Of course, the suggestion that sperm counts may be declining is not a new one, and scientists have debated the hypothesis many times since the 1950's. But the publication of a paper by Elizabeth Carlson in the British Medical Journal in 1992 initiated a popular interest in the topic by journalists and the public alike. Many authors have since reported either how they have observed in their clinics a decline in sperm concentration in recent years (giving support to the hypothesis), or reported no apparent change (therefore refuting it). As such, the data is tantalisingly complex for all but the specialist reader and it is no wonder that journalists and some scientists are often confused by it.
What seems to be clear is that the factors that control and influence male fertility are unsurprisingly complex. Too many studies rely on the analysis of retrospective (archival) data, an approach that is laudable but fraught with potential biases. For example, the techniques for analysing semen in the laboratory have changed markedly over the past 20 years and an increasing emphasis on quality control could account for the some of the differences observed in some studies. In addition, men are now more willing to come forward for semen analysis than they were even a few years ago. This is because there is a greater social acceptability of infertility and also because there are now more treatment options available to overcome male fertility that were simply not available even 10 years ago (e.g. ICSI). As such, it may be a long time before we fully understand whether sperm counts are actually on the decline and, if so, what the cause of this might be.
Studies such as the one from Aberdeen are important pieces of a complex jigsaw, but what is required are more in-depth prospective studies which investigate the reproductive health of men in advance of attempts to conceive and possibly even from early in their adult or adolescent life. Such approaches are not cheap and will require significant funding. But surely now is the time to start such work so that if male fertility is under assault from factors unknown we have time to take preventative action?
Dr Allan Pacey is Senior Lecturer in Andrology at the University of Sheffield