Smoking is a global health hazard, causing nearly 5 million deaths worldwide in 2000, according to researchers.

Look past the staggering estimated death toll, and many questions arise: Were there any regional differences? What specific health problems were at work? Who was most vulnerable? And perhaps most importantly, where are the numbers headed?

Those are just a few of the questions addressed by researchers Majid Ezzati, PhD, of Harvard's School of Public Health, and Alan Lopez, PhD, of Australia's University of Queensland.

Ezzati first reported the estimated smoking death toll (search) about a year ago. Since then, he and Lopez have been combing through the world's death data, searching for clues about smoking deaths from Algeria to Zimbabwe.

Some of their findings may surprise you.

For instance, heart disease (search) — not lung cancer — was the leading cause of smoking deaths in industrialized countries. Heart disease accounted for about 43 percent of smoking-related deaths among men and women.

Lung cancer (search) accounted for only 22 percent of smoking-related deaths among men and 19 percent among women in industrialized regions. The results appear in the December issue of the journal Tobacco Control.

In developing regions, it was a different story.

Heart disease still held first place, accounting for 28 percent of smoking-related deaths. But lung diseases like emphysema were a close second, accounting for 27 percent. Lung cancer came in third, at just under 14 percent.

Ezzati tells WebMD that people in developing countries may be more vulnerable to lung conditions because they often rely on burning wood and coal to heat their homes and cook their food.

"What smoking really does is magnify existing risks," he says.

Likewise, poor diets combined with smoking may account for the large number of smoking-related heart disease deaths in Eastern Europe and the Indian subcontinent, says Ezzati.

Gender, Age and Smoking

More than half of all smoking-related deaths occurred in people aged 30-69.

There were 2.69 million smoking-related deaths in that age group, compared with 2.14 million in people aged 70 and older.

Most were men.

About 3.8 million men died from smoking, compared with 1 million women.

More men than women traditionally smoke, but Ezzati is concerned that women in developing countries, who traditionally haven't smoked in large numbers, may adopt this bad habit.

"The really important question is how much can female smoking be prevented or how high is it going to go?" says Ezzati.

Since lung cancer can take a long time to develop, deaths from lung cancer may yet rise in developing countries, where smoking is a newer habit.

"Some of the effects for developing countries are still going to appear in the next decade or two," says Ezzati.

"Arguably, smoking in Western Europe and North America has peaked. In North America, it's on its way down. In developing countries, it's just getting to peak among men," he says, noting that some countries, such as Thailand, have had success in antismoking efforts.

By Miranda Hitti, reviewed by Michael W. Smith, MD

SOURCES: Ezzati, M. Tobacco Control, December 2004; vol 13: pp 388-395. Majid Ezzati, PhD, Harvard School of Public Health. News release, BMJ Specialist Journals.