That is the conclusion of a three-year, population-based, case controlled study of 382 non-smokers living in seven areas in the state of New York, half of whom had been diagnosed with lung cancer. The organizers of the study, from Yale University School of Medicine, among others, took lifetime residential histories, including information about exposure to environmental tobacco smoke. They then measured exposure in terms of 'smoker years' - a factor determined by multiplying the number of years the non-smoker lived in each residence by the number of smokers in the household.

'Household exposure to 25 or more smoker-years during childhood and adolescence doubled the risk of lung cancer,' said the study - a level of exposure experienced by about 15 per cent of the study subjects. This would be the equivalent of a child of 13 living with two smoking parents. Exposure any less than that during childhood did not increase the risk of lung cancer, according to the study. It also found no increased risk with exposure to smokers in adulthood, including to a spouse who smoked. These findings correlate with another study, also in the New England Journal of Medicine, that passive exposure to smoking adversely affected the growth and respiratory illnesses of children with cystic fibrosis, a chronic lung disease. The study found an apparent relation between the level of exposure a child had to smoking and the severity of his disease.

The results were published ironically at a time when the British Department of Health has announced that it will oppose a total ban on tobacco advertising, which the European Commission is expected to propose in 1991. The department continues to believe that the best course of action is a voluntary agreement with the tobacco industry. In that decision, Britain seems increasingly weak-kneed. Thus far, 19 countries, including Canada and New Zealand, have a total ban on tobacco advertising, and France is expected to follow suit with the 12 other European countries by 1993. New Zealand has adopted what stands as one of the toughest pieces of legislation against smoking to date. The Smoke-Free Environments Act bans all tobacco advertising and guarantees Kiwis the right to breathe unpolluted air in public places, including work.