Geographical differences in semen quality in Spain are not linked to men’s lifestyle habits

This study aims at assessing whether there are associations between the quality of semen samples in men attending fertility clinics and some lifestyle or individual factors in Spain. Alterations in semen characteristics have previously been reported in Spain, however the reason for these differences was not clarified. More broadly, the state of male fertility is becoming a focus of research given the reported global decrease in sperm concentration over recent decades, the overall lower fecundity, and increase in couples needing assisted reproduction to conceive. It is a field where lifestyle and exposure factors, as well as genetic determinants, intersect in creating the observed outcome. To make matters more complicated, the characteristics of semen in an ejaculate fluctuate in response to both known factors (such as abstinence) and unknown ones, so it is often necessary to analyse more than one sample from the same person to have a strong assessment.

Taking into consideration the intrinsic limitations of these types of studies, the study by Rocio Nuñez-Calonge is nonetheless interesting, particularly because it seems to conclude that there are regional differences in sperm quality that supersede the effect of self-reported lifestyle factors. If confirmed, this would indicate that the most likely exposure factors are independent from lifestyle choices such as smoking or exercising. The number of men tested in this study is quite large and this gives strength to the outcomes, however the broad division of the Spanish territory makes it almost impossible to understand what the reason of the observed differences could be. For instance, it has been shown that men living in either highly industrialized areas or in areas of intensive agriculture tend to have worse semen parameters, likely due to exposure to environmental contaminants. In the present study, we do not know the environment where the men lived, just the broad geographical region. Another point is the fact that the participants were attending a fertility clinic, and although they were receiving a semen assessment – not a fertility treatment - most men in the general population do not have these type of assessment, so that there may be an effect of self-selection of a population already at risk of altered semen parameters.

All in all, it is an interesting study in a large number of cases that opens the door to further understanding of the factors affecting male semen quality beyond lifestyle choices.

Semen quality is highly variable among individuals, with many factors potentially influencing it. One of the problems in addressing the impact of factors on spermiogram parameters are confounding factors. The study by Núñez-Calonge et al. aims to determine whether there is a geographic impact related to environmental exposure on sperm quality, or whether lifestyle factors act as confounders in that relationship.

The study, conducted in a cohort of 386 men in Spain, demonstrates that semen volume, concentration, motility, and morphology consistently differ across four regions in the country, with the highest total motile sperm count observed in the northern region and the lowest in the central region. Remarkably, the study controls confounding variables and reports that geographical location is independently associated with sperm quality and with the prevalence of asthenozoospermia and teratozoospermia diagnoses.

In my opinion, this research is pertinent because it demonstrates, under the control of potential confounding factors, that environmental factors have a significant influence on semen quality. This is relevant for future research interrogating the multiple factors that shape semen quality in humans.

This prospective study reaffirms that geographical differences in semen quality persist even after adjusting for lifestyle factors or physical activity. This suggests that these habits, on their own, would not account for the variations observed between regions, and that other determinants must be considered, in particular environmental exposures.

In this context, endocrine disruptors could be a particularly relevant hypothesis. These are chemicals found in plastics, pesticides, cosmetics and many everyday products, capable of interfering with the hormonal system even at low doses. The available scientific evidence indicates that exposure to these compounds, particularly during critical stages of development, can have long-lasting effects on male reproductive function.

Although this study does not establish causal relationships nor does it directly assess these exposures, its findings reinforce the need to investigate the role of environmental pollutants in reproductive health in greater depth, using objective biomarkers and more precise study designs.

This is a prospective, multicenter study with an appropriate methodology and statistical analysis that attempts to account for numerous potential confounding factors, such as smoking, alcohol consumption, body mass index, and physical activity. Its main contribution is to show that the geographical differences observed in semen quality among different regions of Spain persist even after adjusting for these lifestyle-related factors.

However, these results should be interpreted with caution. The study includes men who sought assisted reproductive technology services, so it is not representative of the general population. Furthermore, information on lifestyle habits comes from self-reported questionnaires, semen analysis is based on a single sample per participant, and, most importantly, environmental exposures—which could explain some of the observed differences—were not directly measured. As this is an observational study, it also does not allow for the establishment of causal relationships.

These results are consistent with previous studies that had described geographic variations in semen parameters, but they offer a significant innovation by systematically incorporating lifestyle variables into the analysis. The fact that these variables explain only a small portion of the differences suggests that other factors—possibly environmental or context-related—warrant further investigation in future studies.

From a clinical standpoint, this study does not alter current recommendations for men. Maintaining a healthy lifestyle remains important for reproductive and overall health, even though this study indicates that the observed regional differences cannot be attributed solely to those habits. It would be a mistake to interpret these results as proof that lifestyle does not influence male fertility. What it does show is that, in this specific cohort and after adjusting for the analyzed factors, geographical differences persist, the explanation for which requires further research.

I believe the main point that should be conveyed to journalists is to avoid headlines such as “Lifestyle does not affect semen quality” or “Living in a certain region determines male fertility.” The study does not prove either of these two claims; it merely indicates that the geographical differences detected in this cohort are not explained by the lifestyle variables included in the study, which suggests the possible involvement of other, as yet unidentified factors.

The study is interesting, but I think it is still too early to conclude that it demonstrates regional differences in sperm quality throughout Spain without taking into account many other lifestyle-related factors that were not considered in this study. I think it is an interesting starting point, and I congratulate the authors on this study, but given the data, I believe the statistical analysis should account for other potential confounding factors that may vary by region.