Call it the mystery of the missing sperm. It seems that men are not making as much sperm as their forefathers did. Indeed, sperm production appears to be in a tailspin.
In 1929, when scientists began keeping track of sperm production, they estimated that the average fertile male produces between 100-120 million sperm per milliliter of ejaculate.
By the 1950s, researchers found that sperm output was down to 80 million per milliliter. In recent years, it has slipped to between 60-70 million per milliliter. (The average ejaculation contains between two and five milliliters of semen.)
“A good majority of men would be considered below normal if they were measured against 1929 standards,” says Claude Gagnon, a professor in the division of urology at McGill University in Montreal.
Some researchers, however, doubt the accuracy of the sperm estimates, which were derived from studies of relatively small groups of men. Others say, who cares? After all, it takes only one spermatozoon to fertilize an egg.
And so far, there is no evidence that the species is having any trouble reproducing itself. Still, Prof. Gagnon and others believe there is cause for concern: “We should try to find out what’s happening.”
Is Pollution Making Men Less Fertile?
For want of a better explanation, some researchers suggest that pollution could be responsible. “Certainly, compared to 1929, the air is less healthy today,” says Dr. Jerald Bain, an endocrinologist at Mount Sinai Hospital in Toronto. “It’s not unreasonable to assume that environmental factors are involved.”
But what factors? People are exposed to a host of substances in varying quantities throughout their lives. “The fact, is we don’t have the answers,” acknowledges Dr. Bain.
To add to the confusion, scientists lack a complete picture of how sperm production may have changed over the decades. The absolute numbers may, indeed, have plummeted. But quality also counts. Abnormal or defective sperm are unable to carry out their prime function. And much can go wrong. Some sperm, which normally look like microscopic tadpoles, have two heads. Others lack the ability to “swim” to the site of the egg, or they are such slowpokes that they arrive too late.
Only within recent years have researchers fine-tuned their techniques for identifying and quantifying abnormal sperm. That means that much of the data gathered in the earlier part of this century is useless for purposes of comparison.
Dr. Art Leader, director of the GOAL program for assisted reproductive technology at the Ottawa Civic Hospital, notes that more and more couples are waiting longer to have their first child, which contributes to reproductive difficulties.
Is Fertility Really on the Decline?
However, there is no hint that overall fertility is on the decline. Between 1980-’81, the U.S. Congress’ Office of Technology Assessment did a study to gauge infertility in the U.S. It concluded that between 8 and 10 per cent of couples were infertile – that is, they were unable to achieve a pregnancy after one year of unprotected sex.
When the U.S. government agency carried out the same study between 1990-’91, the results were the same. “If men are getting less fertile, then women must be getting more fertile to compensate – and I don’t believe that is the case,” says Dr. Leader.
As a general rule, 40 percent of fertility problems are attributable to the male, 40 percent to the female and 20 percent to a combination of the male and female.
Studies carried out in developing countries have also shown wild fluctuations in sperm production without any threat to overall fertility. “In China, they have lower sperm counts because they have smaller testes. If they are producing only five million sperm (per milliliter), that is still good for fertilization so long as the quality is fine,” says Dr. Gagnon, who is also the director of the urology-research laboratory at the Royal Victoria Hospital in Montreal.
Then, too, individuals experience a huge swing in sperm output. Endocrinologist Alvin Paulsen, of the University of Washington in Seattle, charted the output of one fertile male over a 120-week period and found that sperm production swung from a low of two million per milliliter to a high of 170 million.
The Possible Effects of Climate Change on Fertility
Dr. Bruce Dunphy, a reproductive endocrinologist at the Foothills Hospital and the University of Calgary, notes that sperm production also appears to go through seasonal variation – dropping particularly in summer months. “It could be that increased exposure to ultraviolet radiation, or sun light, cuts sperm count. And if ultraviolet radiation is increasing, then that could account for the drop in sperm concentration in the population.”
Certain substances, including lead, cadmium, manganese, mercury and various pesticides, have been shown to impede fertility in laboratory animals. And workers who have come into close and prolonged contact with these chemicals have also been shown to experience reproductive dysfunction, ranging from damaged sperm to no sperm at all.
Most people, of course, are exposed to much lower levels of these potentially harmful substances. Researchers admit they don’t have a clue about the long-term consequences of low levels of toxins.
Dr. Gagnon said he believes that men who are bordering on infertility could be pushed over the edge by pollution. “It is likely that this decrease in sperm quality will not affect the fertility status of men with excellent semen quality. However, men who had marginal fertility with low- normal to slightly abnormal sperm variables may be rendered infertile by such exposure to environmental toxins,” he wrote in a scientific paper.
He added that this slight tip in the fertility scales might not show up when these men are lumped into figures for the entire population. But for the men involved, it is a very real and troubling problem.