=======================Electronic Edition========================
RACHEL’S ENVIRONMENT & HEALTH WEEKLY #432
—March 9, 1995—
News and resources for environmental justice.
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TWO MORE STUDIES SHOW HUMAN SPERM LOSS
Two new studies have found that sperm count in men has declined
precipitously over the past 20 years. [1] 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. [2] 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. [3] 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. [4]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. [5]
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 declined simultaneously.
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. [6] Such abnormalities have doubled in
frequency during the past 30 years in many parts of the world. [7]
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. [8] 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 pollution.”
                
                
                
                
    
–Peter Montague
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[1] 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.