Air pollution has predisposed humans to a range of diseases and most of them may lead to an early death. Researchers from the Imperial College of London found that exposure to polluted air more than three decades ago still affects mortality risk at present.

"We were surprised to find pollution has effects on mortality that persist over three decades after exposure," lead author Dr. Anna Hansell said.

The 38-year-old study involved following 368,000 residents in Wales and England. The researchers estimated air pollution levels in 1971, 1981, 1991 and 2001. They analyzed recorded levels of sulphur dioxide and smoke particles in the air and studied the data between 2002 and 2009.

"Air pollution has well established impacts on health, especially on heart and lung disease," Dr. Hansell said.

"The novel aspects of our study are the very long follow-up time and the very detailed assessment of air pollution exposure, using air quality measurements going back to the 1970s," she added.

Sulphur dioxide and smoke particles are emitted when fossil fuels such as oil, coal, diesel and petrol are burned. Though the way of measuring air pollution changed throughout time, particulate matter 10 (PM10) measurements are still used today. These are particles in air that are less than 10 microns.

Air pollutants especially those which are very small, pose serious effects to health. A small size of particulate matter can be inhaled and can cause irritation to the lungs. The condition of people already suffering from diseases like chronic obstructive pulmonary disease (COPD) and bronchial asthma may be aggravated through inhalation of these particles. In the long run, constant exposure to polluted air contributes to the development of respiratory diseases such as lung cancer, cardiovascular problems and premature death.

Published in the online journal Thorax on Monday, the study sheds light in the possibility that exposure to air pollution has long-term effects on mortality. What's more alarming is that it can persist even after decades of being exposed in the past.

"Our study found more recent exposures were more important for mortality risk than historic exposures, but we need to do more work on how air pollution affects health over a person's entire lifetime," Dr. Hansell said.

Photo: Eric Schmuttenmaer | Flickr