The Demise of Human Sperm

John Robbins | 11/05/02

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They Can Sow, But They Can't Reap

In Diet For A New America I stated that we are witnessing a dramatic decline in human sperm quantity and quality. If this is true, it is obviously of foremost importance. While it is true that only one sperm is required to fertilize an egg, once sperm counts drop below a certain point infertility becomes increasingly common.

While skeptics and representatives of the chemical industry have attacked Diet For A New America, and said sperm counts are not really dropping, developments since the book was published in 1987 have not been reassuring.

A 1992 study in the British Medical Journal found that men in western countries today have less than half the sperm production their grandfathers had at the same age.1 The report examined 61 separate studies of sperm count in men in many countries, including the U.S., and concluded that there has been a 42% decrease in average sperm count, from 113 million per milliliter (ml) to 66 million per ml, since 1940. (There are 4.5 milliliters in a teaspoon). Furthermore, the average volume of semen diminished from 3.4 ml to 2.75 ml, a 20% loss since 1940. Thus the average man has lost 53% of sperm production in the last 50 years.

How low can sperm counts drop before men become infertile? In many instances, men are considered infertile if their sperm counts drop as low as 20 million per ml, although it is still possible for a man with that sperm count to sire a child if other factors are all favorable. If sperm count drops much below that, however, reproduction becomes increasingly unlikely. Below 5 million, a man is definitely sterile.

Diminished sperm count is not the only factor in male sterility. If sperm quality is compromised, higher sperm counts are needed for reproduction to take place. As sperm motility (the ability of the sperm to move) is impaired, the sperm may be unable to pass through the cervical mucous or penetrate the hard outer shell of the egg. When sperm motility is reduced, sperm become increasingly incapable of fertilizing the egg.

Abnormally shaped sperm also have difficulty fertilizing an egg. In one study, if 14% or more of sperm had round enlarged heads (indicating early unraveling of genetic material) the chances for pregnancy fell to about 20%.2

It appears increasingly certain that in today's world both the quantity and quality of male human sperm are declining. The New England Journal of Medicine reported in 1995 that not only had sperm count declined 33% during the past 20 years among fertile, healthy men in Paris, France, but also that, during the same period, the proportion of motile sperm (sperm able to swim) declined at the rate of 0.6% per year, and the proportion of normally shaped sperm (compared to misshapen sperm) declined at the rate of 0.5% per year.3

We now have a scientific consensus that both sperm counts and the quality of sperm are declining. Yet the chemical industry has only stepped up its efforts to convince the public and elected officials that the data is too ambiguous and controversial to justify alarm. To do so, they point to possible "confounding factors," such as subject abstinence time before sampling, and differing methods of analysis, that can influence the accuracy of sperm count data. Their tactic is to take legitimate but relatively minor issues and blow them out of all proportion to imply that nothing conclusive has been learned.

In 1999, however, the journal BioEssays published a major report by University of Missouri epidemiologist Shanna Swan that found the dramatic decline of average sperm density in the U.S. and Western Europe to be even greater than previously estimated.4 In a meta-review of data from more than 60 studies, Swan found that average sperm counts among healthy American men dropped from 120 million sperm per milliliter of semen in 1938 to just over 50 million in 1988. In Europe, she found, sperm counts dropped to roughly the same level, and have been dropping by the staggering rate of 3.1% each year between 1971 and 1990.

Despite the efforts of the Chemical Manufacturer's Association, Monsanto, DuPont, etc., to cloud the issue, the evidence of declining sperm levels continues to mount. It was the New Yorker Magazine that, in 1961, first published Rachel Carson's Silent Spring. In 1996, the New Yorker Magazine ran a long feature story called "Silent Sperm."5 The author, Lawrence Wright, interviewed dozens of prominent researchers in the field of endocrinology and reproductive health and made some interesting points:

