schoolsportHeightened levels of air pollution in major cities worldwide is leading to reproductive problems including low birth weight, miscarriage, preterm birth and decreased sperm quality, an international study has suggested.

Researchers from the University of Sao Paulo found there was a particularly marked effect on male births after dividing the city's districts into different categories based on their ambient particulate matter (PM10) concentrations over time.

PM10 levels as a marker of air pollution levels, the study found a direct correlation between increased pollution and less male births was found with more than 1% fewer males and more than 1% more females during the most polluted time periods from 2000-2007. The researchers estimated that there were nearly 31,000 less male births during the study period due to pollution.

Potential cause of social problems
Study lead Dr Simone Miraglia said: "Increasing differences in the male/female ratio at birth could lead, in a mid-to-long-term future, to a deficit in male population and probably cause social problems. This scenario gets worse if we consider that men are more prone to premature death because of their trend to engage in risk behaviour and violence.

"Although the biological mechanisms responsible for the male to female birth differentials are not clearly established, this study indicates that concentration of particulate air pollution in urban cities are associated with decreased male births. These findings further indicate why the abatement of air pollution is a target that governments must pursue."

The study also suggested that pollution had an effect on the health of eggs and sperm. Hormone levels within the mother and father are also effected by pollution and these changes may be reflected in a difference in the gender of the offspring.