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This photo from The Journal of Science shows human sperm.AFP/AFP / Getty Images

In the Danish city of Aarhus, a big university town by the sea, young men stream into the offices of Cryos International each day to fill a cup with their semen – so many that there's a 600-person waiting list. Guinness World Records lists it as the planet's largest sperm bank: It has 140,000 samples available, ships to more than 65 countries and helps to impregnate close to 2,000 women a year.

International headlines have compared it to the new Viking invasion: "How Danish Sperm is Conquering the World," said one; another, "the Viking Baby Boom." Yet beneath the big horns and bravado, there has been more fretting in Denmark over the future of manhood than in most places on Earth.

One reason they are such avid sperm donors is that their own country is in need: Danes have among the world's lower sperm counts. They also have one of the highest rates of assisted reproduction (more than 8 per cent of births), testicular cancer and male genital abnormalities.

If the sperm story in a tiny country like Denmark can appear to have two very different sides, it's no wonder that it has become an epic saga of confusion and conflict in the rest of the world.

It was Danish scientists who first reported in 1991 that sperm counts were in free fall around the globe. They announced counts had dropped by an alarming 50 per cent worldwide between 1938 and 1990 and predicted the trend would continue, painting a picture so bleak it suggested all men were on the road to sterility.

Many scientists hammered the study as flawed, but the news went off like a bomb in the news media, igniting debates over a long, worrisome list of possible causes, from estrogen exposure to toxic chemicals to long car trips and tight pants.

Yet 20 years later, despite everything riding on it – male sexual health and the very survival of the species – researchers are split over whether it's true.

"We don't even have consensus about what determines quality sperm – is it density, shape, total number? … Is it big head movement, or big tail movement? It's like comparing apples and bananas," says Ole Schou, founder of Cryos. "But everybody in the general population thinks there's something wrong with sperm."

"This area is a mess," says Keith Jarvi, head of urology at Mount Sinai Hospital in Toronto. "The only consensus is we really don't know."

Some experts think things are looking up; others still fear that society may face the kind of apocalyptic scenario depicted in Children of Men, the 1992 P.D. James novel and 2006 film about a chaotic, wartorn world of humans unable to procreate. (The novel was in fact inspired by reports of falling sperm counts.)

It's a long route from the day that pure curiosity drove a 17th-century Dutch scientist to peer down his homemade microscope at the fluid he had captured from a conjugal romp.

Anton Van Leeuwenhoek worried that his descriptions of the wee creatures he saw swimming vigorously might "disgust or scandalize the learned." But the Royal Society of London took a longer view and published his descriptions of spermatozoa, the "sperm animals" he saw, as well as his hunch that sperm had something to do with fertility – even though many people for the next hundred years thought they were parasites.

Only in the 19th century were sperm recognized as the cellular seeds of male fertility. And soon after, people started counting them as a measure of such – in frogs, roosters and, eventually, men. By the 1930s, studies had stacked up enough to define a normal range, which led to international comparisons. It was in October, 1991, at a World Health Organization meeting on environment and reproductive health that researchers at the University of Copenhagen shocked the world with theirs.

Tracking sperm counts of nearly 15,000 fertile men published in 61 studies over 50 years, researchers led by Niels Skakkebaek found sperm concentration in human semen had fallen worldwide by nearly half – a progression they depicted with a dark line sloping down through the decades.

"It looked like a scatter-gram," said Dolores Lamb, president-elect of the American Society for Reproductive Medicine. "If you followed the linear, downward trajectory that the researchers had drawn through it – it said all men would be infertile by around 2010 … if the line continued."

Along with a reduction in male fertility, they wrote that the falling counts coincided with a troubling rise in abnormalities of male genitalia – testicular cancer, undescended testicles and misplaced urethras. Together, it looked to them like a collection of new disorders striking males, one they would later call "testicular dysgenesis syndrome." And the speed of it suggested an environmental culprit.

Bottom of the animal kingdom

In the days before Viagra, when issues around male sexual health were still in the closet, these findings stoked anxieties: Man's fertility had been measured, and he was falling short.

Yet, said Dr. Lamb, a fertility expert at Baylor College of Medicine in Houston, "people had a field day with this graph. Some researchers did their own analysis and said it wasn't a downward trajectory, but a U-shape, that something catastrophic happened to sperm counts in the 1970s – maybe something to do with Saturday Night Fever – and that things were on the upswing."

