Air pollution caused one in seven new cases of diabetes in 2016, according to a US study, which found even low levels raised the chances of developing the chronic disease.
Diabetes has primarily been associated with lifestyle factors like diet and a sedentary lifestyle, but research by the Washington University School of Medicine in St Louis said pollution also plays a major role.
The study estimated that pollution contributed to 3.2 million new diabetes cases globally in 2016 or around 14% of all new diabetes cases globally that year.
"Our research shows a significant link between air pollution and diabetes globally," said Ziyad Al-Aly, the study's senior author.
Pollution is thought to reduce the body's insulin production, "preventing the body from converting blood glucose into energy that the body needs to maintain health," according to the research.
Al-Aly said the research, published in the Lancet Planetary Health, found an increased risk even with levels of air pollution currently considered safe by the US Environmental Protection Agency (EPA) and the World Health Organisation (WHO).
"This is important because many industry lobbying groups argue that current levels are too stringent and should be relaxed. Evidence shows that current levels are still not sufficiently safe and need to be tightened," he added.
Researchers working with scientists at the Veterans Affairs' Clinical Epidemiology Center, examined data from 1.7 million US veterans who did not have histories of diabetes and were followed for a median of 8.5 years.
Patient information from the veterans was compared to air quality information to examine the relationship between pollution and diabetes risk.
The scientists found the risk of developing diabetes "exhibited a strong link to air pollution".
They then devised a model to gauge diabetes risks over different pollution levels and used data from the annual worldwide Global Burden of Disease study, to estimate the prevalence of diabetes caused by bad air.
Diabetes affects more than 420 million people globally and is one of the world's fastest growing diseases.
