In Update on Sperm, Data Show No Decline
http://www.nytimes.com/2011/06/07/health/research/07sperm.html?_r=1
By GINA KOLATA
Published: June 6, 2011
It is one of the most fraught topics in environmental health. Are men becoming less fertile, with declining sperm counts and diminishing sperm quality? If they are, then sperm might be an early warning sign of environmental dangers. And the prime suspects have been substances like plastics and pesticides that can have weak estrogenlike effects on cells.
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.
Many other researchers criticized the data’s quality, citing flaws like a lack of standardized methods of collecting semen, methodological issues in semen analysis, biases in the ways men were selected, and variations in the length of time men abstained from ejaculating before their semen was collected.
The study, said Dolores Lamb, a fertility expert at Baylor College of Medicine and president-elect of the American Society of Reproductive Medicine, “was problematic and raised alarms in society without critical thinking about the caveats and weaknesses inherent in the data and its analysis.”
Nonetheless, the paper was highly influential. It was cited by 1,000 subsequent scientific papers.
Other researchers soon published their own studies, but methodological problems persisted. And the later studies came to contradictory conclusions, with some saying sperm counts were declining and others saying they were not. The result was a body of evidence so poor that a panel of experts assembled by the National Academy of Sciences in 1999 said its members could not come to a consensus on whether counts were declining, mostly because of seriously flawed studies.
Meanwhile, the same Danish group that got the debate started began a study that analyzed annual semen samples collected from 18-year-old men who were being examined for their fitness for the military — a requirement in Denmark. Over the past 15 years, a total of 5,000 men provided semen for analysis.
That design was an improvement over older studies, Dr. Lamb said. The data are from men of the same age and from one geographic area (sperm numbers and quality can vary from one region to another). Analysis of sperm is better now than it was in years past. And with 15 years of data, she said, any decline in sperm numbers or quality should have been evident.
The problem was that the group did not publish its data, even though, said Dr. Jens Peter Bonde, a fertility researcher at Copenhagen University Hospital, “we have asked for these findings — they are of great public interest.” Dr. Niels Erik Skakkebaek of the University of Copenhagen, who initiated the study, said he wouldn’t comment on the data before the research appears in a scientific journal. And he would not say when that might be.
But the data have been published anyway, in an unusual manner.
In a telephone interview, Dr. Skakkebaek said the research group’s current leader, Niels Jorgensen, sent the data to the Danish Ministry of Health, which helped pay for the study, and the ministry then posted the data on its Web site. Dr. Skakkebaek was angry, saying in an e-mail: “The trend data has not been appropriately scientifically scrutinized. Also, I cannot guarantee that the civil servant in the ministry put our data into the figure without mistakes.”
Now, an American journal, Epidemiology, has published the data in a commentary and discussed them in an editorial.
The commentary, by Dr. Bonde, includes a graph of the data and says they constitute “the best longitudinal semen data yet available.”
The journal’s editor, Dr. Allen Wilcox, said he decided to reproduce the figure from the ministry Web site because the data are so important. Yet, he wrote in the editorial, “the presentation of a few raw data on a Web site — or in a commentary — is hardly the preferred way to advance science.” But, he added, “neither is it acceptable for valuable data to be held in storage.”
Wilcox AJ. On Sperm Counts and Data Responsibility. Epidemiology.
Bonde JP, Ramlau-Hansen CH, Olsen J. Trends in Sperm Counts: The Saga Continues. Epidemiology.
http://www.nytimes.com/2011/06/07/health/research/07sperm.html?_r=1
By GINA KOLATA
Published: June 6, 2011
It is one of the most fraught topics in environmental health. Are men becoming less fertile, with declining sperm counts and diminishing sperm quality? If they are, then sperm might be an early warning sign of environmental dangers. And the prime suspects have been substances like plastics and pesticides that can have weak estrogenlike effects on cells.
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.
Many other researchers criticized the data’s quality, citing flaws like a lack of standardized methods of collecting semen, methodological issues in semen analysis, biases in the ways men were selected, and variations in the length of time men abstained from ejaculating before their semen was collected.
The study, said Dolores Lamb, a fertility expert at Baylor College of Medicine and president-elect of the American Society of Reproductive Medicine, “was problematic and raised alarms in society without critical thinking about the caveats and weaknesses inherent in the data and its analysis.”
Nonetheless, the paper was highly influential. It was cited by 1,000 subsequent scientific papers.
Other researchers soon published their own studies, but methodological problems persisted. And the later studies came to contradictory conclusions, with some saying sperm counts were declining and others saying they were not. The result was a body of evidence so poor that a panel of experts assembled by the National Academy of Sciences in 1999 said its members could not come to a consensus on whether counts were declining, mostly because of seriously flawed studies.
Meanwhile, the same Danish group that got the debate started began a study that analyzed annual semen samples collected from 18-year-old men who were being examined for their fitness for the military — a requirement in Denmark. Over the past 15 years, a total of 5,000 men provided semen for analysis.
That design was an improvement over older studies, Dr. Lamb said. The data are from men of the same age and from one geographic area (sperm numbers and quality can vary from one region to another). Analysis of sperm is better now than it was in years past. And with 15 years of data, she said, any decline in sperm numbers or quality should have been evident.
The problem was that the group did not publish its data, even though, said Dr. Jens Peter Bonde, a fertility researcher at Copenhagen University Hospital, “we have asked for these findings — they are of great public interest.” Dr. Niels Erik Skakkebaek of the University of Copenhagen, who initiated the study, said he wouldn’t comment on the data before the research appears in a scientific journal. And he would not say when that might be.
But the data have been published anyway, in an unusual manner.
In a telephone interview, Dr. Skakkebaek said the research group’s current leader, Niels Jorgensen, sent the data to the Danish Ministry of Health, which helped pay for the study, and the ministry then posted the data on its Web site. Dr. Skakkebaek was angry, saying in an e-mail: “The trend data has not been appropriately scientifically scrutinized. Also, I cannot guarantee that the civil servant in the ministry put our data into the figure without mistakes.”
Now, an American journal, Epidemiology, has published the data in a commentary and discussed them in an editorial.
The commentary, by Dr. Bonde, includes a graph of the data and says they constitute “the best longitudinal semen data yet available.”
The journal’s editor, Dr. Allen Wilcox, said he decided to reproduce the figure from the ministry Web site because the data are so important. Yet, he wrote in the editorial, “the presentation of a few raw data on a Web site — or in a commentary — is hardly the preferred way to advance science.” But, he added, “neither is it acceptable for valuable data to be held in storage.”
Wilcox AJ. On Sperm Counts and Data Responsibility. Epidemiology.
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.
Bonde JP, Ramlau-Hansen CH, Olsen J. Trends in Sperm Counts: The Saga Continues. Epidemiology.
Almost 20 years ago, a longstanding debate over possible declines in sperm counts was reignited by a paper in BMJ, claiming that sperm counts had declined worldwide by 50%.1 Despite its rather weak documentation, this paper by Carlsen et al had a strong impact in the public media, and has been cited in more than 1000 scientific papers— perhaps in part because the authors were bold enough to include a linear regression line pointing forward toward continuing declines and a doomed society. Since the publication of that paper, numerous studies have reported secular trends and geographical shifts in sperm counts, with conflicting findings and no emerging consensus. However, recent developments may be changing this picture.