Air pollution linked to surging Type 2 diabetes cases, finds 7-yr study of Delhi & Chennai residents

New Delhi: Type 2 diabetes has now been added to the long list of diseases directly associated with air pollution, according to a critical first-of-its-kind study from India that was published in the British Medical Journal (BMJ) Thursday.

Conducted in Delhi and Chennai between 2010 and 2017 by researchers from India and the US, the study showed that inhaling air with high amounts of particulate matter (PM) 2.5 — one of the air pollutants associated with multiple health risks — led to high blood sugar levels and raised incidence of Type 2 diabetes.

PM2.5 are fine inhalable particles, with a diameter of 2.5 micrometres or smaller, are about 30 times thinner than a strand of human hair, and can easily enter the bloodstream.

The findings come at a time when major cities in India, mainly the Delhi-National Capital Region and Mumbai, are seeing thick layers of haze with air quality index (AQI) in some parts rising as high as over 600, indicating “hazardous” air quality. A high AQI in an area indicates a dangerously high level of PM2.5 particles, along with other pollutants.

Previous studies have shown that when inhaled, PM 2.5 particles can lead to respiratory and cardiovascular ailments. However, the latest study for the first time establishes a connection between air pollution and diabetes in India.

The study also follows one by Indian Council of Medical Research–India Diabetes (ICMR-INDIAB), published this June, that found that there were 101 million diabetics in India.

The latest findings, say researchers, now explain the high prevalence of diabetes in urban parts of the country.

“We have known for several years about the urban-rural differences in prevalence of diabetes and the urban prevalence of diabetes has always been known to be higher,” Dr V. Mohan, chairman and chief diabetologist at Dr Mohan’s Diabetes Specialities Centre (MDSC) in Chennai and an author of the study, told ThePrint.

“This has mostly been attributed to increased obesity, less physical activity and unhealthy diet with more carbohydrates, fats, calories, etc,” he added.

“Of course, all these are more common in urban areas. But now, this new study shows there could be yet another explanation for the higher prevalence of Type 2 diabetes in urban areas,” he said.

Also Read: 11% Indians diabetic, 36% have hypertension, says pan-India Lancet study on lifestyle diseases

Study details

In the BMJ study, researchers associated with Harvard University, Public Health Foundation of India, All India Institute of Medical Sciences, Delhi, and MDSC followed a cohort of 12,604 men and women in Delhi and Chennai from 2010 to 2017 and measured their blood sugar levels periodically.

According to the study paper, the average annual PM2.5 level was 82-100μg/m3 in Delhi and 30-40μg/m3 in Chennai in the seven-year period, while the World Health Organization’s prescribed limit for this is 5μg/m3.

India’s national air quality standards put the permissible level for PM2.5 at 40μg/m3.

Using satellite data and air pollution exposure models, the researchers determined the air pollution in the locality of each participant during that time period.

They found a link between rising PM2.5 levels and rising fasting plasma glucose levels and glycosylated haemoglobin (HbA1c) levels — the two markers of diabetes.

“…our results suggest a link between long-term exposure to ambient PM2.5 and Type 2 diabetes, which may have potential public health significance as well as policy implications for India, a country with high levels of ambient pollution as well as high burden of cardiovascular and cardiometabolic diseases,” the authors write.

In Bangladesh, India, Nepal and Pakistan, residents are expected to lose about five years of life expectancy on average if levels of pollution persist, according to the Air Quality Life Index report for the year 2023 by the Energy Policy Institute at University of Chicago.

PM2.5 disrupting metabolism 

Mohan explained that while it is known that PM2.5 can produce respiratory diseases, including chronic obstructive lung disease, asthma, emphysema and probably even lung cancer, there is now new evidence that it can also act as an endocrine disruptor.

“In the case of diabetes, it can lead to, number one, reduced insulin secretion from the pancreatic beta cells. Number two, it can also produce insulin resistance both in the liver and in the muscles,” he said.

The researcher said that reduced insulin secretion and increased insulin resistance are the two primary pathophysiological defects in Type 2 diabetes.

“Now, with both of these getting affected due to the endocrine disruptor effect of PM2.5, it is not a surprise, therefore, that Type 2 diabetes is being linked to air pollution,” he added.

Commenting on the findings, Dr Rajeev Gupta, director of internal medicine at CK Birla Hospital in Delhi, who is not directly associated with the analysis, said that exposure to air pollution, particularly ozone and particulate matter, can also increase oxidative stress and low-grade inflammation in the body.

“This can lead to stress on the beta cells of the pancreas, which produce insulin. As a result, insulin production may decrease and insulin resistance may increase, leading to hyperglycemia and diabetes. Therefore, it is important to reduce the burden of oxidative and inflammatory stress by reducing environmental pollution,” he told ThePrint.

Implications for future policy 

Mohan said that while the study’s results are worrisome, there may also be a sign of hope because it tells us that by controlling pollution, at least to some extent, the rising diabetes epidemic in India can be slowed down or arrested.

Till now, said the diabetologist, we have blamed individuals for the increasing incidence of diabetes by saying the condition is largely lifestyle-related, but the findings show that curbing the epidemic of diabetes also depends on government and non-government entities.

In the paper, the authors write: “The combined evidence provides directions for devising and implementing region-specific and population-specific policies targeted towards reducing ambient air pollution to counter the high burden of diabetes in order to achieve significant population-level public health gains.”

(Edited by Nida Fatima Siddiqui)

Also Read: ‘Diabetes capital’ India slated to get world’s 1st once-a-week insulin ‘by 2025’