Risk of type 2 diabetes linked to air pollution in Chennai, Delhi Premium

Two studies published in international journals have reported a worrying link between air pollution levels and the incidence of type 2 diabetes in Chennai and Delhi. The study is notable not because the findings are new – they aren’t unprecedented – but because they have found that the link, which has been indicated in Western countries and more recently in China as well, also holds in India. Indian cities have consistently dominated the tops of lists of places with the worst air for residents, with air quality frequently several times higher than the limits set by the World Health Organisation.

Two studies published in international journals have reported a worrying link between air pollution levels and the incidence of type 2 diabetes in Chennai and Delhi. The study is notable not because the findings are new – they aren’t unprecedented – but because they have found that the link, which has been indicated in Western countries and more recently in China as well, also holds in urban India.

Indian cities have consistently dominated the tops of lists of places with the worst air for residents, with air quality frequently several times higher than the limits set by the World Health Organisation.

The new studies are part of the Centre for cArdiometabolic Risk Reduction in South Asia (CARRS) Surveillance Study. Here, researchers roped in 6,722 adults in Chennai and 5,342 in Delhi and tracked their health through questionnaires and blood samples, with which they checked for fasting plasma glucose (FPG) and glycosylated haemoglobin (HbA1c), at specific intervals from 2010 to 2016.

The researchers also developed air pollution and exposure models using, among other things, satellite data and emissions inventories.

Based on their findings, the researchers reported that 10 μg/m3 differences “in annual average PM2.5” could be related to a 9-36% higher risk of developing type 2 diabetes. They have interpreted the long-term follow-up of study participants to mean that the link between type 2 diabetes and air pollution is “not due to intermittent episodes of high pollution levels” but “long-term exposure to ambient PM2.5”.

They also reported that for every 10 μg/m3 increase a month in PM2.5 levels, FPG increased by 0.21-0.58 mg/dL and HbA1c by 0.012-0.024 in Delhi, and FPG increased −0.36-1.39 mg/dL and HbA1c 0.01-0.06 in Chennai. Over six months, a 10 μg/m3  change in PM2.5 levels resulted in a rough doubling of both ranges in Delhi, but couldn’t be associated with a statistically significant result in Chennai.

The paper published in BMJ Open Diabetes Research & Care also said that “hypertensive participants … were more susceptible to developing type 2 diabetes against long-term exposure to PM 2.5 in Chennai,” whereas “younger participants were more susceptible to developing [the disease] in Delhi”.