A recent study revealed that sperm quality varies significantly across Spain, with men in the northern regions producing healthier sperm samples compared to those in central and southern areas. The findings were published in the journal Human Reproduction.
Despite similar lifestyles, men in the north had nearly twice as many active, motile sperm on average as those in central Spain. This difference persisted even after researchers accounted for diet, weight, smoking, alcohol consumption, and physical activity. These habits were strikingly consistent across the regions.
Consequently, environmental factors remain the primary suspects, including possible air pollution, industrial chemicals, and other contaminants.
The study involved 386 men who visited fertility clinics for evaluations at seven reproductive medicine centers in Spain between mid-2024 and late 2025. Their questionnaire was comprehensive, extending far beyond just the analysis of the sperm sample.
Each man reported his residence, weight, medical history, exercise habits, smoking, alcohol and coffee intake, and exposure to workplace chemicals.
The analysis was led by Professor Rocío Núñez-Calonge, a biologist specializing in human reproductive function and a scientific advisor to the International UR Group (UR). She and her team presented the results at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE).
To compare regions, the team divided the country into four large zones: north, south, southeast, and center. They juxtaposed standard sperm quality metrics. The most accurate fertility indicator is the total number of motile sperm in a full sample, which combines volume, concentration, and motility.
The regional results were not uniform. Men from northern regions clearly had an advantage, averaging about 94 million motile sperm per sample. In contrast, central Spain averaged around 50 million. Northern Spain also led in other key indicators.
Sperm concentration there was higher, at about 81 million per milliliter, and a larger proportion, roughly 45% on average, were in motion. The sharpest contrast was in sperm motility—the percentage of sperm capable of swimming normally. In the north, poor motility was observed in about one in four men.
In the south, this rate exceeded half, and in central Spain, it was nearly as high. Sperm morphology followed the same trend. Irregularly shaped sperm were also more common in the south and center, reinforcing the same pattern across all measures.
The most obvious explanation was lifestyle. Northern Spain might simply have leaner men, fewer smokers, or people with different exercise habits. The data did not support this. Across all four regions, the self-reported habits were remarkably similar.
When researchers accounted for all the lifestyle and background factors they measured, nearly all ceased to be viable explanations. Only two factors remained significant. Geographic location and abstinence time—the period a man had not ejaculated before providing a sample—were the only factors independently linked to the results.
Geographic differences in sperm production are real and can manifest over surprisingly short distances. This conclusion came from a comprehensive analysis of data spanning four decades, though with the caveat that claims of a global decline rest on shakier grounds.
What makes this result striking is that geographic location remained significant even after lifestyle factors were excluded.
“The best sperm quality indicators were consistently observed in northern Spain,” stated Núñez-Calonge.
If personal habits don’t account for the gap, the search shifts to the environment. Núñez-Calonge and her colleagues suggest that regional differences stem from environmental exposure. Pollution and its associated substances can vary from one part of the country to another.
This is not new. An earlier 2024 study involving over 2,000 men from 12 Spanish regions found that Asturias, in the far north, ranked first, while Granada, in the south, ranked near the bottom.
None of this proves that environmental pollution weakens sperm, and the men in the study initially sought help for infertility, not being selected from the general public.
Nevertheless, the same north-to-south pattern observed in separate studies prompts researchers to continue viewing the environment as a genuine factor influencing male fertility.
The link between industry and low sperm counts goes even deeper. A 2008 study of young Spanish volunteers showed that low sperm counts were most common in Valencia, Barcelona, and the Basque Country.
Over the previous half-century, these were the country’s most industrialized regions, while less industrialized Galicia and Andalusia had the lowest rates. The stakes go beyond the clinic. If a man’s place of residence affects fertility, then protecting the environment becomes a measure for safeguarding reproductive health.
Professor Karen Sermon places responsibility on regulatory bodies, not individuals.
“There is a clear responsibility on national and European regulatory authorities,” said Sermon. The evidence is limited but consistent.
In Spain, sperm quality depends on geographic location, even when lifestyle is not a determining factor, and the most compelling explanation now lies not in personal choices but in the environment.
The next step is to measure pollutant levels in men’s sperm samples from each region and identify which factors are most closely linked to declining sperm quality.
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