Two new studies have found that sperm count in men has declined
precipitously over the past 20 years. Sperm count is the number of
sperm in each cubic centimeter of semen. The NEW ENGLAND JOURNAL OF
MEDICINE reported last month that sperm count has declined 33% during
the past 20 years among a study-population of 1351 healthy, fertile men
in Paris, France. A briefer report in the BRITISH MEDICAL JOURNAL last
summer found that, comparing men of similar ages, sperm count in 3729
Scottish men had declined 41% among those born in 1969 compared to
those born in 1941.
In 1992, a historical analysis of 62 separate sperm-count studies, by
Elisabeth Carlsen, concluded that sperm count among men throughout the
industrialized world has declined by about 50% during the past 50
years. In 1994 this finding was challenged by researchers who said
that it might have been caused by Carlsen's erroneous choice of
statistical methods, not by an actual decline in sperm count. The
two new studies appear to confirm the conclusion than an actual decline
in sperm count has occurred and is occurring.
No one knows what is causing the apparent decline in sperm count among
men. It is still possible that the decline is not real, that it results
from some unknown hidden bias in the 64 studies that have been
conducted so far. For example, these 64 studies may have examined men
who are not typical of the general population. And various factors that
influence sperm count may not have been fully accounted for. On the
other hand, it is entirely possible that the decline IS real. As
Carlsen and her co-workers said in 1994, defending their 1992
conclusion, "The most cautious conclusion that can be drawn from the
existing data is that semen quality has declined significantly between
1940 and 1990." Even if the decline is real, no one knows for sure what
might be causing it. Various hypotheses have been suggested.
The hypothesis getting the most attention is this one: something --
perhaps hormone-mimicking chemicals in the mother's blood --is
affecting male children before they are born. This hypothesis suggests
that male children are being born with fewer Sertoli cells --the cells
which, after puberty, cause the production of sperm. Reduced numbers of
Sertoli cells (and reduced sperm count) have been observed in the male
offspring of estrogen-exposed pregnant rats.
New Studies: Paris
The study-group in Paris consisted of 1351 healthy men who had donated
sperm to a sperm bank maintained by a hospital, starting in 1973. Each
of the men had fathered at least one child. One percent of the men were
farmers and 16 percent were manual laborers; 40 percent were classified
as "technicians" and 38 percent as "executives." From 1973 to 1992,
their average (mean) sperm count declined at the rate of 2.1 percent
per year, from 89 million per cubic centimeter (cc) to 60 million per
cc. During the same period, the proportion of motile sperm (sperm able
to swim) declined at a rate of 0.6 percent per year, and the proportion
of "normal" sperm (compared to misshapen sperm) declined at the rate of
0.5 percent per year. In sum, the quantity and quality of sperm
This study answers some of the concerns of some of the critics of
Carlsen's 1992 study. Those critics charged that abstinence from sex
causes an increase in sperm numbers and a decrease in sperm with good
motility and Carlsen could not control for that. The Paris study took
into account the length of abstinence before samples were taken. It
also controlled for age, and for year of birth. The decline in sperm
quantity and quality, linked to year of birth, was still observable
after controlling for length of abstinence and age.
Among the Paris group, a subgroup of 382 men in a narrow age range (28
to 37 years) was chosen for special analysis; they had all reported a
similar period of abstinence (3 to 4 days). Among this group, there was
a clear decline in sperm count from 1973 to 1992: from 101 million per
cc to 50 million per cc, a reduction by half. The average 30-year-old
born in 1945 would have a count of 102 million per cc; the average 30-
year-old born in 1962 would have a count of 51 million.
"We conclude that there has been a true decline in the quality of semen
during the past 20 years, since the characteristics of semen from a
fertile man of a given age in 1992 were significantly poorer than those
of a fertile man of the same age in 1973," the French researchers said.
New Studies: Scotland
The researchers in Scotland completed their study in response to
criticism of Carlsen's 1992 historical analysis of 62 sperm-count
studies, showing a 50% reduction in 50 years. They had records for 3729
semen donors born between 1940 and 1969 and they examined these by
statistical techniques chosen to avoid the (controversial) criticisms
that had been leveled at Carlsen's work. They found an apparent decline
in sperm count from 128 million per cc (in men born in the 1940s) to 75
million in men born in the late 1960s, a 41% loss. "Thus we do not
accept that the evidence for a fall in sperm concentrations is
unconvincing," they concluded.
Several researchers have noted that the decline in sperm quality
(count, motility and normal shape) coincides with an increasing
incidence of abnormalities of the male genital tract, including
testicular cancer and cryptorchidism (undescended testicles) in various
countries. Such abnormalities have doubled in frequency during the
past 30 years in many parts of the world. In Scotland, for example,
testicular cancer has doubled since 1960 and is striking a younger
population (ages 15 to 44) every year. The cause of these increasing
abnormalities remains a mystery.
One clue that may tie all the threads of evidence together is the
record of what happened to the sons of women who were given a synthetic
hormone, diethylstilbestrol (DES), during the 1950s and 1960s. About a
million American women were given DES as a "morning after" pill to
reduce the likelihood of pregnancy. Their sons have shown an increase
in genital tract abnormalities, AND reduced sperm count.