Bernard Robaire, a professor of pharmacology and expert in male reproduction at McGill University in Montreal, calls it "the worst statistically analyzed study that I've seen."

Yet even Dr. Robaire feels that "it was a good thing because it got people talking about men's health."

And so began a flurry of studies to investigate if human sperm was truly headed for extinction.

For Richard Sharpe, the world's interest in testes could not have come sooner. An expert in male reproductive health at the University of Edinburgh, Dr. Sharpe is troubled by the health of human testes. For the size of them, he says, men don't produce nearly enough sperm, and most of what they do make is useless – only 5 to 15 per cent is viable. For other male animals – "dogs, cats, sheep, mice, rats, cows, rabbits" – the ratio is nine out of 10: "We're in League Division 7, and every other animal is in League 1."

At the time of the Danish report, he and Dr. Skakkebaek were leading proponents of the idea that overexposure to the female hormone estrogen had put male reproductive health in peril.

The hypothesis suggests that estrogens found in everyday foods such as milk and soy, along with synthetic estrogens in pollutants, were wreaking havoc with male reproductive systems. It seemed to jibe with reports at the time of testicular cancer rising more than two-fold, news of fish (and other wildlife) becoming feminized and vexing reports, one of them from Canada, that the number of male children being born was lagging behind the number of females.

But studies since have not borne out the estrogen threat and most scientists have largely abandoned the idea, Dr. Sharpe included. Neither has research revealed any one environmental contaminant to explain lower sperm counts in the general population. Dr. Sharpe still suspects a combinations of chemicals play a role, but studies have yet to identify them.

Instead, he says, he now feels that the best predictor of a man's reproductive health is what happened with his mother while he was still in her womb.

Geography is destiny

Researchers trying to confirm the falling-sperm-count story were finding different answers all over the map. Numbers looked higher in Finland than Hong Kong, Scotland and parts of Africa. Recent Finnish numbers have fallen, while Sweden's are stable. Counts look good in France, and bad in Thailand. The U.S. tally plots east over west, with sperm counts higher in New York and lower in California.

"There's a difference between countries, there's a difference between men living in different parts of countries. There is just so much variation," Dr. Jarvi says. But he says no one can explain if it reflects differences in geography, temperatures, environment or genetics.

What's more, with all the things that can foul up sperm counts, experts say most studies to date are unreliable, including the Danish report that raised the flag in the first place.

A healthy man makes about 80 million sperm a day, or 100 a second. But these numbers can change with age, and by season, and dwindle for any number of reasons – if a man gets too hot or has too little sleep, has a car accident or, of course, has sex – suddenly his count lands in the low range.

A good study should have men abstain from ejaculation for two to five days to collect an accurate sample – but it's difficult to know for sure. "The most striking thing missing from [nearly half the papers in the Danish report]was the duration of abstinence prior to the sample collected," says Vancouver's David Mortimer, past president of the Canadian Fertility and Andrology Society.

In his controversial book The Skeptical Environmentalist, Bjorn Lomborg, a former member of Greenpeace, argues that semen samples collected in the 1930s before the sexual revolution and the birth-control pill should not be compared with those gathered after it: Modern men are far more sexually active, which might also explain why sperm counts seem lower.

Besides, sperm counts are "one of the least useful measures of fertility," compared with how well a sperm swims and its shape, Dr. Mortimer says. The trouble is that picking individual sperm out of the crowd under a microscope is tricky.

"It's like looking down on a very busy street from the 11th floor on Bay Street – you see cars … but you don't know anything about their engines," says Sergey Moskovtsev of the Create Fertility Centre in Toronto.

Labs are also notorious for miscounting sperm. Four times a year, the American Association of Bioanalysis sends out batches of the same semen sample to 500 U.S. labs for proficiency testing, Dr. Lamb says. Most fail.

Dr. Mortimer cites a study in which two labs tested a sample from the same man and found that "at the one lab the fellow would be identified as infertile, at another he could be a sperm donor."

Still, he adds, "I would say there probably is a decline in sperm counts worldwide – but I would not stand up in a court of law and say so."

Nor can anyone at the moment, says McGill's Dr. Robaire, who also serves as editor-in-chief of the Biology of Reproduction Journal. "I've seen too much garbage, too many bad studies."

