Longevity Briefs: Does Heavy Pollution Hasten Ageing?

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Ageing and type II diabetes are closely linked. The primary component of type II diabetes is a reduced response to the blood sugar-lowering hormone insulin and, consequently, elevated blood sugar levels. These changes both promote other age-related diseases, and research shows that even when diabetes is controlled through medication, diabetics are still more likely than non-diabetics to develop conditions like heart disease. That’s because insulin signalling regulates more than just blood sugar and appears to be closely intertwined with the ageing process.

Many studies suggest that people living in more polluted areas get more age-related diseases including diabetes. Given that over half the world’s population lives in cities, reducing pollution could have a major impact on human longevity. Unfortunately, proving that pollution causes age-related diseases is hard because other factors linked to where people live (such as wealth and education) also have a strong influence on health.

What did the researchers do: In this study, researchers used data from a large prospective cohort study in India, called the CARRS (Center for cArdiometabolic Risk Reduction in South Asia) Surveillance Study. This study followed 12,064 adults from two major cities, Chennai and Delhi, for 7 years or more. The study collected information on the participants’ risk factors for diabetes (including sociodemographic factors), as well as their diabetes status. Specifically, they measured their fasting blood sugar, as well as something called glycosylated haemoglobin (HbA1c). The latter is a measure of sustained elevated blood sugar over a long period.

The researchers also used satellite models to estimate the daily average exposure to fine particulate matter (PM2.5), which are tiny particles in the air that can penetrate deep into the lungs and bloodstream. PM2.5 exposure was calculated for each participant based on their household location and the duration of the study. The researchers then analysed the associations between PM2.5 exposure and blood sugar, HbA1c and incident diabetes, using statistical models that adjusted for potential confounders and covariates.

Key takeaway(s) from this research:

• For every 10 μg/m3 increase in monthly average PM2.5, fasting blood sugar increased by 0.40 mg/dL on average, and HbA1c increased by 0.021 units on average
• For every 10 μg/m3 increase in annual average PM2.5, the risk of diabetes increased by 22% on average
• Risk did not increase in a linear way with increasing PM2.5

Higher exposure to PM2.5 was associated with significantly higher blood sugar, HbA1c and diabetes risk. An increase in PM2.5 of 10 μg/m3 was, on average, associated with a 22% increase in risk of developing diabetes that year, with risk increasing slightly for longer durations of exposure. To put this into context, the average PM2.5 in Delhi is about 50μg/m3, while the average in London is about 10μg/m3. The World Health Organisation recommends that that annual average concentrations of PM2.5 should not exceed 5 µg/m3.

While 22% was the average increase in diabetes risk per 10μg/m3 step, the relationship was not so neat and tidy. In both cities, risk of diabetes actually appeared to decrease at the highest PM2.5 levels. This is not the first study to report that risk starts to decrease at the highest PM2.5 levels, and it’s not entirely clear why this happens. It seems likely that some confounding variables or biases are at play – for example, what if people in the most polluted areas avoid going outside? It’s also possible that very high exposure has a diminishing health impact, much like how one cigarette a day is much worse than none, but the difference between 30 and 31 is not particularly evident.

How can we apply this knowledge today:

Studies have already been conducted in the western world suggesting that pollution increases diabetes risk. This study provides some much-needed data for India, which is a special case in multiple ways. Not only are Indian cities among the most polluted in the world, but Indian people are also genetically predisposed to diabetes. However, pollution may still have a significant impact on longevity in relatively clean cities. People may overlook pollution as a modifiable lifestyle factor under the assumption that there’s nothing you can do about it besides moving to a less polluted area, which is not always feasible. However, there are actually a few things you can do to reduce or mitigate the impact of pollution on your health (though of course, we would ideally find ways to reduce the levels of pollution in our cities):

• Avoiding outdoor activities during peak pollution hours or days.
• Using commercial air purifiers to improve the indoor air quality.
• Eating a healthy diet that is rich in antioxidants to help counteract the oxidative stress caused by air pollution.
• Exercising regularly and maintaining a healthy weight to improve insulin sensitivity and reduce blood sugar.
• Wearing a mask that can filter out PM2.5 when entering the most polluted zones.