There is confirming data from animal experiments as well. Pregnant
female rats given a single, very low, dose of dioxin on the 15th day of
gestation, produce male offspring that have genital tract abnormalities
(particularly undescended testicles) and that have a low sperm count
after they mature. Dioxin does much of its toxic work by acting as
an estrogen-like hormone.
Thus, although it remains a hypothesis that estrogen-mimicking
chemicals are causing the observed changes in the male reproductive
tract, it is a hypothesis that is being taken very seriously by a large
number of scientists world-wide; they are working aggressively to
confirm its truth or falsehood.
It is, after all, an important matter for the future of the human
species. The reported sperm loss appears to be occurring world-wide.
The report in February in the NEW ENGLAND JOURNAL OF MEDICINE ends this
way: "The significant decline in the concentration of sperm during the
past 20 years in the Paris area may be related to an interaction of the
age of the [sperm] donors and the chronologic period [in which they are
living] that in turn could implicate factors affecting all the
inhabitants of an area, such as the water supply or environmental
 Jacques Auger and others, "Decline in Semen Quality Among Fertile
Men in Paris During the Past 20 years," NEW ENGLAND JOURNAL OF MEDICINE
Vol. 332, No. 5 (February 2, 1995), pgs. 281-285. And: D. Stewart
Irvine, "Falling sperm quality," BRITISH MEDICAL JOURNAL Vol. 309
(August 13, 1994), pg. 476.
 Elisabeth Carlsen and others, "Evidence for decreasing quality of
semen during past 50 years," BRITISH MEDICAL JOURNAL Vol. 305 (1992),
 Peter Bromwich and others, "Decline in sperm counts: an artefact of
changed reference range of 'normal'?" BRITISH MEDICAL JOURNAL Vol. 309
(July 2, 1994), pgs. 19-22. Elisabeth Carlsen and some of her co-
workers responded that Bromwich's analysis was "based on wrong
assumptions" and "failed to give any empirical reference that might
support [Bromwich's] assertion of differential selection." See Niels
Keiding and others, "Importance of empirical evidence," BRITISH MEDICAL
JOURNAL Vol. 309 (July 2, 1994), pg. 22.
 Richard J. Sherins, "Are Semen Quality and Male Fertility
Changing?" NEW ENGLAND JOURNAL OF MEDICINE Vol. 332 No. 5 (Feb. 2,
1995), pg. 327, says that studies conducted so far have not properly
controlled for differences in age, abstinence before semen analysis,
ejaculatory frequency, and the number of samples analyzed per person,
all of which can effect sperm count. Another author who has registered
skepticism of the 1992 findings is Stephen Farrow, "Falling sperm
quality: fact or fiction?" BRITISH MEDICAL JOURNAL Vol. 309, No. 6946
(July 2, 1994), pgs. 1-2.
 A. Giwercman and N.E. Skakkebaek, "The human testis--an organ at
risk?" INTERNATIONAL JOURNAL OF ANDROLOGY Vol. 15 (1992), pgs. 373-375.
And: Richard M. Sharpe and Niels E. Skakkebaek, "Are oestrogens
involved in falling sperm counts and disorders of the male reproductive
tract?" THE LANCET Vol. 341 (May 29, 1993), pgs. 1392-1395. And: R. M.
Sharpe, " Declining sperm counts in men --is there an endocrine cause?"
JOURNAL OF ENDOCRINOLOGY, Vol. 136 (1993), pgs. 357-360.
 A. Giwercman, cited above in note 5; and see Peter Boyle and
others, "Changes in Testicular Cancer in Scotland," EUROPEAN JOURNAL OF
CANCER AND CLINICAL ONCOLOGY Vol. 23 (1987), pgs. 827-830. And: A.
Giwercman and others, "Evidence for increasing evidence of
abnormalities of the human testis: a review," ENVIRONMENTAL HEALTH
PERSPECTIVES Vol. 101, Supplement 2 (1993), pgs. 65-71.
 See Sharpe and Skakkebaek, cited above in note 5.
 Thomas A. Mably and others, "IN UTERO and Lactational Exposure of
Male Rats to 2,3,7,8-Tetrachlorodibenzo-P-dioxin. 3. Effects on
Spermatogenesis and Reproductive Capability." TOXICOLOGY AND APPLIED
PHARMACOLOGY Vol. 114 (May, 1992), pgs. 118-126.
Descriptor terms: sperm count; fertility; human health; human
reproduction; reproductive system; new england journal of medicine;
british medical journal; scotland; france; sperm quality; semen
quality; hormones; estrogen;
PUBLIC INTEREST SCIENCE CONFERENCE APRIL 7-9
The 1995 Public Interest Science Conference (PISC) will be held April
7-9, 1995, at the University of Oregon in Eugene. This year the
conference will include workshops such as "Scientists Working With
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"Scientists, Emotion, and the Public Interest" (led by Mary O'Brien);
"Certainty in Science and Public Policy" (led by Peter Montague); and
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Registration for the conference costs $50.00 for professionals and
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Susan Shannon, Biology Department, U. of Oregon, Eugene, OR 97403.
Email queries to: email@example.com. This promises to be a
Descriptor terms: conferences; public interest science; ethics;