Sperm concentrations across the global male population fell by 51.6 percent between 1973 and 2018. The average count dropped from 101.2 million sperm per milliliter to 49.0 million per milliliter, according to a meta-analysis of data from 53 countries (Levine et al., Human Reproduction Update, 2023).
Walk through any pharmacy and you will see the answer to that decline. Capsules, powders, gummies, all labeled as fertility supplements for men. What the labels skip is how small the underlying trials really were.
Male fertility science is younger and thinner than most men assume. Supplement companies built their category inside that gap. Some of the strongest evidence about what affects sperm does not come in a pill at all.
Male fertility research started decades behind
Doctors treated infertility as a women's health issue for most of the 20th century. The male side of a workup usually started and stopped with a semen analysis, and that test took years to standardize. The World Health Organization published its first laboratory manual for human semen analysis in 1980. Before that, labs used their own methods and their own definitions of normal, which made comparisons across studies close to useless.
The first real alarm came in 1992. A Danish group led by Elisabeth Carlsen analyzed 61 semen studies covering about 15,000 men. They reported that average sperm density had fallen from 113 million per milliliter in 1940 to 66 million per milliliter in 1990 (Carlsen et al., British Medical Journal, 1992). Critics pointed out that different labs counted sperm differently, the studies came from uneven geographies, and men who visit fertility clinics are not a random sample of the general population.
The decline held up under better methods. A 2017 meta-analysis confirmed the trend, and the Levine update in 2023 extended it across 53 countries. That is where the 51.6 percent drop comes from.
Companies moved into the decades-long lag between alarm and understanding. Researchers could see counts falling, but the causes stayed murky. Supplements stepped in before the science could explain much of anything.
The evidence behind the supplement labels
Most male fertility supplements are built on the biology of oxidative stress. Sperm cells are unusually easy to damage because of two quirks.
- Their membranes carry high amounts of polyunsaturated fatty acids, which makes them flexible but also prone to attack by reactive oxygen species.
- Mature sperm keep almost no cytoplasm, so they have little of the repair machinery that other cells use to fix oxidative damage.
That logic points toward antioxidants. Give the body more of them, lower the oxidative load, and sperm parameters might improve in theory. The nutrients on most labels all play roles in that system. Zinc, selenium, coenzyme Q10, vitamin C, vitamin E, folate, and omega-3 fatty acids.
You can get every one of those from food.
- Oysters and pumpkin seeds carry zinc.
- Brazil nuts are dense in selenium.
- Fatty fish and organ meats contain coenzyme Q10.
- Leafy greens and legumes supply folate.
That food point matters for a reason most supplement trials ignore. Many studies recruit men without ever documenting their baseline nutrient status. A man who walks into a trial with normal zinc levels is not the same as a man with a deficiency, and lumping them together blurs whatever signal exists.
The evidence for turning those nutrients into pills is thinner than the label copy suggests. A Cochrane review pooled randomized trials of antioxidant supplements in subfertile men. It found low-certainty evidence that the supplements may improve live birth rates compared to placebo (Smits et al., Cochrane Database of Systematic Reviews, 2019). Low certainty means the estimate could change once better studies appear. Most trials in the review were small, lasted a few months, and measured sperm count, motility, or morphology instead of whether a partner got pregnant at all.
Sperm parameters are a proxy. A pill can move a lab value without changing the outcome that matters. That gap between proxy and pregnancy is where a lot of supplement marketing lives.
The factors that are not on the shelf
The most consistent, replicable findings about male fertility point to heat and everyday chemicals, not to anything you swallow.
Heat has the strongest evidence
Sperm production needs the testicles to run a few degrees below core body temperature. When that gap closes, sperm output drops. A study in Human Reproduction followed men who used saunas regularly and found that sperm count and motility fell during regular heat exposure, then recovered after the men stopped (Garolla et al., Human Reproduction, 2013). A separate paper found the same pattern with wet heat exposure. Stopping the exposure allowed semen quality to recover (Shefi et al., Fertility and Sterility, 2007).
Tight underwear and long periods of sitting raise scrotal temperature when compared to looser underwear and movement (Jung et al., Human Reproduction, 2005). A separate measurement of scrotal temperature found that tight clothing raises it compared to looser options (Mieusset et al., Journal of Andrology, 2007). In a fertility-center cohort, men who reported wearing looser, boxer-style underwear had higher sperm concentration and total count than men who wore tighter styles (Minguez-Alarcon et al., Human Reproduction, 2018). A laptop resting on the thighs raises scrotal temperature in healthy young men (Sheynkin et al., Human Reproduction, 2005).
