14 DAY TRIAL // The weakness of the males is increasingly showing up.
A new research reveals that, in the past three decades, the number of male births has decreased yearly in the U.S. and Japan.
The University of Pittsburgh-led research found significantly fewer boys being born relative to girls and that a rising percentage of dead fetuses to be male translated to 135,000 fewer white males in the U.S. and 127,000 fewer males in Japan over the last 30 years.
"The pattern of decline in the ratio of male to female births remains largely unexplained," said Dr Devra Lee Davis, lead investigator of the study, director of the University of Pittsburgh Cancer Institute's Center for Environmental Oncology and professor of epidemiology, University of Pittsburgh Graduate School of Public Health.
"We know that men who work with some solvents, metals and pesticides father fewer baby 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 that some combination of these factors, along with older age of parents, may account for decreasing male births."
It is known that prenatal exposure to endocrine-disrupting contaminants may impact the SRY gene (located on the Y male chromosome that induces the male sex of a fertilized egg).
Other factors affecting the viability of a male fetus are the parents' weight, nutrition and alcohol and drugs intake.
The research signals an overall decrease of 17 males per 10,000 births in the U.S. and of 37 males per 10,000 births in Japan since 1970, even if fetal death rates have generally got down.
In Japan, the dead fetuses were made up of males in 66 % cases compared to slightly over 50% in 1970.
In the case of African-Americans, even if the number of male births has slightly risen, the ratio of male to female births in their case keeps on being lower than that of white people.
Moreover, African-Americans displayed a higher fetal mortality rate overall and a higher proportion of male fetuses that die. "These results are not surprising since the black-white ratio in terms of infant mortality has remained the same for almost 100 years," said Dr Lovell A. Jones, study co-investigator and professor and director, Center for Research on Minority Health, department of health disparities research, University of Texas M.D. Anderson Cancer Center.
"Given the higher mortality rates for African-American males in the United States, these results reemphasize the need to determine all factors, including environmental contaminants, which are responsible for this continuing health disparity."
"Given the importance of reproduction for the health of any species, the trends we observed in the U.S. and Japan merit concern," added Davis. "In light of our findings, more detailed studies should be carried out that examine sex ratio in smaller groups with defined exposures as a potential indicator of environmental contamination."