The headlines were dramatic. Tages-Anzeiger declared: “Sperm crisis in Switzerland – a city–countryside divide in sperm quality.” Blick wrote: “If you live in these regions, you have a sperm problem.” Apparently, the reproductive capacity of young men is compromised in certain parts of Switzerland.

These reports are based on a study that analysed sperm samples from nearly 2,700 Swiss military recruits. In addition to the samples, the young men completed questionnaires about their living conditions. An earlier analysis of the same data already showed in 2019 that maternal smoking during pregnancy is associated with reduced sperm quality in the offspring later in life.

In the new investigation, the quality of the ejaculate was analysed in greater detail. The guiding research question was: are there geographical regions in Switzerland where sperm quality is worse than elsewhere? The results appear to support this assumption. Recruits from the Aare Valley between Bern and Thun performed worse on several quality parameters than those from other regions. At the top end of the scale is the area around Aarau, where sperm quality was reportedly the best.

This spatial distribution led the researchers to the following conclusion: “We found clear geographical patterns of comparatively lower sperm quality parameters among young men that were associated with higher proportions of surrounding agricultural land.” Translated: the more agricultural the area of residence, the poorer the sperm quality. The presumed culprit therefore seems obvious – pesticides.

«We have no idea whether pesticides play a role»

Tages-Anzeiger accordingly wrote: “The data collected provide clear indications that pesticides could play a role in male fertility. However, causal proof is still lacking.”

But a sentence that begins with “clear indications” and ends in the conditional is hardly convincing. Correlation alone does not imply a cause-and-effect relationship (causality). And in fact, the data do not support such a link for several reasons. This is also pointed out in an article in the St. Galler Tagblatt: “Surprisingly, the Bernese Seeland, known as the ‘vegetable garden of Switzerland’, does not stand out as a region with low sperm quality. Vegetable cultivation involves particularly intensive pesticide use.” The study’s authors themselves emphasise this contradiction. In a report by SRF, they are quoted as saying: “We have no idea whether pesticides play a role.”

Despite these limitations, one message sticks in the public perception: pesticides are to blame.

In addition, the study design does not allow for robust causal conclusions. The number of cases examined in the individual regions is simply too small. The “top region” around Aarau includes only 31 recruits, while the area around Bern includes just 24. “Only a study with many more participants can deliver meaningful results,” rightly notes the Aargauer Zeitung. The authors themselves explicitly point this out.

In the end, one thing is clear above all: before speculating about causes, far more robust data are needed – everything else is more conjecture than science.