November 15, 2005 – More girls are born in the most polluted neighborhoods of São Paulo, Brazil than in less polluted ones, study finds1 unveiled at a recent conference of the American Society of Reproductive Medicine.
According to lead researcher Jorge Hallak of the University of São Paulo, the proportion of X and Y chromosomes present in semen is altered in men exposed to air pollution. It is these chromosomes that determine the sex of the embryo.
The researchers divided the megalopolis of 17 million inhabitants that is São Paulo into low, medium and highly polluted areas, based on air quality analyzes. They then listed the births in each of the sectors over a three-year period. The conclusion: 48.3% of girls are born in the least polluted areas and 49.3% of girls in the most polluted areas. This 1% gap is small, but it is significant, according to Jorge Hallak. “This 1% is about 1,180 baby boys less than expected,” he explains.
To validate their results, the researchers exposed mice to the same conditions as humans. They recorded similar variations in female / male ratios at birth. In addition, there were fewer sperms in the semen of male mice.
We do not know precisely the pollutant that could have such an influence on the sex of embryos.
Note that other scientists argue that stresses such as wars, natural disasters and terrorist attacks promote the birth of girls. Pollution should be classified, according to them, among these major stresses.
The fact remains that there are even more baby boys born (51.4%) around the world for several decades, according to the authors of the study.
Guy Sabourin and Johanne Lauzon – PasseportSanté.net
According to Nature, Science-Press Agency.
1. Hallack J, et al. Increased levels of air pollution and a decrease in human and mice male / female ratio in the city of SToo Paulo, Brasil. This study has not yet been published.