The researchers analyzed data from the Comparative Risk Assessment project and World Health Organization databases to determine the level of risk factors in different world regions, and separately for men and women; they also considered how hazardous each risk factor may be. The analysis covered all high-income countries together, and separated low-income and middle-income countries into geographical regions: East Asia and Pacific, South Asia, Europe and Central Asia, Latin America and Caribbean, Middle East and North Africa, and Sub-Saharan Africa. The nine risk factors were overweight and obesity, low fruit and vegetable intake, physical inactivity, smoking, alcohol use, unsafe sex, urban air pollution, indoor smoke from household use of coal and contaminated injections in healthcare settings.
They found that more than one in every three of the seven million deaths from cancer worldwide was caused by these nine potentially modifiable risk factors (2.43 million), with alcohol and smoking playing large roles in all income levels and regions. Worldwide, the nine risk factors caused 1.6 million cancer deaths among men and 830,000 among women. Smoking alone is estimated to have caused 21 percent of deaths from cancer worldwide.
In high-income countries, these nine risks caused 760,000 cancer deaths; smoking, alcohol, and overweight and obesity were the most important causes of cancer in these nations.
In low- and middle-income regions the nine risks caused 1.67 million cancer deaths; and smoking, alcohol consumption and low fruit and vegetable intake were the leading risk factors for these deaths. Sexual transmission of human papillomavirus is the leading risk factor for cervical cancer in women in low- and middle-income countries, particularly in Sub-Saharan Africa and South Asia, where access to cervical screening is also limited.
Among low- and middle-income regions, Europe and Central Asia had the highest proportion of death from cancer from the nine risk factors studied; 39 percent of 825,000 cancer deaths in the low- and middle-income countries of Europe and Central Asia were caused by these risks. The effects were even larger among men; one half of cancer deaths among men in the low- and middle-income countries of Europe and Central Asia were caused by these nine risks.
Majid Ezzati, senior author of the study and assistant professor of international health at HSPH, commented, "These results clearly show that many globally important types of cancer are preventable by changes in lifestyle behaviors and environmental interventions." He continued, "To win the war against cancer, we must focus not just on advances in bio-medical technologies, but also on technologies and policies that change the behaviors and environments that cause those cancers."
The study, "Causes of cancer in the world: comparative risk assessment of nine behavioral and environmental risk factors," The Lancet, Vol. 366, November 19, 2005, was funded by the National Institute on Aging and by the Disease Control Priorities Project.