Smoking Adds to High Mortality in Men on Lower Social Rungs

TORONTO, July 14 -- Cigarettes take an exceptionally high toll on blue-collar men, according to investigators here and overseas.

They have twice the risk of dying prematurely compared with men of higher social and economic classes, and half the difference can be attributed to smoking, found an international team.

The study of overall death rates in four countries for men ages 35 to 69 used 1996 mortality data. As an indirect measure of smoking death rates, the researchers used lung cancer death rates, plus a few other groups of causes (chronic obstructive lung disease, other cancers, other respiratory diseases, for example), according to a report published online July 13 by The Lancet.

This previously described indirect method of assessing smoking has the advantage of not requiring any knowledge of current or past smoking patterns, said Prabhat Jha, M.D., at the University of Toronto here, and colleagues in England, Poland, and Australia.

The highest and lowest social strata were based on social class (professional versus unskilled manual) in England and Wales; neighborhood income (top versus bottom quintile) in urban Canada; and completed years of education (more than versus less than 12 years) in the U.S. and Poland.

For England and Wales, the mortality risk was 21% vs 43%; for the U.S., 20% vs 37%; for Canada 21% vs 34%; and for Poland 26% vs 50%. The four-country mean absolute difference was 19%.

Strikingly, more than half of this difference in male mortality in the lowest social group in each country involved smoking. For England and Wales, 4% vs 19%; for the U.S., 4% vs 15% for Canada 6% vs 13%; and for Poland 5% vs 22%. The four-country mean was 5% vs 17%, for a four-country absolute difference of 12%, Dr. Jha said.

There are many factors other than smoking that differ between various social strata in these four countries, perhaps involving both the causes and the diagnosis and treatment of some of the chronic diseases of middle age, the researchers wrote. As smoking interacts with other risk factors, generally increasing their effects, the hazards might also be expected to be greater in the lower social strata, they added.

"Our indirect methods are obviously crude," Dr. Jha said, "and the precise numbers presented in the paper's tables should not be taken to be precise. However, the major pattern in these populations is clear."

"In these populations, most, but not all, of the substantial social inequalities in adult male mortality during the 1990s were due to the effects of smoking," said epidemiologist Richard Peto, Ph.D., a co-author at the University of Oxford. "Widespread cessation of smoking could eventually halve the absolute differences between social strata in the risk of premature death."

"Higher taxes, warning labels, and other tobacco-control interventions have already been shown to help increase smoking cessation rates, with higher taxes being particularly effective at raising cessation rates among less educated or poorer groups," Dr. Jha concluded.

In commentary on Dr. Jha's study, Michael Marmot, Ph.D., of University College London wrote that the study confirms previous findings that smoking is an important contributor to socioeconomic differences in mortality. However, another study, he noted, found that lung cancer mortality rates in non-smokers probably differ between countries and educational groups, "thus violating the assumption that the American cohort data can simply be applied universally."

But even if smoking's contribution to excess disease in the socially disadvantaged might be less than a half, "it does not detract from the essential importance of the study," he wrote. "If smoking were eliminated, average health would improve and socioeconomic differences in adult mortality would be less although still substantial."