'Higher levels of carbon monoxide were associated with higher risk of hospitalisation for cardiovascular heart disease.'

Bell and researchers from the Johns Hopkins Bloomberg School of Public Health and the University of Southern California's Keck School of Medicine based their findings on an analysis of hospital records for 9.3 million Medicare recipients and data on air pollution levels and weather gathered between 1999 and 2005.

Their analysis took into account the health effects of other traffic-related pollutants, including nitrogen dioxide, fine particles and elemental carbon, said a Yale release.

These findings were published in Circulation: Journal of the American Heart Association.