Sperm: As Strong As Ever?

Source.

Sperm counts declining due to environment and chemical hazards is, seemingly, commonplace knowledge. But a startling study just published in the journal Epidemiology debunks the concept.

Highlighted in The Science Times of The New York Times {June 7 edition}:

But now 15 years of data from 18-year-old Danish men taking their military physicals show no decline in sperm counts, after all. The idea that sperm counts were plummeting began with an alarming paper published in 1992 by a group of Danish researchers. Sperm counts, they reported, declined by 50 percent worldwide from 1938 to 1991, and the trend would continue, they said.

The researchers present a single graph (which I cannot reproduce here due to copyright) that shows strikingly constant sperm count from 1996 to 2010 at about 40 million per cc, from Danish military draftees. Scientists know that a single graph cannot tell the whole story.

How was the study done?

Healthy 18-year-old men who attend a compulsory examination of fitness for military service in 2 Danish cities are encouraged to provide semen
and blood samples. Each year, from 16% to 30% have agreed, and a total of 5000 men
have provided semen samples.

From the journal's commentary:

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, whereas others argue that environmental pollutants (in particular, chemicals that act as endocrine disruptors) are causing serious damage to the male reproductive tract.

With this as background, the commentary by Jens Peter Bonde and his colleagues in
this issue of EPIDEMIOLOGY is instructive. The authors present a graph posted online by the Danish National Board of Health last March. 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.

They conclude:

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.

I agree. This is just the beginning of a thorough analysis of addressing the question regarding possible effects of the environment on sperm count, fertility and age. What about other regions around the world, communities nearby environmental disasters such as oil spills or chemical spills? What about sperm motility? Genetic modification? Effect of sample size relative to the population as a whole?

Like all good scientific observations, this study opens up many more questions than it sought to answer.