Inhaling polluted air increases the risk of type 2 diabetes, the first study in India has found. Research conducted in Delhi and the southern city of Chennai found that inhaling air with high amounts of PM2.5 particles led to high blood sugar levels and increased type 2 diabetes incidence.
When inhaled, PM2.5 particles – which are 30 times thinner than a strand of hair – can enter the bloodstream and cause several respiratory and cardiovascular diseases.
The study is part of ongoing research into chronic diseases in India that began in 2010. It is the first to focus on the link between exposure to ambient PM2.5 and type 2 diabetes in India, one of the worst countries in the world for air pollution.
The average annual PM2.5 levels in Delhi was 82-100μg/m3 and in Chennai was 30-40μg/m3, according to the study, many times the WHO limits of 5μg/m3. India’s national air quality standards are 40μg/m3.
There is also a high burden of non-communicable diseases, including diabetes, hypertension, and heart disease in India; 11.4% of the population – 101 million people – are living with diabetes, and about 136 million are pre-diabetic, according to a paper published in the Lancet in June. The average diabetes prevalence in the European Union was 6.2% in 2019, and 8.6% in the UK in 2016.
The Lancet study found India’s diabetes prevalence to be higher than previous estimations and showed a higher number of diabetics in urban than rural India.
In the BMJ study, the researchers followed a cohort of 12,000 men and women in Delhi and Chennai from 2010 to 2017 and measured their blood sugar levels periodically. Using satellite data and air pollution exposure models, they determined the air pollution in the locality of each participant in that timeframe.
They found that one month of exposure to PM2.5 led to elevated levels of blood sugar and prolonged exposure of one year or more led to an increased risk of diabetes. They found for every 10μg/m3 increase in annual average PM2.5 level in the two cities, the risk for diabetes increased by 22%.
“Given the pathophysiology of Indians – low BMI with a high proportion of fat – we are more prone to diabetes than the Western population,” said Siddhartha Mandal, lead investigator of the study and a researcher at the Centre for Chronic Disease Control, Delhi.
The addition of air pollution – an environmental factor – with lifestyle changes in the past 20 to 30 years is fuelling the increasing burden of diabetes, he said.
“Until now, we had assumed that diet, obesity, and physical exercise were some of the factors explaining why urban Indians had a higher prevalence of diabetes than rural Indians,” said Dr V Mohan, chairman of the Madras Diabetes Research Foundation and one of the authors of the paper. “This study is an eye-opener because now we have found a new cause for diabetes which is pollution.”
A man has his blood sugar checked at a mobile clinic outside the Geeta Colony area of Delhi. Cases of diabetes and hypertension have been rising rapidly among slum dwellers in India.
Another study on the same cohort in Delhi found average annual exposure to PM2.5 in Delhi (92μg/m3) led to an increase in blood pressure levels and a higher likelihood of developing hypertension.
Together, the studies show that the higher than safe levels of PM2.5 in the air in Indian cities cause diabetes and hypertension that could lead to atherosclerosis (the build-up of fatty deposits in the arteries), heart attacks, and heart failures, said Mandal.
PM2.5 contains sulfates, nitrates, heavy metals, and black carbon that can damage the lining of blood vessels and increase blood pressure by stiffening the arteries. The particles can get deposited in the fat cells and cause inflammation and can also attack the heart muscle directly, said Dr Dorairaj Prabhakaran, cardiologist and executive director of the Centre for Chronic Disease Control and one of the paper’s authors.
Acting as an endocrine disruptor, PM2.5 hampers insulin production in the body and its effect.
In urban India, there has been a rise in hypothyroidism, polycystic ovarian syndrome (PCOS), and gestational diabetes. This study shows that pollution may play a part in causing all of these as it disrupts the endocrine system that produces all hormones in the body, said Mohan.
The researchers are now working to understand the impact of pollution on cholesterol and vitamin D levels in the body, and its impact on the life cycle of individuals, including birth weight, pregnant women’s health, insulin resistance in adolescents, and the risk for Parkinson’s and Alzheimer’s disease, among others.
While its findings are alarming, the study gives scientists hope that bringing down pollution can decrease the burden of diabetes, as well as other non-communicable diseases, said Prabhakaran.
Some public policy initiatives have shown results. Since a public outcry about air pollution in 2016, the central and Delhi governments have banned older diesel vehicles, limited construction, built highways that bypass the city, and banned the burning of crops. Reports suggest there was a 22% reduction in PM2.5 levels between 2016 and 2021.
“This is a modest but welcome reduction. Similar measures adapted to local conditions are urgently needed across the country,” said Prabhakaran.