Results from Indian study add weight to the importance of reducing air pollution in urban areas globally, including the UK, to reduce negative impact on health
New research among residents of Delhi and Chennai has revealed that inhaling air highly polluted with PM2.5 particles is associated with elevated blood sugar levels and increased type 2 diabetes.
As part of ongoing research into chronic diseases in India, blood sugar levels of 12,000 participants were measured and correlated with air pollution in their respective localities; average annual PM2.5 levels were 82-100μg/m3 in Delhi and 30-40μg/m3 in Chennai, exceeding WHO recommendations of 5μg/m3.
Elevated blood sugar level was recorded amongst participants after a month of exposure, while exposure for over a year led to an increased risk of diabetes; for every 10μg/m3 increase in annual average PM2.5 level, diabetes risk increased by 22%.
"This study is one of the first in India to show the long-term effects of PM2.5 on incidence of type 2 diabetes within a locally recruited general population followed over time for seven years,” explained Siddhartha Mandal, lead investigator of the BMJ study and researcher at Delhi’s Centre for Chronic Disease Control. “The results show how exposure to PM2.5 affects glycaemic markers in short duration and increases the risk of developing diabetes in long-term in two cities with very different PM2.5 levels.”
Simon Heller, Professor of Clinical Diabetes, University of Sheffield said these results are “interesting and important,” and “indicate that the greater the amount of pollution the greater the increase in diabetes. This strongly suggests a causal link possibly through air pollution reducing the effectiveness of insulin which lowers glucose levels in the body.”
Around 101 million people (11.4%) in India live with diabetes; a further 136 million are considered pre-diabetic. In comparison, the average diabetes prevalence in the European Union was 6.2% in 2019, and 8.6% in the UK in 2016.
“There are major studies from India, USA and the UK, all of which demonstrate an association between [air pollution and type 2 diabetes].”
“Air pollution, particularly particulate air pollution and nitrogen dioxide, is increasingly being associated with type 2 diabetes,” said Professor Frank Kelly, School of Public Health, Imperial College London (ICL). “There are major studies from India, USA and the UK, all of which demonstrate an association between the two.”
India also has a high burden of non-communicable diseases and another study among the same cohort found average annual exposure to PM2.5 in Delhi led to an increase in blood pressure and higher likelihood of developing hypertension. These findings are “definitely a major public health concern” said Mandal, and several other cities likely experience similar effects.
Air pollution may also be a factor in hypothyroidism, polycystic ovarian syndrome and gestational diabetes as it disrupts the endocrine system. Researchers will now study pollution’s impact on cholesterol and vitamin D levels in the body, birth weight, pregnant women’s health, insulin resistance in adolescents, and the risk for Parkinson’s and Alzheimer’s disease.
Kelly says the next step is “to improve public understanding of the links between air pollution and poor health as well as regulatory policies that reduce major emissions from traffic, agriculture and construction sectors.”
Heller added, “The results add further weight to the importance of moves to reduce air pollution in urban areas globally, including the UK. This requires measures promoting cycling, walking and public transport as well as accelerating use of low emission vehicles."