Wilcox, Allen J.
Are sperm counts declining over time? This question has been fiendishly difficult to address. Measurements of semen parameters are fraught with problems at every level: wide variations within a given man, incomplete and selective participation among groups of men, difficult-to-control confounding factors (such as abstinence time), and vagaries of laboratory methods. Without consistent collection and assay over time, we are left with confusion and conflict. Some researchers remain highly skeptical of the evidence for changes over time,1 whereas others argue that environmental pollutants (in particular, chemicals that act as endocrine disruptors) are causing serious damage to the male reproductive tract.2,3
With this as background, the commentary by Jens Peter Bonde and his colleagues4 in this issue of Epidemiology is instructive. The authors present a graph posted online by the Danish National Board of Health last March.5 The graph provides what this field has lacked for so long: sperm data from samples collected consistently and regularly over time, from an unselected population of young men (in this case, Danish military draftees), and analyzed with standardized laboratory methods. On the face of it, the results are striking; there is no evidence of a decline in sperm counts in Denmark over the last 15 years.
One might ask why these data are being presented to the scientific community in a commentary rather than as part of a research paper. It would have been much better for science (not to mention the public's understanding of this important issue) if the data had been carefully analyzed and presented by the scientists who collected them.
Instead, the researchers responsible for these data have criticized the Danish Board of Health for posting the data.6 In the researchers' opinion, these data should not have been released before the accumulation of at least 20 years of results.6,7 (The basis for this time table is not clear—the same research group recently showed a decline in sperm counts using Finnish data that span 8 years.8) The Web posting by the Danish Board may indicate some impatience on the agency's part that the Danish data remain unpublished.
Who owns data generated with public funds? The editors of Epidemiology have discussed problems that can arise when researchers restrict access to scientific data.9 The agency's posting of a few raw data is a limited remedy. Data do not speak for themselves—they need context, and they need skeptical evaluation. Bonde and his colleagues are able to set the data into scientific context and (within the limits of the scant data) provide preliminary interpretation. As the commentators discuss, these data do not rule out the possibility that Danish sperm counts could have declined before 1996. Some studies suggest that sperm concentrations may be lower in Denmark than in other populations.10,11 Still, these serially collected data from Denmark appear to be superior to nearly all of what has come before. And, as the commentators note, it remains an odd coincidence that a decline in sperm counts would have ended just as a proper surveillance study was put into place.
The presentation of a few raw data on a Web site—or in a commentary—is hardly the preferred way to advance science. But neither is it acceptable for valuable data to be held in storage. The publication of these data in Epidemiology does not foreclose the opportunity for researchers to prepare a full and careful analysis of their data. Indeed, the field deserves no less.
1.Fisch H. Declining worldwide sperm counts: disproving a myth. Urol Clin North Am. 2008;35:137–46, vii.
2.Sharpe RM, Skakkebaek NE. Are oestrogens involved in falling sperm counts and disorders of the male reproductive tract? Lancet. 1993;341:1392–1395.
3.Skakkebaek NE, Rajpert-De Meyts E, Main KM. Testicular dysgenesis syndrome: an increasingly common developmental disorder with environmental aspects? Hum Reprod. 2001;16:972–978.
4.Bonde JP, Ramlau-Hansen CH, Olsen J. Trends in sperm counts: the saga continues. Epidemiology. 2011;22:617–619.
8.Jorgensen N, Vierula M, Jacobsen R, et al. Recent adverse trends in semen quality and testis cancer incidence among Finnish men. Int J Androl. In press.
9.Hernán MA, Wilcox AJ. Epidemiology, data sharing, and the challenge of scientific replication. Epidemiology. 2009;20:167–168.
10.Jorgensen N, Andersen AG, Eustache F, et al. Regional differences in semen quality in Europe. Hum Reprod. 2001;16:1012–1019.
11.Jorgensen N, Asklund C, Carlsen E, Skakkebaek NE. Coordinated European investigations of semen quality: results from studies of Scandinavian young men is a matter of concern. Int J Androl. 2006;29:54–61.
© 2011 Lippincott Williams & Wilkins, Inc.