The French Fuss
Authorized by the Commission Nationale de l’Informatique et des Libertes , a group of French researchers reported in Human Reproduction a decrease by about a third of French sperm count over the period 1989-2005. According to these records the average count decreased from 73.6 million for milliliter to 49.9 million over 17 years – or about 2% per year.
Media attention was internationally immediate – what is happening to French men? And as lower sperm counts are associated with worsened fertility and higher rates of testicular cancer, researchers everywhere were concerned.
But are these data what they appear? Or have the media once again help obscure a complicated epidemiologic issue?
The researchers looked at sperm counts from men going to infertility clinics – 126 clinics. Out of the 154,712 men they selected those 26,609 whose partners had blocked or absent fallopian tubes.
In other words, the infertility could not be directly blamed on the males.
People going to infertility clinics are very different from the general population for reasons including:
– They’re wealthier
– They have had long term problems conceiving and perhaps other sexual dysfunction
– They’re concerned enough to spend thousands, then tens of thousands of euros about their capacity to sire children.
– They are fully self selected and not randomized.
That’s enough to know these 26 thousands males do not in any way represent the general male population. But things get more problematic:
1. Sperm counts are changed by smoking and obesity. No data on these variables was available.
2. Couples who can’t conceive for years and years often have considerable stress and higher rates of anxiety and depression.
3. There’s no control group.
4. The assumption is that the criteria from center to center are similar and have not changed over the years. Many clinicians and researchers think that’s poppycock – how sperm are counted has changed materially over those 17 years in most clinical labs.
And many would argue that 50 million sperm per millileter is still above the standard threshold of 40 million felt necessary for high fertility rates.
But there’s a strange history behind all this.
The History of the Sperm Count
Until recently, study of population sperm counts has been something of a Scandinavian specialty. A famous paper in Lancet, emanating from Denmark, found that sperm counts had dropped by half from 1940-1990 – based on a literature search and meta-analysis of more than 60 studies.
But is it really that simple?
In turns out different countries have rather different sperm counts – assuming you are looking at similar populations.
One popular source for these studies are “volunteers” among military conscripts.
Denmark is part of NATO, Sweden is not. However, national conscription has taken place in both nations.
And the populations are genetically very similar – pretty much the same people. In southern Sweden, or Skane, there are only a few miles of water separating the two countries – now covered by a bridge. Southern Swedes are often chided by their northern compatriots for their ridiculously throaty provincial speech, “Danish” like and comically filled with grammatical “peculiarities.”
Even sensible Scandinavians have their differences.
So it was a bit of surprise to discover in 2002 that conscripts in Denmark had a sperm count 31% lower than that of Southern Swedes. Sweden also has a testicular cancer rate half of that of Denmark.
Was the higher sperm count related to the cause?
Some of the reliable data continues to come from similar aged Scandinavians draftees. One of the more interesting looked at comparisons between those conscripted in 2000 and 2010.
No differences were found. Sperm counts were a robust 78 million per millileter.
Yet other intranational comparisons show major changes. The French study that compared men whose partners were undergoing IVF was itself spurred by a 1995 paper looking at Parisians that found a 2% decrease in sperm counts year by year – the same as the recent IVF data.
However, virtually nowhere in the literature are there comparisons over time of the same men. Nor are there large, reasonably similar general population cohorts accessed over decades using the same canvassing and laboratory techniques.
In several studies of mainly developed nations, sperm counts among older males have been dropping through the decades. If the laboratory techniques used were comparable, this may speak to worsened overall health.
Yet obesity and smoking do not aid health anywhere in the body – including the reproductive tract. Other factors that affect sperm number, including near ubiquitous pollutants like BPA, are also not good for public health. And these and other social and biological variables may have a lot to do with the highly varied testicular cancer rates seen throughout the world.
But despite media outcry, French and Scandinavian men still appear to have sufficient sperm counts for normal fertility.
That should be worth a lot.
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