The latest predictive studies indicate that reaching 100 years old is starting to become challenging because our lifestyle habits are hindering the progress made by medical and social advances. Women live longer, and men live shorter. One way to measure men's life expectancy is found in semen.
This is what a group of Danish researchers have discovered. Their hypothesis could well be titled "tell me how many soldiers you have, and I will tell you how long you will live." Although in practice, it is more complex and still has some limitations, as the authors of the study published in Human Reproduction point out.
To test their theory, they followed a group of nearly 80,000 men for almost half a century. This led them to discover that those with a total number of mobile sperm cells (that can move or "swim") of more than 120 million could live two to three years longer than men with a total count between 0 and 5 million.
The publication is accompanied by an attached editorial comment signed by John Aitken from the School of Environmental and Life Sciences at the University of Newcastle (Australia), who describes the publication as "historic" as it is the largest study examining the relationship between semen quality and mortality.
Once again, a study focuses on semen quality and seeks a meaning beyond its impact on fertility. According to the standards set by the World Health Organization (WHO), between 30 and 50% of men of reproductive age have low-quality semen. In 2009, also a group of Danish researchers concluded that the decrease in mortality among men with good semen quality was due to a decrease in a wide range of diseases. Therefore, "the reduction in deaths could not be solely attributed to lifestyle and/or social factors."
A study published in Human Reproduction Update explains that men's sperm concentration has halved in the last five decades, mainly from 2000 to the present day, and this phenomenon is repeated similarly on all five continents, as revealed by an international study involving Spanish participation through the University of Murcia (UMU).
In fact, this premature decline in the quality of human gametes has already been analyzed in the work Espermageddon (Roca Editorial). Here, the Norwegian journalist and popularizer Niels Christian Geelmuyden delves into reasons, possible solutions, and implications. "My hope is that humanity will figure out what the problem is and take the necessary measures before we have to ensure the survival of our species by procreating from skin cells, whether our own or others'," Geelmuyden concluded the essay on the future of male fertility.
Testing the hypothesis: fewer 'soldiers,' less time alive
The research was led by Lærke Priskorn, lead researcher, and Niels Jørgensen, head of Andrology at the Department of Growth and Reproduction at Copenhagen University Hospital-Rigshospitalet (Denmark). Their team analyzed data from 78,284 men who had their semen quality evaluated between 1965 and 2015 at the public semen analysis laboratory in Copenhagen due to infertility in the couple.
This means that the quality ranged from very good to none, including those with no sperm cells. The evaluation included volume, concentration, and the proportion of mobile gametes. Priskorn points out, in a statement, that previous research had suggested that male infertility and low semen quality could be associated with mortality.
"We conducted this study to test the hypothesis and, at the same time, obtain an absolute estimate of how much a man's seminal quality predicts his longevity and to understand if diseases diagnosed before the semen quality evaluation would explain part of the reported association," the andrologist argues.
During the follow-up, the researchers used data from Danish national records to see how many died from any cause. During this time, there were 8,600 deaths, representing 11% of this group of men. Of this group, 59,657 provided semen samples between 1987 and 2015, and for this collective, more information was available, including educational level as an indicator of socioeconomic status, and registered diagnoses of medical conditions in the 10 years prior to providing a sample. The researchers adjusted their analyses to take into account the additional information available for men who provided samples from 1987 onwards, as this could affect the results.
"We calculated the life expectancy of men according to the quality of their semen and found that men with the best quality could expect to live two to three years longer, on average, than those with lower properties," Priskorn explains.
In absolute terms, males with a total mobile count of over 120 million lived 2.7 years longer than those with between 0 and 5 million. "The lower the quality, the lower the life expectancy. This association was not explained by any disease in the 10 years prior to the semen quality evaluation or the educational level of the men," she emphasized.
While the lead author highlights the strength of the study, the dataset of nearly 80,000 men, she also acknowledges the limitations. Here, she points out the lack of information on health behaviors, the assessment of men's health before semen sampling was limited to diagnoses obtained from the National Patient Register, and only for men who provided samples from 1987 onwards. Additionally, it was not possible to distinguish between men who had no mobile sperm due to an obstruction in their genital tracts and those who had no mobile sperm for other reasons.
Sperm: A clue for a new male health indicator
Scientists suggest that poor-low quality would be an indicator of other underlying factors that affect both fertility and overall health. This also presents itself as an opportunity to detect health problems at the time when gamete quality is studied.
According to the researcher, it is necessary to improve the established association. "This study suggests identifying subgroups that appear healthy when evaluated, but there is a higher risk of developing certain diseases later on," Jørgensen points out.