More than a third of cancer-related deaths worldwide can be associated with nine avoidable risk factors, a study by Harvard School of Public Health (HSPH) researchers has found.

In a report published in the UK medical journal The Lancet, the scientists attributed 2.43 million cancer deaths in 2001 to modifiable factors, such as obesity, low fruit and vegetable intake, lack of exercise, smoking, alcohol, unsafe sex, and urban air pollution.

HSPH Assistant Professor of International Health Majid Ezzati, the lead researcher of the study, said that smoking is the leading cause of death from cancer by some measures, making up 21 percent of all cancer-related deaths worldwide. He stressed that this ranking from the data reflected the widespread nature of smoking, however, rather than overall toxicity.

In terms of reducing cancer mortality in the near future, Ezzati said that the greatest potential lies in preventative medicine.

“Given what we know right now, prevention is the best way we have in our hands,” he said.

“Prevention of cancer is much more effective and cost-efficient because we have already made [progress] in treatment.”

He noted that this progress is less successful for cancers that have high mortality, such as liver and pancreatic cancer.

This study showed that in half of the high mortality cases, those cancers are preventable by modifiable factors.

Ezzati added that in the past century, reducing health risk factors has produced noticeable results.

“Historically, we have had success in reducing a lot of the risk factors,” he said. “There was a time when 60 percent of American men were smoking; now, it’s 25-30 percent. There’s no reason we can’t reduce it more. We have policy tools [available] to reduce pollution, and society should be thinking about [both] technology and policy intervention with health.”

The study discovered that certain factors were more prevalent in some areas, with smoking common around the world, but especially high in men living in east Asian countries. Obesity and lack of exercise, Ezzati said, were somewhat higher in high-income countries, such as the U.S. and European nations.

Dr. Goodarz Danaei, a HSPH graduate student who collaborated in the data analysis and writing of the report, described the data collection as a mass collaborative effort on the part of over 100 researchers worldwide belonging to a larger, ongoing project called the Comparative Risk Assessment group, with a core group of five HSPH researchers.

The analysts collected the independent studies of researchers focusing on a specific risk factor in a region, such as tobacco in South East Asia, he said. The researchers then calculated correlations between risk factors, the apparent harmfulness of those factors, and the prevalence of certain types of cancer in that region. The study also relied on data provided by the World Bank and the World Health Organization.