Research suggests that choking air pollution means children are born smaller, and may be more vulnerable to health problems as a result.

Air pollution reduces the weight of newborn children, says a new study that compared births in Beijing with 2008, the year that the Chinese capital hosted the Summer Olympics and lowered smog levels through curbs on car use and industry.

A study released Tuesday in the US-based journal Environmental Health Perspectives found that women who were eight months pregnant during the August 2008 Olympics gave birth to children who were on average 23 grammes heavier than newborn infants during the same period in 2007 and 2009, when many of the anti-smog controls weren’t in place.

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“Although the average 23 gramme difference might seem small to some, the study suggests that there is a link between pollution and lower birth weight,” said David Rich, a scientist at the University of Rochester and the study’s lead author.

Rich said that further studies would be required to explain the biological process by which toxic air quality could impair the late development of unborn children.

Children who are born underweight can be more prone to serious illnesses, such as heart defects, and suggestions that low birth weight is linked with pollution would the latest in a series of studies cataloguing the health impacts of toxic air.

According to a widely-quoted report released in 2013, high levels of smog in northern Chinese cities may slash average life expectancy by five-an-half years compared with relatively unpolluted areas in southern provinces.

Besides the obvious impacts on the lungs, heavily-polluted air in Chinese cities increases the risk of cancer, depression, learning difficulties, and strokes, say other researchers.

The impact of toxic air on children in China’s biggest cities already resonates strongly after the release earlier this year of the highly-successful documentary ‘Under the Dome’, in which a former TV journalist catalogued the impact of smog on her young daughter.

Some private schools in Beijing have created real-life domes of their own, installing inflatable shelters fed by air purifiers so that the children of the country’s wealthy are protected from the choking air outside.

Some Chinese subsidiaries of international companies have acknowledged the difficulty in retaining expat staff concerned about the impact of air pollution on their families.

Although a recent study by Greenpeace suggests that air quality in Beijing improved marginally in the first quarter of 2015 compared with 2014, the capital’s air remains hazardous most of the time, and is regarded as chronic in scores of other cities that together are home to hundreds of millions.

Vehicle emissions, construction and particulates from power plants and factories are primarily to blame, but a major improvement and victory in China’s self-declared “war on pollution” will likely require an acceleration of shutdowns in heavy industry, a bigger share of renewable energy, and greater availability of cleaner fuels and low carbon transport.