During the 2008 Olympics in Beijing, the Chinese government took drastic measures to significantly reduce the amount of air pollution for a seven-week period. The children born of women who were pregnant during this period were both heavier and presumably healthier than average. Researchers believe this correlation is not just coincidence but gives a glimpse to the harsh affects that air pollution has on our health even before we’re born.

In a study, now published in the journal Environmental Health Perspectives, a team of researchers have suggested that air pollution is hazardous to the health of a fetus, especially during the final weeks of pregnancy when the fetus experiences the most growth.

The study focused on babies born in Beijing, prior, during, and after the 2008 Olympics as the model for the effects of air pollution on a fetus. The Chinese capital has long battled serious air pollution and, as reported by the South China Morning Post, the city can often be covered in thick, gray smoke for weeks on end. Outdoor air pollution in China is about 25 times higher than what the U.S. government would deem as safe, and data from the 2010 Global Burden of Disease Study has linked this to around 1.2. premature deaths each year.

As reported by The Wall Street Journal, during the 2008 Olympics the Chinese government took measures like shutting down factories, restricting the amount of cars on the road, seeding clouds, shuttering construction sites, and even cracking down on pollution given off by street vendor carts, all in an effort to ensure clear blue skies for the games.

After over a dozen American and Chinese doctors examined the records of more than 83,000 births in Beijing, results revealed that children born during the 2008 Olympic game period were on average 23 grams heavier than those born during both the year before and the year after the games. Previous studies believe that air pollution can affect the development of a fetus's central nervous system, cardiovascular, and skeletal systems; however, this has not been confirmed.

Unfortunately, according to the researchers involved, these effects are most likely not restricted to Beijing, as similar pollution problems affect many other cities throughout the world. “This study shows that pollution controls — even short-term ones — can have positive public health benefits,” said Junfeng Zhang, a doctor with Duke Global Health Institute and a co-author of the study, as reported by the Wall Street Journal.

The problem with air pollution is that tiny hazardous chemicals emitted by factories, car emissions, and coal burning escape into the air and cause adverse effects on human health and the environment. Air pollution effects on human health range from minor respiratory irritation to chronic breathing problems, heart disease, and even lung cancer.

Outdoor air pollution in China is about 25 times higher than what the U.S. government would deem as safe, and data from the 2010 Global Burden of Disease Study have linked this to around 1.2. premature deaths each year.

Source: Rich DQ, Liu K, Zhang J, et al. Differences in Birth Weight Associated with the 2008 Beijing Olympic Air Pollution Reduction: Results from a Natural Experiment. Environmental Health Perspectives. 2015.