The study, which tracked the lives of 32,000 non-smoking women over 10 years, appears to go much further than any previously published in establishing a dramatic causal link between coronary ailments and passive smoking. In the same week that the British government pledged to ban tobacco advertising and sports sponsorship, the report is almost certain to harden attitudes of industrialised governments towards the tobacco industry.
It could also radically improve the chances of legal challenges pending in the United States to the cigarette manufacturers, where exposure to second-hand smoke is a central issue. For the cigarette giants, which include British American Tobacco, the findings could not have come at a worse moment.
Published in the American medical journal, Circulation, the report said that women who were regularly exposed to second-hand smoke at home or at work were 91 per cent more likely to have a heart attack than those who were not. Women who were only occasionally exposed to second-hand smoke faced a 58 per cent great risk of an attack. The implication is that "there may be up to 50,000 Americans dying of heart attacks from passive smoke each year," commented one of the report's authors, Dr Ichiro Kawachi, a professor at the Harvard School of Public Health. He added that he was "becoming more and more convinced of the causal association", between passive smoke and heart disease.
By contrast, the report suggests that the risk posed by passive smoke for the development of lung cancer is much less significant. Annually, Americans dying from cancer because of second-hand smoke may be only 3,000 to 4,000.
The study is so significant, because until now earlier studies had only shown a 20-30 per cent increase in risk from heart disease. This allowed sceptics to challenge the notion that passive smoking was dangerous.
The women, aged 36 to 61 were selected from a group of hospital nurses first identified in 1976. In 1982, the researchers began tracking 32,000 of the nurses, all of whom said they were non-smokers, had no prior history of heart or cancer problems and who were all exposed regularly to passive smoke.
Exposure to second-hand smoke is believed to have various physiological effects, including lowering levels of certain beneficial cholesterols, reducing oxygen supply, damaging arteries and raising the risk of blood- clotting. On the egal front, the report may be especially important for a huge class-action suit that is due to go to trial in Florida next month.
The case, in which the defendant is Philip Morris, promises to bring together some 60,000 current and former flight attendants who are seeking damages for the alleged damage done to them to exposure to smoke in aeroplane cabins.