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Declining Sperm Counts? Long View is there is too much uncertainty

2016-01-12

Here’s another “decline of the West” type of factoid: some scientists are beginning to believe that sperm counts have been going down over the last fifty years.  Not low enough, on average, to cause infertility, but going down.  It is controversial because counting sperm has always been difficult and subject to alteration by changes in method, but many studies are pointing towards declining counts.

The first big study we have is here: http://www.ourstolenfuture.org/newscience/reproduction/sperm/2000swanetal.htm  This is a survey of a large number of primary studies gathered together from 1934-1996.  The final conclusion, after looking at 101 studies, was that the declines in sperm count are real.  It goes on to mention the increases in testicular cancer and cryptorchidism that have occurred during the same time period.  The study says at the end that environmental exposures are probably responsible for this increase, although it doesn’t mention any specific exposure.

The numbers were 113 million per milliliter in 1940 and 66 million/ml in 1990.

In 2012, a French study reported in the journal Human Reproduction concluded that there had been a significant decline in sperm count over the seventeen year period from 1989 to 2005; the numbers were 73.6 million per milliliter in 1989 and 49.9 million/mil in 2005.

A contrary study from 1996 showed sperm counts of 72.7 million/ml in California, 100.8 million/ml in Minnesota, and 131.5 million/ml in New York.

Another review concluded that there was no over all decline in sperm count based on a large number of studies done over the period from 1950 to 2000; six studies showed declines, sixteen did not, and five were ambiguous.  More importantly, the studies that did not show declines totaled 100,000 subjects and the ones that did show declines only totaled 10,000.  Counts varied dramatically based on country studied.

So the most we can say is that there may have been decreases in France, Israel, Greece, Denmark, and Italy, and no decreases in the United States, Denmark, Canada, Spain, Slovenia, Korea, and possibly Japan.  Contradictory results were found in Denmark and France (Paris vs. Toulouse.), and in Israel.  Eight of the studies that failed to find decreases had less than a thousand subjects, but three (Canada, Spain, and Korea) were very large.  In contrast, all but one of the positive decrease studies had over a thousand subjects.  Three of the ambiguous studies were over five thousand, including one each in Denmark and France.

There has, however, been a decline (in the United States) in serum testosterone concentrations, and it has been suggested that this is due to increasing obesity.

A study of eighteen year old men having their military physicals in Denmark showed no decline in sperm counts.   Unfortunately, the study was never actually published; the data was presented on a web site by the Danish Ministry of Health.  This study, of 5,000 men over fifteen years, seems to be the most convincing research yet done, and it is negative.

A comprehensive review published in February 2014 concluded that there is no definite evidence of an overall decline in sperm counts nor a definite sign of an “endocrine disrupter” lowering counts.  The review examined epidemiological studies published from 1985 to 2013 and found “no[t] enough evidence to confirm a worldwide decline in sperm counts” and “no scientific truth of a causative role for endocrine disruptors” because of mixed evidence: some studies show a decline, but most do not.  The authors of this review emphasize the difficulties in producing reliable counts over long periods of time due to variations in methods and analyses, and especially due to large variations in sperm quality and quantity.  There is considerable variation simply from one geographic region to another.

Our conclusion is that there is no definite evidence of a decline in sperm count over the years; it will be necessary to continue large, long-term studies to see if there are any definite variations in the future.  This aspect of the “decline of the West” is ambiguous, to say the least.

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