Swapping tight briefs for looser shorts is less exciting than a supplement, but the evidence behind it is more direct.
Chemicals matter more than most men think
A 2024 meta-analysis in Toxics found that BPA exposure was associated with poorer sperm parameters (Lu et al., 2024). Phthalates and other plastics chemistry have been studied for their effects on male reproductive health for years (Rodprasert et al., Frontiers in Endocrinology, 2021). Microplastics now show up in human testicular tissue and semen when labs use sensitive detection methods (Hu et al., Toxicological Sciences, 2024. Zhao et al., Science of the Total Environment, 2023).
There is a caveat, and it matters. Those microplastics studies establish presence, not proven cause. No study has traced particles found in human testes to clothing or any single source. The link between microplastics and reduced fertility in humans remains association, not proof.
The scrotum is also one of the most permeable patches of skin on the body. Early human absorption studies measured regional skin differences and found scrotal penetration far above the forearm baseline (Maibach et al., Archives of Environmental Health, 1971). Fabric chemistry can migrate into sweat, and skin takes up more of what touches it when it is warm, damp, and covered. That combination describes the all-day wear situation for most men. Synthetic clothing worn directly against the skin is another contact point, though no study has measured what that specific exposure does to a man's sperm.
The clearest moves involve removal. You stop the heat, you loosen the fit, you reduce the chemical contact. None of that comes in a capsule.
A practical approach to the supplement aisle
Start with the boring parts. Get bloodwork done by a doctor who can check your zinc, vitamin D, folate, and selenium status. Supplements make the most sense when a specific deficiency shows up on a lab report. Before that, the food sources are cheaper and come with fewer unknowns. Oysters, pumpkin seeds, Brazil nuts, leafy greens, fatty fish, and eggs cover a lot of the same ground.
After you know your numbers, heat is the next place to look. If you use a sauna regularly and are trying to conceive, ask your doctor whether pausing for a while makes sense for you. Some men choose to stop for a few months. Looser underwear costs nothing. A laptop off the lap is free. The studies suggest heat effects reverse once the exposure stops.
Then look at the chemicals around you. Receipt paper is one source of BPA exposure. Wash your hands after handling receipts and decline printed receipts when you can. Plastic containers and plastic wrap around hot food leach more. Synthetic clothing worn directly against the skin all day is one more contact point.
None of this is dramatic. It is just the side of the evidence that does not photograph well for an ad campaign.
The supplement question only becomes reasonable after those boxes are checked. Even then, a doctor should be the one to decide what you take and in what amount. I am not listing dosages here on purpose. The evidence does not support a universal male fertility stack, and the trial data are too inconsistent for one-size-fits-all advice.
Research on this topic is moving. The microplastics findings from 2023 and 2024 are new, and the next few years will show whether they mature from presence into cause. What you can act on today is older and less glamorous: blood work, food, heat, and a hard look at the plastics that touch your body.
This content is for educational purposes only and is not medical advice. Oakman products are designed for physical comfort and cooling. They make no claims about fertility, sperm quality, or hormone levels. Consult a healthcare professional for personalized advice.
Frequently asked questions
do fertility supplements improve sperm count?
Some trials show improvements in sperm count, motility, or morphology, but the evidence is low certainty. A Cochrane review found low-certainty evidence that antioxidant supplements may improve live birth rates compared to placebo. Many studies were small and measured lab values rather than pregnancy outcomes. A doctor can help you decide if a specific supplement makes sense after checking your nutrient levels.
what nutrients matter most for male fertility?
Zinc, selenium, coenzyme Q10, vitamin C, vitamin E, folate, and omega-3 fatty acids show up most often in fertility research. You can get all of them from food. Oysters, pumpkin seeds, Brazil nuts, fatty fish, organ meats, leafy greens, and legumes cover most of the ground. Lab work can show whether you have a specific deficiency worth addressing.
does sauna use lower sperm count?
Regular sauna use can temporarily lower sperm count and motility. The effect reverses once heat exposure stops because sperm production needs the testicles a few degrees cooler than core body temperature. If you are trying to conceive, ask your doctor whether pausing sauna use makes sense for you.
can microplastics reduce male fertility?
Microplastics have been found in human testicular tissue and semen. Those findings establish presence, not proven cause. The link between microplastics and lower fertility in humans is still association, not proof.