LOS ANGELES: Inhaling polluted air for even two hours could raise the risk of heart disease, a new study finds, reports China's Xinhua news agency on Monday.

Those exposed to smog have even greater risk of cardiovascular disease, according to the study appearing in the September issue of Hypertension.

In the study, researchers at the University of Michigan tested 83 people as they breathed levels of air pollution similar to those in an urban city near a roadway.

The researchers looked at the participants' blood vessels and then their responses before and after breathing high levels of air pollution.

The results showed that microscopic particles in the air, rather than ozone gases, caused the rise in blood pressure and impaired blood vessel function.

The air pollution caused diastolic pressure the lower number in a blood pressure reading to rise within two hours.

Blood vessels were impaired for as long as 24 hours.

Although the increase may not mean much for healthy people, "this small increase may actually be able to a trigger a heart attack or stroke," said study author Dr. Robert D. Brook, an assistant professor of medicine, Xinhua said.

"If air pollution levels are forecasted to be high, those with heart disease, diabetes or lung disease should avoid unnecessary outdoor activity," Brook said. - Bernama