His own reading of the numbers is that counts clearly fell after the Second World War, stabilized and then picked up slightly. The big postwar dip coincides with women picking up smoking, he suspects, as animal studies show maternal smoking can reduce the number of stem cells in the developing male that make sperm. (Danish women had the highest smoking prevalence in Northern Europe after the war, studies find, peaking at about 40 per cent in pregnant women in the 1980s.)

In Canada, meanwhile there have been no national sperm-count studies at all. "No one's bothered to put it together," Dr. Mortimer says. "The drive has not been there."

Yet, as the experts like to say, testes are like those old canaries in a coal mine – they die first if there's trouble. "Semen is a reflection of overall health and well-being," Dr. Moskovtsev says.

Down for the count

Over time, the World Health Organization has dramatically lowered the bar for a normal sperm count, based on sperm concentrations among men who impregnated a woman in a one-year period of unprotected intercourse. The guidelines used to peg the low end of fertility at 60 million sperm per millilitre, Dr. Moskovtsev says. Then it fell to 40, then 20 and in the most recent edition, published last year, it sits at 15 million.

Some researchers worry that this is a move in the wrong direction. In a letter published last week in the journal Science, Dr. Sharpe wrote: "It is time to stop accepting low sperm count as normal and confront the possibility that the fertility of present and future generations is at risk."

He says the latest research shows that the proportion of men with high sperm counts is declining, while the number of men with low counts is rising. And it's not just sperm counts, he says, but testosterone levels too – that hallmark hormone of manhood.

"It's declined, independent of age, on both sides of the Atlantic," Dr. Sharpe says. This could be due to the increase in obesity, he says, since abdominal fat can lower testosterone levels, or to conditions when a male fetus develops in the womb – one of the few areas of consensus in sperm studies today.

A woman's diet, lifestyle and environmental exposures, particularly in the early months of her pregnancy as male sex organs are forming, can have a major impact on the man her baby boy will grow up to be.

This is good news, Dr. Sharpe says. "It suggests the low-sperm-count trend is preventable." And in his opinion the need is urgent. "Men who have low sperm counts also tend to have more abnormal sperm," and if they make few sperm to begin with, and they delay having children and fertility declines with age, "there's not a lot of room to manoeuvre," he says.

But Dr. Lamb doesn't see the urgency. "If it was something terribly dramatic already, you should see evidence of it in infertility rates – and the incidence of that has not increased," she says. "In most Western countries, it hovers around 15 to 17 per cent of couples of reproductive age."

The number of people seeking infertility treatments has risen, she adds, but that's a reflection of the fact that it has become more socially acceptable to do so, and that more treatments are available.

"It's still an important hypothesis that sperm counts are falling," she says. "But there's no strong data, rigorously controlled, to suggest that men are at huge risk right now of becoming sterile."

Meanwhile, one of the more rigorous studies under way has crashed into controversy. A few years after the Danish study appeared, Dr. Skakkebaek and his team began an ambitious project to track sperm counts not by looking back at dubious data, but by looking forward. They began following 5,000 18-year-olds bound for the military, taking detailed histories and sperm samples year after year.

This spring, they sent a confidential interim report to the National Board of Health, showing they had found no decline in sperm counts over the past 15 years. Without the researchers' prior knowledge or permission, the board posted the report on its public website and refused to take it down. Another research team then analyzed the data in the journal Epidemiology.

It was billed as optimistic news, though it still carried a note of caution, warning that "it may be too early for society to dismiss the concerns" depicted in Children of Men.

Dr. Skakkebaek and his team faulted the other researchers for drawing misleading conclusions from the raw and incomplete data, which they said should have run at least 20 years to be remotely comparable with the older study's 50-year range.

Yet Peter Saugmann-Jensen, an official with the Danish health board, said the agency felt compelled to publicize the interim finding, given the widespread anxiety, especially in Denmark, over sperm.

He told the journal Science in June that the board "had concerns about a negative stamp being put on a whole generation of men," pointing out a article that dubbed Danish men "Little Princes of Denmark."

Before the board released the research, an official visited the sperm bank in Aarhus. He wanted to know if Mr. Schou, who has operated Cryos since 1987, had noticed any decline in semen.

"We told him we hadn't seen any decline, and he was glad to hear it," Mr. Schou says. "We're not about to be a dying species here. We're doing quite well."

Carolyn Abraham is The Globe and Mail's medical reporter.

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