Declining Male Birth Rate Baffles Scientists

By | June 4, 2008

Declining Male Birth Rate Baffles Scientists

Once there was a kids’ hockey team on the reservation of the Aamjiwnaang First Nation in Canada just across the border from Michigan.

No longer. There aren’t enough boys.

This community, surrounded by dozens of pollution-spewing chemical plants, is an especially extreme example of a puzzling phenomenon playing out across the world, in countries as diverse as the United States, Sweden and Japan.

Though more boys are being born than girls in most places, their numbers are falling. And no one is sure why.

The change is small, but real. In the U.S., the number of baby boys vs. girls has been declining since 1970, translating into 17 fewer males for every 10,000 births or an estimated 135,000 fewer boys born between 1970 and 2002, according to a study last year in Environmental Health Perspectives.

Some experts suggest the shift is part of a naturally occurring, cyclical pattern in population dynamics. But others think a notable change is under way, driven by factors such as environmental contaminants and various types of stress, such as economic hardship.

These issues could affect boys more because they’re actually the weaker sex _ more vulnerable than girls to illness and death from conception to grave.

Nature’s way of compensating is to produce more males than females, increasing the likelihood that the sexes will survive to reproductive age in equal numbers. But recent decades have eroded the gap between the sexes.

The difference may seem tiny, but “it’s important to look at the really big picture here, which is that there are global indications that something unusual is going on,” said Devra Davis, director of the Center for Environmental Oncology at the University of Pittsburgh and lead author of last year’s report.

The sex ratio is an indicator of population health, and unexpected changes could be an important signal that people are at risk biologically, she said.

Several Latin American nations have reported a similar shift in the sex ratio at birth, as have Finland, Norway, Wales and the Netherlands. Late last year, several Arctic communities documented a startling decline in the number of boys being born. Studies have shown changing sex ratios in Italian cities and among fish-eating women in the Great Lakes region.

None of these countries or areas has a tradition of sex selection, which in any case usually favors boys.

The puzzling phenomenon has inspired a flurry of research on what could be causing the population shifts. Davis’ hypothesis is that “there is something happening after conception that is making it harder for boys to exist in the maternal fetal environment.”

A growing body of research indicates that could include exposure to pollutants such as pesticides, mercury, lead and dioxin. More controversial is the idea that synthetic chemicals known as endocrine-disrupters may be damaging male fetuses during critical periods of development or affecting men’s sperm counts and testosterone levels.

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That thesis is “very interesting and provocative” but hasn’t been proved, said Dr. Rebecca Sokol, past president of the Society of Male Reproduction and Urology.

The steepest sex ratio declines observed in the world have occurred on the 3,000-acre Aamjiwnaang (AH-jih-nahng) First Nation reservation in Canada.

The number of boys vs. girls there began dropping in the early 1990s, according to data published in 2005 in Environmental Health Perspectives. Between 1999 and 2003, researchers found, only 46 boys were born out of 132 recorded births.

“You get angry and you get worried, thinking what could be causing this,” said Ada Lockridge, a member of the tribe who compiled the data and has since become an activist. “And then you want to learn more.”

Dozens of petrochemical, polymer and chemical plants surround the reservation on three sides. Mercury and PCBs contaminate the creek that runs through the land, and air-quality studies show the highest toxic releases in all of Canada, said Jim Brophy, executive director of Occupational Health Clinics for Ontario Workers, based in Sarnia, the nearest city.

Several months ago, Brophy and co-worker Margaret Keith did additional calculations, finding that boys made up only 42 percent of the 171 babies born from 2001 to 2005 to Aamjiwnaang living on the reserve or nearby.

“A disruption in the sex ratio of this magnitude has to be taken seriously,” Brophy said. –RO

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