Passive smoking is a real threat, and can increase the chances of heart disease, scientists have established in a major new study. They are calling for a ban on smoking in all public places and in homes where there are children.

People who are exposed to between one and 19 cigarettes a day increase their risk of heart disease by 1.23 times, and the risk rose to 1.31 times among those exposed to more than 20 cigarettes a day.

Although the increased risk is small, it is important, say the researchers from Tulane University School of Public Health in New Orleans. Heart disease is the major killer in the West, accounting for 25 per cent of all deaths in the US. At least 100,000 lives in the US alone could be saved just by stopping smoking.

The researchers reviewed 18 studies into passive smoking, and found that passive smokers had an overall risk of heart disease of 1.25 times, compared with those who were not exposed to passive smoking.

It has been estimated that up to 43 per cent of children are exposed to cigarette smoke in their homes, childcare facilities and schools.

"The only safe way to protect nonsmokers from exposure to cigarette smoke is to eliminate this health hazard from public places and workplaces, as well as from the home," they conclude (New Engl J Med, 1999; 340: 920-6).