The nation's third leading preventable cause of death is passive cigarette smoke, killing nearly 53,000 non-smoking Americans each year, researchers said Thursday.

The link between passive smoking and the development of heart disease was reported by researchers at the University of California, San Francisco, in Circulation, a journal published by the American Heart Association."This is the first clear statement that passive smoking causes heart disease," said Dr. Stanton Glantz, author of the article and an associate member of the Cardiovascular Research Institute at the university.

Thomas Lauria, a spokesman for The Tobacco Institute in Washington, D.C., said the study lacks scientific credibility.

"We believe that the existing science shows that any long-term effect of passive smoke has not been proven," Lauria said.

Dr. William Parmley, the university's chief of cardiology, and Glantz said they reached their conclusions by reviewing 10 studies of smokers' non-smoking spouses.

They concluded that 37,000 people die annually from heart disease contracted from passive smoke, another 3,700 die from lung cancer and 12,000 die of other forms of cancer caused by passive smoke.

Glantz said passive smoke is the third leading cause of preventable death behind active smoking, which kills 400,000 people annually, and alcohol, which kills an estimated 100,000.