Smoking killed nearly 5 million people worldwide in 2000, with men more than three times as likely as women to go to an early grave, according to a study published on Wednesday in the journal Tobacco Control.

Globally, the leading cause of smoking-related deaths was cardiovascular disease, which killed more than 1 million people in the industrialised world and 670,000 in developing countries, the study’s authors found.

That was followed by lung cancer in industrialised nations and chronic obstructive airways disease, which includes illnesses such as bronchitis, in developing countries.

More than half of all deaths occurred in smokers between the ages of 30 and 69, said the researchers based at Harvard University and the University of Queensland.

The team used statistical analyses and studied population and mortality data in 14 regions of the world.

They attributed an increase in smoking around the world since 1975 to one in 10 deaths among all adults and almost one in five in men.

The number of smoking-related deaths was evenly split between rich and poor nations, while North America had the highest number of smoking deaths in the industrialised world, accounting for nearly 25 percent of total adult mortality.

“The health consequences of smoking will continue to grow unless effective interventions and policies that curb and reduce smoking among and prevent increases among in these countries are implemented,” the authors wrote.

In a separate study published in the journal on Wednesday, a faulty gene that slows the liver’s ability to rid the body of nicotine was linked to addiction in new, young smokers.

Researchers from McGill University in Canada identified the genetic profiles of 228 students, aged 12-13 years, who smoked but were not addicted.

The students were monitored for two years, during which time 67 of them developed a nicotine addiction.

Researchers found youths with inactive variants of the CYP2A6 gene were nearly three times more likely to become addicted to the drug.

Although those youths with the inactive variant smoked the least - a weekly average of 12 cigarettes compared with 29 in students with a normal gene - the researchers suggested slow clearance of nicotine in their bodies was likely to make it more intense, thus boosting their dependence.

SOURCE: Tobacco Control, December 2004.