Farm chemicals may affect male fertility, MU researcher says
By LYNN FRANEY

Men living in agricultural mid-Missouri are markedly less fertile than men living in New York, Minneapolis and Los Angeles, researchers at the University of Missouri-Columbia have found.

The researchers suspect that runoff from farm chemicals may be to blame.

The results "are important to couples that are trying to conceive. If we can find out what specific exposures were related to this reduced semen quality, we might be able to prevent delays in conception in the future," said Shanna Swan, the MU professor who led the study.

Swan said she hopes the study prompts further inquiry into how agricultural chemicals negatively affect people's bodies.

The study, conducted between 1999 and 2001, found that, on average, fertile men in Columbia produced 58.7 million sperm per milliliter of semen, compared with 80.8 million for men in Los Angeles, 98.6 million for men in Minneapolis and 102.9 million for men in New York City.

On another important measure, sperm mobility, fertile men in Columbia also lagged behind their urban counterparts.

On average, fertile men in Columbia produced just 113 million mobile sperm per sample, compared with 162 million in New York, 196 million in Los Angeles and 201 million in Minneapolis. Swan measured mobile sperm by the sample, not by the milliliter, as was used to measure the number of all sperm.

The mobility measure is important because so few sperm make it to the woman's fallopian tubes. After sperm has been deposited in the vagina, only a small percentage find their way into the cervix and then begin their journey though the uterus and into the fallopian tubes. That journey must occur to fertilize the woman's egg. Only 1,000 or 2,000 sperm usually make it.

"While it's true that it only takes one sperm to conceive a pregnancy, the length of time that it takes a couple to conceive is related to the sperm quality -- how fast and directly the sperm swim, and how they are shaped," Swan said. "If you follow couples trying to become pregnant, those that have better semen quality do conceive more quickly."

Swan's research corroborates an earlier study that found lower sperm counts among men in Iowa City, Iowa, the only other semiagricultural region used in a U.S. semen-quality study.

That 1974 study found the sperm concentration of Iowa City men was 48 million per milliliter of semen.

The MU study will be published in today's edition of Environmental Health Perspectives, the scientific journal of the National Institute of Environmental Health Sciences. The unit of the National Institutes of Health provided Swan a $2.8 million grant to conduct the research.

Swan did not connect lower sperm counts and quality to particular agricultural chemicals. But the study does highlight the significant difference in land use among the other sites studied.

According to the U.S. Department of Agriculture, Swan wrote, about 57 percent of the land surrounding Boone County, where Columbia is located, was used for agriculture, compared with 19 percent in Minneapolis, 5 percent in Los Angeles and 0 percent in New York.

The study recruited 512 men whose pregnant partners were visiting hospitals for prenatal care in Columbia and the three other cities.

Researchers noted where the men had lived before moving to Boone County, if they were not Boone County natives. Swan said even very recent exposure to farm chemicals, not just long-term exposure, could affect one's health.

Swan, who has been a professor at the MU School of Medicine for four years, said she plans to publish a research article also based on the study's data that deals with specific agricultural chemicals.

Swan said she also would like to follow the children delivered by the women whose partners participated in the study to see whether where they were conceived -- an agricultural or urban area -- affected their future health.

"Semen quality doesn't get affected in a vacuum," Swan said. "We might call it the canary in the mine shaft. It indicates other potential reproductive problems because it relates to testicular function. There may also be problems in the woman's reproductive function. And there may be indications in other health areas, perhaps links to cancer down the line."