THURSDAY, Nov. 17, 2005 (HealthDay News) -- One-third of the world's cancers are caused by nine modifiable risk factors, a new global survey found.
Tobacco leads the list, responsible for about 21 percent of all cancers, said Majid Ezzati, an assistant professor of international health at the Harvard School of Public Health.
"The second one is a combination of alcohol, and inadequate intake of fruits and vegetables," added Ezzati, lead author of the report that appears in Nov. 19 issue of The Lancet.
Others include overweight and obesity; physical inactivity; unsafe sex; urban air pollution; indoor smoke from household use of coal; and contaminated health-care injections.
As the final two entries on the list show, the risk factors for cancer that can be altered vary widely from country to country and culture to culture, Ezzati said. Indoor smoke from coal is not a great issue in the United States, but overweight and lack of exercise are important, he said.
"These are average numbers applied to large groups," Ezzati said. "For any individual, you would have to take a look at the individual setting. For example, if you live next to a truck depot that emits a lot of diesel exhaust, that would have a major affect on your risk."
Ezzati and his colleagues used data gathered in a Comparative Risk Assessment Project. The study was part of an overall Initiative for Global Health.
An estimated 2.43 million of the 7 million cancer deaths that occurred worldwide in 2001 were due to these nine factors, the researchers said. Of those deaths, 760,000 occurred in high-income countries, while 1.67 million took place in low- and middle-income regions.
The leading causes of cancer deaths in high-income countries such as the United States and Canada were smoking, alcohol and obesity. For low- and middle-income countries, the leading causes were smoking, alcohol and low intake of fruits and vegetables.
The estimates in the report are "cautious and conservative," said Dr. Graham A. Colditz, director of Harvard's Center for Cancer Prevention. Previous studies have estimated that up to 60 percent of worldwide cancers are due to modifiable factors, but the new report has a lower estimate because it was limited to instances where data were absolutely clear, he said.
For example, the new report doesn't include obesity as a risk factor for kidney cancer, which is included by the International Agency for Research on Cancer, Colditz said. "They [the study authors] are leaving out cancers that were clearly known as related to such risk factors," he said.
The report noted that prevention is important because "advances in cancer treatment have not been as effective as those for other chronic diseases."
That is basically accurate, said Ahmedin Jemal, program director for cancer occurrence at the American Cancer Society, although there have been broad advances in treatments against some cancers, such as leukemias.
But undeniably, "prevention is preferable to treatment," Jemal said. One of the great values of the study is that it shows that working to lower cancer rates through risk factors that can be modified by personal behavior "is a story not only for developed countries but also in developing countries," he said.
For Americans, the study emphasizes the need to follow recommendations about not smoking, avoiding excess weight and getting exercise, Jemal said.
To assess your risk for cancer and other diseases, visit the Harvard Cancer for Cancer Prevention.