects sperm health
Four things have consistent evidence behind them: weight, smoking, heavy alcohol use and age. The size of each effect varies.
Does being overweight affect sperm count?
Being overweight or obese is associated with a higher chance of a low sperm count, or no sperm in the sample at all, and that association rises with body weight.
In a meta-analysis of 21 studies covering 13,077 men, the odds of a low or absent sperm count were 11% higher in overweight men, 28% higher in obese men and about twice as high in men with a BMI over 40, compared with men in the healthy weight range.⁴ Sperm concentration on its own did not differ significantly across weight categories, so the categorical risk moved while the average concentration did not.⁴
This is pooled observational data, so it describes an association rather than proving cause. The authors name their main limitation directly: the studies mixed men from the general population with men attending fertility clinics.⁴
How much does smoking affect sperm quality?
Smoking is associated with a measurably lower sperm count, poorer movement and fewer normally shaped sperm.
A meta-analysis of 5,865 men found smokers had roughly 9.7 million fewer sperm per millilitre, about 3.5 percentage points lower total motility and about 1.4 percentage points fewer normally shaped sperm than non-smokers.⁵ These are group averages from observational studies, so they describe a population shift.
The dose matters. The more cigarettes, the worse the sperm quality, although even light smokers, meaning fewer than 10 cigarettes a day, have reduced sperm quality.³ Quitting at least three months before you start trying is the standing advice.³
Does drinking alcohol affect sperm?
Occasional drinking is unlikely to affect fertility but heavy drinking reduces sperm quality. Where the line falls between the two is not known.
Healthy Male states that the occasional drink is unlikely to matter, while heavy drinking can lower sperm quality and testosterone production. It then says something most health content will not, which is that we do not know exactly how much alcohol affects fertility, so moderation is the safest position and reducing or stopping three months ahead is recommended for optimal fertility.³
That is the accurate reading of this evidence. Almost all of it is observational, drinking is self-reported, and men who drink heavily differ from men who do not in ways that are hard to account for. If you want a specific number of drinks, there is not a defensible number to give you.
Does a man's age affect miscarriage risk?
Advanced paternal age is associated with a modestly higher risk of miscarriage but the effect is smaller than the one that comes with maternal age.
A systematic review pooled nine studies, all of which had adjusted for at least maternal age. Compared with fathers aged 25 to 29, the pooled risk of miscarriage was 1.04 for ages 30 to 34, 1.15 for 35 to 39, 1.23 for 40 to 44 and 1.43 for 45 and over.⁶ Only the last two were statistically significant, so the signal appears from about 40 onwards.
The included studies are observational, and the authors say directly that residual confounding by maternal age cannot be excluded, because older men tend to have older partners.⁶
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Do supplements work?
CoQ10 improves the numbers on a semen analysis.
A 2025 meta-analysis pooled eight randomised trials covering 877 men.⁸ Against placebo or no treatment, CoQ10 raised total sperm count by about 13 million, total motility by about 7 percentage points, progressive motility by about 6 points and normally shaped sperm by about 2 points.⁸ Semen volume and sperm concentration did not move.⁸
Importantly, not one of those trials reported pregnancy or live birth. An earlier meta-analysis that went looking specifically for those outcomes found no trial reporting live births and no increase in pregnancy rates.⁹
So CoQ10 does improve the count.
Omega-3 is consistently associated with better semen parameters.
A systematic review found 16 studies on omega-3 and semen quality, and 14 reported an improvement in, or an association with, at least one semen marker.¹⁰ The reviewers did not pool them, because the studies differed too much in participants, dose and duration.¹⁰
The largest dataset is cross-sectional. Among 1,679 young men, the 98 who used fish oil had higher semen volume, larger testes and higher total sperm count, at a standardised 184 million for men using it 60 days or more against 147 million for men using nothing.¹¹
Those men also smoked less and were fitter than non-users, and the study never measured what was in the capsules.¹¹
The evidence that antioxidant supplements improve live birth for subfertile men is very low certainty and it weakened as more trials were added rather than strengthening.
