Exposure to environmental tobacco smoke (passive smoking) is associated with a 15-35% excess risk of coronary heart disease and lung cancer. Environmental tobacco smoke may also be linked to stroke and other cancers, though evidence is scarce.
The rate of smoking in Chinese men is high, but most Chinese women do not smoke. This provides a good opportunity to evaluate this association in women.
Over 72,000 women took part in the study. They were aged between 40 and 70, had never smoked, and lived in seven areas of urban Shanghai, China.
Women were surveyed at the start of the study about smoking and other lifestyle factors, for themselves and for their husbands. Exposure was measured by the number of pack years (years of smoking multiplied by packs of 20 cigarettes) that the husband smoked during the marriage. Demographic details and disease history, reproductive history, family history, and dietary history were also recorded.
Two follow-up surveys were conducted during the course of the study to obtain information on death and common diseases diagnosed after the initial survey.
A high proportion of women (83.1%) were exposed to environmental tobacco smoke from their husbands, at work, or in early life (or in combination).
Exposure to tobacco smoke from husbands was associated with a moderately increased risk of death from all causes and more strongly with increased mortality due to cardiovascular disease and stroke.
Exposure in early life was also associated with increased mortality due to cardiovascular disease, while exposure to tobacco smoke at work was associated with increased mortality due to cancer, especially lung cancer.
These results are generally consistent with previous studies and suggest that exposure to environmental tobacco smoke at different times of life may contribute to the risk of different diseases, say the authors.
They also analysed the effect of duration of exposure to environmental tobacco smoke on mortality and found significant relations between deaths due to stroke and husband's number of pack years, between deaths due to lung cancer and total years of exposure at work, and between deaths due to cardiovascular diseases and total years of exposure in early life.
Given the high prevalence of exposure in this population, the impact of environmental tobacco smoke on all cause mortality could be substantial, they conclude.