It’s no secret that the car engine and factory fumes we breathe in everyday are seriously harmful to our brains and bodies.

A wealth of scientific evidence shows that those of us living in cities, exposed to high levels of air pollution throughout our lifetime, have an increased risk of heart disease, stroke, cancer and even mental health problems.

In fact, Britons are 64 times more likely to die from pollution-related illnesses than people living in Sweden, where the air is cleaner.

But now, intriguing new research reveals that aside from making us sick, toxins are also to blame for making us fat.

Researchers from the University of California followed more than 2,300 American children from early childhood and discovered that, by the age of ten, youngsters exposed to the highest amount of traffic pollution were, on average, more than 2lb heavier than children breathing cleaner air.

Crucially, scans of childrens’ lungs showed heavier children, living in more polluted areas, had significantly more signs of physical lung damage.

Could it be that we are unknowingly piling on the pounds every day... simply by breathing?

Why does pollution make you fatter?

Scientists believe that breathing in irritant particles – from traffic fumes to cigarette smoke – triggers a cascade of inflammatory reactions in the body.

First, pollutants irritate the tiny air sacs in the lungs, setting off a stress response that involves the release of hormones. These reduce the body’s ability to absorb energy (or glucose) from food, leaving blood sugar levels uncontrolled.

When blood sugar levels are unstable, fluctuations in appetite increase, making us more likely to over-eat.

Pollutants also trigger the release of molecules called ‘cytokines’ which send the immune system into overdrive, causing inflammation in the brain and body.

Mice studies have shown that this brain inflammation can also lead to over-eating.

Trucks, buses and diesel cars are especially damaging due to the amount of nitrogen oxides they emit. Nitrogen oxides can develop into microscopic molecules known as particulate matter (PM) which further irritate the lungs.

These are coated in chemicals, so when you inhale them you’re carrying a collection of irritants deep into your lungs.

Once in your bloodstream, these trigger damage to the blood vessel walls, leading to heart disease and strokes.

Staying inside the car won’t protect you

You might think the greatest exposure to harmful fumes comes from being out and about in busy urban areas. But according to scientific studies, you’d be wildly mistaken.

I recently took to London’s Oxford Street – one of the UK’s most polluted streets – to test the hypothesis. Wearing a pollution-monitoring device, I walked for three miles down the bustling road and beyond, inhaling all the toxic fumes from cars, buses and vans alongside me. Then I walked back, but chose a different route, through the quieter back streets.

Finally, I jumped in a taxi and asked the driver to take me down the same three-mile route I had just walked.

So what happened? Unsurprisingly, the biggest spike in inhaled pollution, as detected by the monitor, occurred when I walked alongside roaring traffic.

In quieter back streets, levels dropped dramatically.

But the highest levels I encountered all day were, in fact, inside the taxi. Despite the windows being closed, a giant pool of invisible pollution had somehow made it into my taxi. And it’s not just exclusive to London.

Another of my experiments involved a Lancashire couple, Emma and Mark.

We asked them to wear air pollution monitors for a few days while going about their daily business. Mark got a lift to work and returned on foot, while Emma took the children to school by car.

Mark was inhaling twice as much pollution in the car on the way to work as he was on his evening walk home, and Emma’s air pollution recordings shot up simply by sitting in her hatchback.

A series of Dutch studies showed a similar phenomenon. Drivers inside vehicles were exposed to far higher levels of air pollution than those walking or cycling through the same urban routes.

The fumes enter the car via the exhaust, before being circulated by the fan or air conditioning. If windows are closed, the toxic pollutants are then unable to escape.

The solution is in an APP… and birch trees

The first and most obvious solution is to avoid driving in traffic and, where possible, walk or cycle down quieter roads.

Otherwise, a collection of helpful apps can track the air quality, helping you to locate areas of clean air that are local to you.

If you live in London or the South East, try London Air – both a downloadable app and website, or CleanSpace which uses nationwide data to map air pollution in real time.

And if you’re moving house, choose a street with plenty of trees.

A few years ago, as part of an experiment with Lancaster University, researchers and I planted silver birch trees in front of a row of four houses in a busy street, and monitored the pollution inside the houses.

We compared these houses with four others slightly further down the street with no trees outside.

A fortnight later we found the people in the houses with the birch trees in front had been exposed to half the amount of pollution than those in the houses without.

Why? Birch trees are covered with tiny hairs and ridges which trap small polluting particles.

Why not try a spot of gardening and see if you notice a difference? And if you find your jeans fit better, do write in and tell me.

Daily Mail