A study of Los Angeles has found that the risk of dying in parts of the traffic-clogged, polluted city are far higher than previously believed.

Research comparing the risks of living in richer, beachfront neighborhoods with the hazy and fast-growing inland areas found the risk of death rose by 11 to 17% from the cleanest parts of Los Angeles to the most polluted areas of Riverside and San Bernardino counties to the east. The risk of fatal heart disease rose by between 25% and 39%.

This is the first study to compare pollution within a city rather than comapring one city with another and it shows that pollution is a significant - rather than a minor - factor in death rates.

"It's what we can't see that is most dangerous to us," lead author Michael Jerrett of the University of Southern California's Keck School of Medicine told Reuters.

The study showed that the concentration of airborne particles - tiny specks of solids and droplets of acids and other chemicals - rises by almost 20 micrograms per cubic meter as commuters head east from LA’s wealthier, westside neighborhoods.

It is these smallest particles of pollution that pose the greatest health risk since they sink deep into the lungs and enter the blood, causing inflammation and a thickening of artery walls that can prompt heart attacks and strokes.

Los Angeles is notoriously polluted. It is circled by mountains that help trap pollution in a basin. The advantage, if you can use that word, is that this produces bigger, easier to see changes. It is fair to assume that other less easy to measure cities will be similarly affected.

"I think that's something we need to investigate further," Jerrett added.

The study, based on an analysis of data on almost 23,000 people tracked by the American Cancer Society, also found that the risk of death from diabetes almost doubled in the more polluted areas of Southern California.

Source: Male Health - www.malehealth.co.uk