Could air pollution make you fat? After rice, fast food and a sedentary work culture, Chennai’s smoke-clogged air could be contributing to obesity, a US study shows.

The study published in American Journal of Epidemiology last week suggests exposure to PAHs (polycyclic aromatic hydrocarbons), the smelly gas produced when diesel burns, could be causing childhood obesity.

While PAHs form a large chunk of the city’s vehicular air pollution, the toxic compounds are also produced from burning wood, charcoal and cigarettes. In 2011, the PAH levels recorded from samples of Chennai’s air were alarmingly high at 325.7 to 790.8 ng/m3.

While the US study is ringing alarm bells considering that many trucks and buses run on diesel, the Indian scenario is scarier — every second vehicle on Chennai’s streets is diesel-powered.

Scientists from Columbia University, where the study was conducted from 1998 to 2006, advise reducing pollution, especially since PAHs get easily absorbed by soil and water.

“The conventional theory is that city dwellers are physically inactive and eat fatty foods, leading to obesity. However, we now have evidence that shows common air pollutants such as dioxins, POPs (persistant organic pollutants) and PAHs damage cells in the pancreas, making urban residents prone to becoming obese and diabetic,” explains diabetologist V. Mohan, director of Madras Diabetes Research Founda-tion that conducts studies among schoolchildren.

Even as Chennai’s schoolchildren are considered the unhealthiest in the country, experts believe inflammation is also closely linked to obesity and diabetes; and pollution is a common cause.

Diesel vehicles on rise in TN

With each passing day, diesel vehicles keep piling up on TN roads at a massive rate, thanks to government subsidy which has made the price of diesel cheaper than that of petrol, so as to help farming and public transport sectors.

Authorities estimate that share of diesel vehicle in overall passenger vehicles must have crossed 50 per cent in the state. And, the sale of diesel cars has increased by 40 per cent in the city.

“The penchant for diesel vehicles has gone up considerably since last year and the eagerness for buying petrol cars among new vehicle buyers has gone down drastically ever since the country started witnessing subsequent deregulation of petrol prices,” avers a manager of a leading automobile showroom in the city.

He added that they were selling around 200 petrol cars and 70 diesel cars a month early 2011 and now the sales of petrol cars have gone down to 70 per month. Sale of diesel cars has picked up by 40 per cent and 100 cars are being sold every month, he said.

According to transport department, registration of diesel vehicles has escalated in recent times owing to increasing petrol prices.

“Vehicle buyers in rural areas prefer only diesel vehicles due to fuel efficiency, whereas in cities, where the liking for petrol cars was high, the trend seems to have changed. Even, auto drivers prefer diesel autos,” said a senior transport official.

Of the total 4.13 lakh passenger vehicles (bus, vans, autos, mini bus) in the state registered till last month, diesel vehicles amounts for more than 50 per cent, transport officials say, though the department does not have statistics on diesel vehicles.

For instance, numbers of lorries has increased over 300 per cent in last two decades (88,735 to 2.95 lakh).

Barring two-wheelers and some cars, all other vehicles run on diesel and their emission rate is relatively higher than petrol operated vehicles, the official added.