US study finds lower sperm count in country than city
Date: 13-Nov-02
Country: USA
Author: Maggie Fox, Health and Science Correspondent
Men living in rural Missouri had lower sperm counts than men living in New York, Minneapolis and Los Angeles, the researchers said in a report released this week.
It joins a collection of studies that have shown conflicting results on whether a man's sperm count is affected by where he lives and the kind of things he is exposed to.
"What we found is that men from Columbia, Missouri, which is an agricultural community, have significantly lower sperm density and sperm motility (movement) related to the three urban centers we looked at," Dr. Shanna Swan, who led the study, said in a telephone interview.
Swan, an epidemiologist at the University of Missouri in Columbia, who has devoted her career to this issue, believes agricultural chemicals may be to blame.
"A lot of agricultural chemicals are used around here and are known to get into drinking water," she said.
Writing in the December issue of Environmental Health Perspectives, Swan and colleagues across the country said they studied 512 couples receiving prenatal care at clinics. They interviewed the men and took blood and semen samples.
Semen quality was equally high in Minneapolis and New York, and slightly lower in Los Angeles. Men from around Columbia, Missouri, had sperm counts and quality that were significantly lower than men from any of the three cities.
Now Swan's team is now looking for clues in the men's blood. The U.S. Centers for Disease Control and Prevention is analyzing the blood for chemicals to see if there are differences between the city and country dwellers.
STRESS COULD BE A FACTOR
The team will also examine hormone levels. Besides chemicals, stress is another factor that could affect sperm, Swan said. "In another study (looking at stress), the only thing related to semen quality was loss - the death of a close family member or divorce," she said.
"One hypothesis is that population density itself might be increasing semen quality. There are some indications that in some animal species that are crowded, the dominant males become more fertile."
But most compelling to Swan are data that show that certain chemicals can act as endocrine disruptors, changing the way hormones work in the body.
They include pesticides such as DDT and industrial chemicals like PCBs. Such "gender bending" chemicals are blamed for causing genital abnormalities in animals such as frogs and alligators.
Fears that humans could be suffering similar, albeit more subtle, effects emerged in 1992, when Niels Skakkebaek and colleagues at Copenhagen University reported that sperm counts were falling around the world.
Researchers found declining sperm counts in Denmark, Paris and Scotland, although studies in Finland, the French city of Toulouse and New York showed no decrease. One study found New Yorkers had especially high sperm counts.
Babies are still being born, but Swan said sperm count could be a marker for other biological changes.
The CDC has found a doubling in the number of cases of hypospadias, a birth defect in which the opening usually found at the end of the penis develops somewhere else on the organ.
And childhood cancer rates are rising by about 1 per cent a year in the United States.
Swan's team is carefully examining the children of the men in their study to see if they have a higher rate of such conditions.