The study, which appears online in the Lancet's July 15 issue, looked at nearly 600,000 deaths in men aged 35 to 69 years in the U.K., Canada, U.S. and Poland.
"Across two continents, we find that smoking-related diseases account for well over half of the big difference in death rates between rich and poor," says study co-author Richard Peto, professor of medical statistics and epidemiology at the University of Oxford.
Researchers used an innovative, indirect method to estimate the contribution of smoking to mortality risk. The lung cancer deaths occurring in the different study groups were used as a guide to the respective proportions of deaths attributable to smoking in each group. Results were consistent across the five national populations studied.
Although mortality from smoking has recently started to decrease among men in Europe and North America, during the present decade smoking still accounts for about one-quarter of all male deaths in middle age. The study offers particular clarity to global and public health policy makers concerned with addressing the higher mortality rate among socially disadvantaged groups.
"These findings emphasize the importance of getting more smokers, especially in the lower socioeconomic bracket, to quit," says study co-author Professor Prabhat Jha of U of T's department of public health sciences, director of the Centre for Global Health Research at U of T and St. Michael's Hospital and Canada Research Chair in health and development.
"This means widespread cessation of smoking would do more than anything else to narrow the inequalities in health between rich and poor," says Jha.