With air pollution being linked to Type 2 diabetes, India's battle intensifies

Research conducted in the national capital of Delhi and in Chennai has found that increased exposure to pollution increases the risk of Type 2 diabetes.

The association between long-term exposure to polluted air with particulate matter (PM 2.5) and high blood sugar and increased incidence of Type 2 diabetes were known. However, this particular study is the first to assess the impact in Indian metros.

The study, which was conducted among 12,064 participants in an adult cohort from urban Chennai and Delhi from 2010 onwards, revealed that when PM 2.5 particles — which are 30 times thinner than a strand of hair — enter the bloodstream, they can cause several respiratory and cardiovascular diseases.

The study, which is a part of an ongoing research into chronic diseases in India, is the first to focus on the link between exposure to ambient PM 2.5 and Type 2 diabetes in the country. Evidence from India linking air pollution with glycemic markers and diabetes has been limited until now, the study authors have stated.

The study population was 50 per cent female with a median age of 44 years in Delhi, while in Chennai it was 56 per cent female with a median age of 40 years.

In Chennai, the average annual PM 2.5 levels were 40.2 μg/ m3 (37.5–42.7) and 101.5 μg/ m3 (92.2–119.8) in Delhi. Concentrations in Chennai were four times the WHO recommended guidelines at that time and equal to the Indian National Ambient Air Quality Standards (40 μg/ m3) for annual average PM. Concentrations in Delhi, on the other hand, exceeded WHO and Indian standards by 10 times and 2.5 times respectively.

A recent cohort study in Taiwan had also reported a 1.28 times risk of incident diabetes in the second quartile of exposure (for mean PM 2.5), which is close to the findings in the combined study population in India across both cities—but at a lower concentration.

At a population level, reducing the monthly average exposures to the first quartile from the third quartile in each city would potentially reduce the prevalence of diabetes by 1–2 per cent. The study observed increased risk for developing diabetes in both cities with long-term exposure to PM 2.5, though it varied.

A 23 per cent increased risk of developing Type 2 diabetes was noted for a 10 μg/m3 change in long-term exposure to PM 2.5, which is higher than the reported risks from developed countries and indicates the relevance of reducing PM 2.5 exposures across the country to reduce the burden of diabetes and related diseases in a nation that is already the world's diabetes capital.

The longitudinal nature of the study along with the seven years of follow up suggests that the findings reported are not due to intermittent episodes of high pollution, thereby improving on findings from cross-sectional studies. The results instead suggest a link between long-term exposure to ambient PM 2.5 and Type 2 diabetes.

Doctors from the Centre for Chronic Disease Control, the Public Health Foundation of India, the All-India Institute of Medical Sciences, the Madras Diabetes Research Foundation, the Harvard T.H. Chan School of Public Health and the Rollins School of Public Health, Emory University, were part of the study.