The latest research suggests that guys can relax about the state of their swimmers. One of more popular scares of the 1990s was the threat that environmental estrogens allegedly posed to male fertility. The idea is that various man-made substances act like estrogen in the human body and were possibly responsible for as much as a 50 percent average decline in sperm counts since the World War II. One of the groups reporting this alarming trend was led by Danish researcher Niels Skakkebaek.This concern was hyped in the 1996 environmentalist screed Our Stolen Future: Are We Threatening Our Ferility, Intelligence, and Survival?—A Scientific Detective Story by activsts Theo Colborn, Dianne Dumanoski, and John Peterson Myers.
Back in 1996, I wrote an op/ed, "Hormones and Humbug: A New Expose is One Part Pseudo-Science, Two Parts Hype, Three Parts Hysteria" for the Washington Post analyzing the claims made in Our Stolen Future. Here's some of what I reported:
Like most thrillers, "Our Stolen Future" is based on a little bit of fact and a whole lot of imagination.
Are these synthetic chemicals really causing hormonal harm? Most scientists don't think so. John Giesy, a professor of toxicology at Michigan State University and past president of the Society of Environmental Toxicology and Chemistry, says, "Frankly, Colborn doesn't know very much. She reads the entire literature and picks and chooses things that support her preconceived views."
Stephen Safe, a professor at Texas A&M University and a leading expert on environmental estrogens, agrees: "If you look at the book carefully, it's a very unscientific presentation."
The first thing that must be noted is that we are exposed to vastly greater quantities of natural estrogens than we are to synthetic estrogens. Why? Because common food plants like soybeans, corn, wheat, broccoli and kidney beans are loaded with natural estrogens. People eat 40 million times more natural plant estrogens than they do synthetic estrogens each day. Synthetic estrogens are thousands to millions of times weaker than the estrogen produced by the body. Colborn acknowledges this but suggests that synthetics are more pernicious "because they can persist in the body for years, while plant estrogens might be eliminated within a day."
Like so much of "Our Stolen Future," this is true, but misleading. Giesy points out that estrogen compounds must be circulating in the blood to have an effect. And even if the body does eliminate plant estrogens daily, each meal replenishes the amount circulating in our blood. In fact, synthetics are generally inactive because they are stored in the body's fat cells. More importantly, the levels of the chemicals that worry the authors have been dropping for decades. For example, background DDT levels in the United States are only one-15th to one-20th of what they were in the 1970s. As for PCB levels, they have also declined. In 1972, 61 percent of Americans had 1 part per million of PCB in their fat tissues; by 1983, only 6 percent did.
The most sensational assertion in "Our Stolen Future" is that human sperm counts have fallen by 50 percent in the last 50 years, a trend that the authors suggest may jeopardize the very future of the human race. This claim is largely based on an analysis of 61 studies by Danish scientist Niels Skakkebaek and his colleagues. Most fertility specialists regard Skakkebaek's study as severely flawed. Among other things, he did not take into account regional differences, age differences and ethnic differences in sperm donors. Last November, Dr. Larry Lipshultz, professor of urology at Baylor College of Medicine, co-chaired a "consensus meeting" attended by leading fertility researchers including Skakkebaek. "We reviewed all available data and concluded that you really cannot use these data to draw the conclusions that Colborn has drawn about trends in the quality of human semen," says Lipshultz.
A forthcoming study in the scholarly journal Fertility and Sterility further undercuts the notion that sperm counts are declining. Dr. Harry Fisch, who heads the male reproductive center at Columbia Presbyterian Hospital in New York, looked at trends in sperm counts in New York City, Minnesota and Los Angeles and found that there has been no nationwide change in semen quality in the last 25 years. In another study, researchers in Wisconsin found no change over a 10-year period.
Colborn also suggests that infertility is increasing in the United States. But it's not so. Dr. Richard Sherins of the Genetics and IVF Institute in Fairfax wrote in the New England Journal of Medicine that "rates of infertility have remained constant during the past three decades (at 8 to 11 percent), and male infertility has accounted for approximately one-third of the cases." …
Baylor College of Medicine's Lipshultz puts it succinctly when he says that, "Something is missing in 'Our Stolen Future' and that's called science." He adds, "The book is going to frighten a lot of people and that's unfair."
Striving for some brevity, I will not cite the section of my op/ed in which I debunked the claim that environmental estrogens were responsible for increasing cancer rates.
Nearly twenty-five years after this book helped launch numerous regulations, new data is showing that with respect to claims about a sperm apocalypse the environmental estrogen hypothesis turns out to be exaggerated. In today's New York Times, Gina Kolata reports:
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.
So what does the new Danish study (downloadable here) find:
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. These data were publicly presented for the first time in March of this year, when they were posted on a government agency Web site by the Danish National Board of Health. These data provide no indication that semen quality has changed during the past 15 years (Fig.). Throughout the years of surveillance, the crude median sperm concentration has fluctuated around a median value of 40 – 45 million/mL, with the lowest value (35 million/mL) in 2006 and the highest (50 million/mL) in 2007.
No decline since 1996. The researchers are appropriately cautious and do note that "the proportion of young men with low sperm counts is surprisingly large." However, they point out:
How do the new findings fit with concerns regarding environmental effects on male reproduction? A substantial research effort in the past 15 years has uncovered numerous environmental chemicals that weakly interfere with endoge- nous hormonal regulation through a variety of mechanisms related to steroid receptors and various enzymes. The estrogen hypothesis proposed in the early 1990s has been largely abandoned by one of its fathers, and is not supported by a wide range of epidemiologic data. Meanwhile, there is only very limited epidemiologic evidence to support the broader endocrine disruption hypothesis (delayed effects on the male reproductive system following imbalance of estrogenic and androgenic actions in early fetal life, for instance, as might be caused by phthalate exposure).
So if environmental estrogens are unlikely culprits, what could account for some young men having relatively low sperm counts? The researchers suggest that the recent increase in obesity might be a contributor.
Interestingly, Skakkabaek is one of the lead researchers on this new study and has apparently been reluctant release these findings.
Whole New York Times article can be found here.