Could a postal code help shape male fertility? A study of 386 men in Spain found that participants in the northern region averaged 94.35 million motile sperm per sample, compared with 50.11 million in central Spain, even though their reported lifestyles were broadly similar.
The findings were presented in London in July 2026 at the annual meeting of the European Society of Human Reproduction and Embryology. They do not prove that northern environments protect sperm or that pollution harms men elsewhere.
However, since smoking, alcohol, exercise, body weight, coffee, drugs, medications, and other measured factors did not explain the pattern, the researchers say environmental exposure deserves a much closer look.
The north stood out
The northern group recorded the strongest overall semen results, including the highest average sperm concentration and the best motility. Motility is simply the ability of sperm to move, an essential step when sperm must travel through the reproductive tract to reach an egg.
About 44.79% of sperm in northern samples were moving. Reduced motility affected 23.9% of men in the north, compared with 55.4% in the south and 53.4% in central Spain. That is a wide gap, not a small statistical wrinkle.
How researchers tested it
The prospective study began with 442 men between June 2024 and December 2025, then included 386 who met the criteria. All were undergoing fertility assessment at seven assisted reproduction centers and were grouped into northern, southern, southeastern, and central regions.
Participants answered a standard questionnaire about residence, body mass index, medical history, exercise, chemical exposure, medication use, smoking, alcohol, recreational drugs, and coffee. In everyday terms, the team tried to separate where the men lived from how they lived.
Laboratories measured semen volume, sperm concentration, motility, shape, and the total number of moving sperm. That last measure combines how many sperm are present with how many can move, giving clinicians a practical view of a sample.
Researchers also accounted for abstinence time because the number of days since ejaculation can change the result.
Pollution is a clue
Lead author Rocío Núñez-Calonge, a human reproduction specialist and scientific advisor to UR International Group, said, “What was most remarkable for us was that the strongest semen quality parameters were consistently found in northern Spain.” She added that the similarity in lifestyle patterns across the regions surprised the team.
Simply put, location can bundle together exposures that individuals cannot fully control, including urban air pollution, industrial chemicals, intensive agriculture, and compounds released from plastics. Yet the study measured none of these directly, so pollution remains a plausible explanation, not a demonstrated cause.
Sperm DNA offers another clue
A separate study presented at the same London meeting gives the pollution hypothesis more biological detail. Carrie Nobles of the University of Massachusetts Amherst and colleagues enrolled 2,015 men near Salt Lake City, with sperm DNA methylation measured in 1,220 participants.
DNA methylation means chemical tags that can turn gene activity up or down without changing the DNA code itself.
The researchers associated mixtures of common air pollutants during the roughly three months when sperm develop with 39 methylation changes.
Ozone and nitrogen dioxide made the strongest contributions, and one affected gene called GNAS has previously been tied to poorer semen quality and embryo development. That does not mean a traffic jam causes infertility, but it shows one route by which polluted air might reach reproductive biology.
A healthcare professional uses an anatomical model to explain the female reproductive system during a fertility consultation with a couple.
The limits matter
The Spanish results came from men who had already sought fertility testing, not a random sample of the public. Each participant provided only one semen sample, while semen characteristics can change over time, and lifestyle answers were self-reported.
Rita Vassena, medical director of fertility at CooperSurgical, noted that broad regions cannot show whether someone lived in an industrial area or near intensive farmland. Without exact exposure data, researchers cannot know what environmental feature, if any, created the difference.
Most important, this observational study cannot prove cause and effect. It also should not be read as evidence that healthy habits do not matter, only that the measured habits did not explain this particular regional pattern. The map is a clue, not a diagnosis.
Why this matters beyond Spain
A major global meta-analysis of 223 studies reported that average sperm concentration among men recruited without regard to fertility fell 51.6% between 1973 and 2018. Scientists still debate the size and causes of the trend, but the long-running concern makes geographic clues like these harder to dismiss.
At the end of the day, the new work shifts the question from only “What habits does a man have?” to “What is he breathing, touching, and living around?” Larger population studies will need repeated semen samples, precise exposure maps, and biological markers before researchers can say why northern Spain performed better.
The official study abstract was published in Human Reproduction.
