Is your bad cholesterol rising due to pollution? Here’s what a new AIIMS study says

We need to assess long-term exposure to PM 2.5, says lead study investigator Dr Siddhartha Mandal.

We are trying to understand how pollution also impacts those with a low BMI. (Representative/ Getty Images)

If getting stuck in a traffic jam with poisonous fumes swirling around you has been a regular feature in your daily commute, it might have affected your health over the years. A new study, conducted by the Centre for Chronic Disease Control, Public Health Foundation of India (PHFI) and AIIMS, Delhi, has shown that long-term exposure to pollution can increase your bad cholesterol and triglycerides and decrease your good cholesterol levels.

Conducted in Delhi and Chennai, the study found that exposure to ambient PM2.5, or fine particulate matter of 2.5 microns or lesser in diameter, was associated with an increase in low density lipoprotein (LDL) cholesterol and triglycerides and a corresponding decrease in HDL cholesterol among 21,000 participants, who are being followed since 2010-2011. Researchers have found that exposure to diesel exhaust erodes the antioxidant, anti-inflammatory and protective properties of high-density lipoprotein (HDL) or the good cholesterol.

The study has been part of a large project called Geo Health that has been going on since 2016 and is a collaboration between the Centre for Chronic Disease Control and Harvard School of Public Health. It had already established the link between pollution and hypertension (2020) and diabetes (2023).
The key takeaway of the study, says lead investigator Dr Siddhartha Mandal, is that pollution impacts our cardiovascular system more significantly than thought. And that if we control pollution, a modifiable risk factor, we could improve our cardiovascular health.

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“Not only did we see a spike in LDL levels with pollution, we found a differential effect between cities,” he says. So far, diet and physical activity have been the twin pillars for a safe lipid profile. Now it turns out that reducing air pollution is just as important, according to Dr Mandal. Excerpts:

How does air pollution impact lipid levels?

It causes inflammation of blood vessels in our body and oxidative stress, which is an imbalance between two different types of molecules in your body, free radicals and antioxidants. Now excess free radicals damage your body’s cells and tissues, leading to severe diseases like cancer, heart, liver and kidney dysfunction.

When we breathe, PM 2.5 particles go into our bloodstream and are transported into all our organ systems, not just our lungs. This triggers inflammation across our organ systems while oxidative stress changes our tissues, often leading to fat deposition in the liver, calcification and hardening of arteries.

We are trying to understand how pollution also impacts those with a low BMI (body mass index). Indians are highly predisposed to diabetes. Our physiology is a bit unique. There is a hypothesis that PM 2.5 might be affecting us differently than the Western population.

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What were the major differences between the Delhi and Chennai cohorts?

Although Delhi had higher pollution levels than Chennai, the side effects of PM 2.5 were stronger in Chennai. One potential explanation is that the effects of harmful chemicals are steeper at lower levels of pollution. Everyone in Delhi is exposed to higher levels of air pollution. People inhaling 80 micrograms per meter cube of PM 2.5 are already under enough stress, so a saturation of an extra 10 micrograms per meter cube is not going to change external conditions a lot as there is a plateauing effect. But if the range of PM 2.5 goes up from 30-40 micrograms per meter cube to 90-100 micrograms per meter cube, the change is steeper from lower levels. Besides, if we had regions in Delhi where people were exposed to lower levels of pollution, then we would have had a better comparison between cities.

What is the significance of this study?

The study shows that the effects of pollution are not just short-term or confined to respiratory distress. This is long-term and can cause chronic diseases. If someone already has hypertension, over time the person could develop diabetes as well as other co-morbidities. Air pollution, therefore, is a ubiquitous risk factor.