  1. Danish endocrinologist Niels E. Skakkebaek said it has become difficult for sperm banks to establish a core of donors. In some areas of Denmark, for example, they are having to recruit ten potential donors to fine one with good semen quality.
  2. Skakkebaek also reported that 84% of the Danish men he studied had sperm quality below the standards set by the World Health Organization.
  3. There has been a three-fold increase in men whose sperm count is below 20 million, the point at which fertility is jeopardized.
  4. Researchers at the Washington Fertility Study Center report that the sperm counts of their donors, largely medical students, have suffered a steady decline for many years, to the point that the researchers are now worried that, if the decline continues at the same rate, by the year 2002 there will be no potential donors who can meet the approved or recommended standards.
  5. The fact is that the number of morphologically normal sperm (meaning sperm with a normal shape) produced by the average man has dropped below the level of those of a hamster, which has testicles a fraction the size of a man's.

Why is all this happening? The prevailing explanation implicates environmental chemicals called endocrine disrupters that masquerade as hormones. Specifically, synthetic chemicals that mimic the female sex hormone estrogen may influence male development in utero or during the formative years of early childhood when hormone sensitivity is high.

In 1993, a study published in The Lancet traced the decline to males being exposed in the womb to female sex hormones that permanently alter their sexual development, and greatly reduce a man's ability to produce sperm.6 The study, along with one published later in 1993 in the Journal of Endocrinology established several diet-linked sources of increased estrogenic exposure to males in the womb:7

  1. The modern diet increases the levels of natural estrogen in women. Fiber in the diet today is lower than it was 50 years ago. Natural estrogens excreted in the bile are more readily reabsorbed into the bloodstream when the lower intestine contains little dietary fiber. Thus, a fetus today may be exposed to higher levels of the mother's own natural estrogens, compared to a fetus 50 years ago. (Fiber is found in all whole grains, vegetables and fruits; and is absent in all meats, dairy products, and eggs.)
  2. Another source of increased estrogens in women today is the many synthetic organic chemicals and heavy metals that have been released into the environment in massive quantities since world war II. Some of these compounds, such as PCBs and dioxins, concentrate in ever higher levels on higher rungs of the food chains. Vegetarians, and even more notably vegans, thus enjoy some degree of protection.
  3. A study published in The Lancet in 1994 found that organic farmers had much higher sperm counts than farmers using chemicals.8

Many animals produce up to 1,400 times as much sperm as is needed for fertility.9 Human males are not nearly so prolific. The average human male produces only five or six times as much sperm as is needed for fertility. In the best of circumstances, humans don't have much sperm to spare.

To summarize, in the last 50 years, the sperm count of the average American male has dropped from 120 million sperm per milliliter of semen to just over 50 million, and there have been losses in sperm quality that markedly enlarge the impact and significance of these reductions. At levels of 20 million, many men experience an inability to reproduce, but with the decline in sperm motility and in normally shaped sperm we may in the future see higher sperm counts needed for fertility. Meanwhile, sperm counts continue to drop. At what point will our elected officials wake up?

In recent years, we have seen the tobacco industry defend its products by trying to create a smokescreen of controversy -- and the result has been millions of deaths to lung cancer, emphysema, etc. Now we are seeing the chemical industry doing the same thing, only the result may eventually come to jeopardize the survival not just of countless individuals, but of our species itself.

1. Elizabeth Carlsen and others, "Evidence for decreasing quality of semen during the past 50 years," British Medical Journal Vol 305, 1992, pgs 609-613
2. "Infertility In Men," Sept 1998;
3. 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
4. Brian Halweil, "Sperm Counts Are Dropping" World Watch, March/April, 1999, pgs 32-33 Rochelle Jones, "Is the Environment Hurting Men?", January 3, 2000
5. Lawrence Wright, "Silent Sperm" the New Yorker Magazine, January 15, 1996
6. 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
7. R.M. Sharpe, "Declining sperm counts in men ? is there an endocrine cause?" Journal of Endocrinology, Vol 136, 1993, pgs. 357-360
8. Annette Abell and others, "High sperm density among members of organic farmers' association," The Lancet, Vol 343, June 11, 1994, pg 1498
9. Peter K. Working, "Male Reproductive Toxicology: Comparison of the Human to Animal Models," Environmental Health Perspectives, Vol 77, 1988, pgs 37-44


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