The Cochrane review, updated in 2022, included 90 randomised trials and 10,303 subfertile men at fertility clinics.⁷ It found antioxidants may improve live birth rates, but rated that very low certainty because of poor reporting of randomisation, few trials measuring live birth at all, high dropout and small samples.⁷
None of this is to say that a general preconception multivitamin a bad idea. We cover the same question on the female side in CoQ10 and egg quality.
What this means for you
Book your partner’s semen analysis in the same round as your own bloods rather than months later.
Some tips for the test: he should abstain from ejaculating for at least two days beforehand and a sample produced at home needs to reach the lab within about 30 minutes, kept warm.¹ Ordinary condoms and lubricants cannot be used, because most lubricants are toxic to sperm.¹
Treat one result as provisional. Two analyses at least six weeks apart are what properly assess fertility.¹ Sperm DNA fragmentation testing is not recommended in most professional guidelines, so it is not part of a routine work-up.¹ Home kits are not as accurate as the laboratory test.¹
Then use the three month window to plan your preparation: a basic multivitamin, add in CoQ10 and Omega-3 fish oil tablets to improve your sperm count.
The rest of the list is in our preconception checklist and most of it applies to both of you.
References
- Healthy Male. What happens during a semen analysis for male fertility. Melbourne: Healthy Male; 2024.
- Huang JY, Schoenaker DAJM, Godfrey KM, et al. More equitable preconception health: paternal life course opportunities for better pregnancy, child, and family outcomes. Lancet. 2026.
- Healthy Male. Sperm health. Melbourne: Healthy Male; 2024.
- Sermondade N, Faure C, Fezeu L, et al. BMI in relation to sperm count: an updated systematic review and collaborative meta-analysis. Hum Reprod Update. 2013 May-Jun;19(3):221-31.
- Sharma R, Harlev A, Agarwal A, et al. Cigarette smoking and semen quality: a new meta-analysis examining the effect of the 2010 World Health Organization laboratory methods for the examination of human semen. Eur Urol. 2016 Oct;70(4):635-45.
- du Fossé NA, van der Hoorn MLP, van Lith JMM, et al. Advanced paternal age is associated with an increased risk of spontaneous miscarriage: a systematic review and meta-analysis. Hum Reprod Update. 2020 Sep-Oct;26(5):650-69.
- de Ligny W, Smits RM, Mackenzie-Proctor R, et al. Antioxidants for male subfertility. Cochrane Database Syst Rev. 2022 May 4;5(5):CD007411.
- Akhigbe TM, Fidelis FB, Adekunle AO, et al. Does coenzyme Q10 improve semen quality and circulating testosterone level? A systematic review and meta-analysis of randomized controlled trials. Front Pharmacol. 2025 Jan 3;15:1497930.
- Lafuente R, González-Comadrán M, Solà I, et al. Coenzyme Q10 and male infertility: a meta-analysis. J Assist Reprod Genet. 2013 Sep;30(9):1147-56.
- Falsig AM, Gleerup CS, Knudsen UB. The influence of omega-3 fatty acids on semen quality markers: a systematic PRISMA review. Andrology. 2019 Nov;7(6):794-803.
- Jensen TK, Priskorn L, Holmboe SA, et al. Associations of fish oil supplement use with testicular function in young men. JAMA Netw Open. 2020 Jan 3;3(1):e1919462.
Written by Bella · BBiomedSc, MEpi · Clinical epidemiologist
I read pregnancy research so you do not have to. More about me
Published: 8th September 2026 · Last reviewed: 8th September 2026
How I review research: Editorial policy
Educational only, not medical advice. Full disclaimer
This article is for educational purposes only and does not constitute medical advice. Research findings describe patterns across populations and may not apply to you. Always discuss your own situation with your GP, midwife or obstetrician.
