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Do Stress or Pollutants Mean Fewer Baby Boys?

Posted By Prucia Buscell, Thursday, October 29, 2009
Updated: Thursday, February 17, 2011
Men aren't an endangered species yet, but scientists are puzzled by a decline in the number of boy babies born in recent decades.

The number of male births decreased every year in the US and Japan between 1970 and 2002, according to a study led by the University of Pittsburgh Cancer Institute. The researchers reported a decline of 17 male births for every 10,000 births in the U.S., and a decline of 37 male births for every 10,000 births in Japan. They also found that while fetal death rates have generally decreased, the portion of male fetuses that die is increasing.

"The pattern of decline in the ratio of male to female births remains largely unexplained," Devra Lee Davis, PhD, MPH, a professor of epidemiology and lead author of the study. said in an article in PittChronicle, the newspaper of the University of Pittsburgh. "We know that men who work with some solvents, metals and pesticides father fewer boys. We also know that nutritional factors, physical health and chemical exposures of pregnant women affect their ability to have children and the health of their offspring. We suspect some combination of these factors, along with the older age of parents, may account for decreasing male births."

Dr. Davis thinks something unusual is happening, and researchers in other countries have reported changes in birth sex ratios as well as a higher potential for reproductive abnormalities and cancers in men. A study by Shiva Dindyal published in the Internet Journal of Urology in 2004 discusses declining sperm counts in men world wide in recent decades. He examines possible environmental and life style factors as the cause.

The Telegraph in the U.K. reported October 23 on a Danish government study showing that toddlers are subjected to a vast number of chemicals, such as dioxins, PVC, flame retardants, and the pthalates used to soften plastics, in clothing, toys, food and skin care products. The story refers to some chemicals known to disrupt endocrines as "gender bending", and suggests exposure may contribute to adult male infertility, male genital abnormalities, and a proportional increase in the birth of baby girls. A Chicago Tribune story by Judith Graham reports dramatic declines male births on the Aamjiwnaang First Nation Reservation, where there are no longer enough boys for a hockey team though girls have several sports teams. Researchers found only 46 of the 132 babies born on or near the reservation in Ontario, Canada, between 1999 and 2003 were boys. While the reservation is bordered by petrochemical, polymer and chemical plants and mercury and PCBs contaminate the creek that runs through the land, Graham reports, no conclusive proof exists that pollution accounts for declining male births. The story also reports that the miscarriage rate on the reservation is 40 percent.

The study by Dr. Davis and colleagues found that in Japan, two thirds of the fetuses that die are male, a substantial increase from 1970, when males accounted for slightly more than half of fetal deaths. They say the declining rates over the more than three decades means 127,000 fewer men in Japan and 135,000 fewer white males in the U.S. They also reported that African Americans have a higher rate of fetal death,higher rates of male fetal death, and fewer male births. Davis has explained that environmental exposure to endocrine-disrupting pollutants may impact the gene on the Y chromosome that determines sex of a fertilized egg. From conception to grave, males are more vulnerable to illness and death, which may account for the expected 106 baby boys world wide for every 100 baby girls. Boys still outnumbers girls at birth, but their numerical edge is dropping.

Some researchers also suggest dire stress may decrease the viability of Y bearing sperm, reducing the likelihood that boy babies will be conceived. Ralph Catalano, professor of health policy and management at the University of California Berkeley School of Public Health found lower male births during a period of severe economic hardship in East Germany, and in New York after 9/11.

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