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Falling sperm counts are linked to endocrine-disrupting chemicals

REUTERS/Edgar Su

A report lists environmental pollution — particularly so-called endocrine disruptors, which can act like estrogen in males — as the most prominent explanation for this widespread, 38-year-long decline, which one expert is calling “a death spiral of infertility in men.”

A startling new review of sperm production finds that men throughout most of the industrialized world have seen, in aggregate, a 52 percent decline in sperm count over the last generation and a half  — with exposure to endocrine-disrupting environmental pollution the probable cause.

A sweeping meta-analysis of data from nearly 200 individual studies, the research does not directly attribute the decline to any particular cause, and it notes that many factors are capable of driving down sperm production, especially in the short term.

However, it lists environmental pollution — particularly so-called endocrine disruptors, which can act like estrogen in males — as the most prominent explanation for this widespread, 38-year-long decline, which one expert is calling “a death spiral of infertility in men.”

The team, led by Hagai Levine of Hadassah-Hebrew University in Jerusalem, reviewed more than 2,500 articles reporting primary data on sperm counts in men around the world. After excluding research on men selected for study because they were known to have fertility problems, or factors specifically associated with lower sperm production, they assembled for meta-analysis a set of 185 studies of nearly 43,000 men who gave samples between 1973 and 2011.

From these results, they calculate that sperm counts declined by 50 to 60 percent among men in North America, Europe, Australia and New Zealand. Men in South America, Africa and Asia did not show comparable declines, but the authors explain that data for these regions was not comparable in quantity or quality, especially before 1985.

In addition to the obvious problem of reduced fertility, their paper notes that lowered sperm counts are associated with a variety of medical conditions, pointing to a likelihood of diminished health and a shorter lifespan.

As for the probable causes of such a steep decline, the authors say

While the current study is not designed to provide direct information on the causes of the observed declines, sperm count has been plausibly associated with multiple environmental and lifestyle influences, both prenatally and in adult life. In particular, endocrine disruption from chemical exposures or maternal smoking during critical windows of male reproductive development may play a role in prenatal life, while lifestyle changes and exposure to pesticides may play a role in adult life. Thus, a decline in sperm count might be considered as a ‘canary in the coal mine’ for male health across the lifespan. Our report of a continuing and robust decline should, therefore, trigger research into its causes, aiming for prevention.

The sheer scope of the data gathered for analysis here would seem to address neatly the objections of some skeptics of sperm-count decline  — including, for one recent example, the cancer epidemiologist Geoffrey Kabat, writing in Forbes a few months ago  — that sperm-count studies are too small or narrow to reliably factor out the  normal variability that occurs from place to place and time to time, in response to all kinds of environmental influences and individual behaviors.

Exposure across generations

Published on Tuesday in the journal Human Reproduction Update, the study follows by one week another study which apparently  — and amazingly  — is the first to test for cumulative endocrine-disruption effects from chemical exposure across successive generations.

The study looked at sperm production and abnormalities of the reproductive tracts in male mice. Its chilling conclusion: The impacts are worse in the second generation than the first, and worse still in the next, with some third-generation mice producing no sperm at all.

Though potentially more significant, in my view, this paper has gotten far less attention than the Levine research; I first saw it referenced in Environmental Health News in a piece by Pete Myers, a Ph.D. biologist who co-wrote the early and influential book on endocrine disruption, “Our Stolen Future,” published in 1996.

Myers is the founder and chief scientist at EHN, a daily online publication that does original reporting on environmental health science while aggregating, annotating and critiquing reporting done elsewhere. In his view, the two studies taken together mean “you should be worried — and your kids should be terrified.”

The intergenerational study was published last Thursday in the journal PLOS Genetics, and looked at abnormalities in the reproductive tracts of male mice and two generations of their male offspring. It aimed to answer what lead researcher Tegan Horan, a doctoral student at Washington State University told Myers she saw as “a simple question with real-world relevance that had simply never been addressed."

Here is Myers’ terse summary of the research context:

Since World War II, successive generations of people have been exposed to a growing number and quantity of environmental estrogens — chemicals that behave like the human hormone estrogen. Thousands of papers published in the scientific literature (reviewed here) tie these to a wide array of adverse consequences, including infertility and sperm count decline.

This phenomenon — exposure of multiple generations of mammals to endocrine disrupting compounds — had never been studied experimentally, even though that's how humans have experienced EDC exposures for at least the last 70 years. That's almost three generations of human males….

More than a dozen papers have now been published on "trans-generational epigenetic inheritance," where exposure in a great-grandmother causes adverse effects in great-grandson — without further exposures and without changes in DNA sequence. But crucially these experiments typically only expose one generation — the first — rather induce ongoing exposures across generations, which is the reality of human experience.

Other scientists respond

Reaction to the Levine study has been positive, both on the quality of its findings and their importance, with many in the scientific community endorsing its tentative attribution of the problem to environmental exposure.

Allen Pacey, an andrologist at Britain’s Sheffield University, told the BBC that "I've never been particularly convinced by the many studies published so far claiming that human sperm counts have declined in the recent past. However, the study today by Dr Levine and his colleagues deals head-on with many of the deficiencies of previous studies."

Frederick vom Saal, Curators’ Distinguished Professor Emeritus of Biological Sciences at the University of Missouri, told Myers that "the study is a wakeup that we are in a death spiral of infertility in men."

And Enrique Schisterman of the National Institutes of Health, where he serves as chief of the epidemiology branch at the National Institute of Child Health and Human Development, told Time magazine that Levine’s work represented a significant advance and pointed to “a serious problem.”

I think there is a consensus in the scientific community that if the results are real, it has to be an environmental factor. Genetics would not explain such a rapid decline.

* * *

Both papers can be read and downloaded without charge; the Levine paper on sperm counts is here and the Horan paper on reproductive abnormalities in successive generations is here.

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