In 2012, about half a million of cases of cancer around the world were attributed to excess body weight, which extrapolates to 3.6% of all new adult patients.
The weight-related cancer burden was highest in developed countries; 63.8% of these obesity-related cancers occurred in North America and Europe.
The figures come from the International Agency for Research on Cancer (IACR), and were published online November 25 in the Lancet Oncology.
The IACR team, led by Melinda Arnold, PhD, points out that approximately one-quarter of these weight-related cancers — or 118,000 cases — could have been avoided if the mean body mass index (BMI) of the global population had remained the same as it was in 1982.
They note that the global prevalence of excess body weight in adults has increased by 27.5% during the past 3 decades.
"Our findings add support for a global effort to address the rising trends in obesity," Dr Arnold said in a statement. "The global prevalence of obesity in adults has doubled since 1980. If this trend continues, it will certainly boost the future burden of cancer, particularly in South America and North Africa, where the largest increases in the rate of obesity have been seen over the last 30 years."
However, an accompanying comment appears to disagree with this sentiment. This study provides an "important new context and baseline for understanding the global burden of cancer incidence in relation to high BMI," writes Benjamin Cairns, PhD, from the University of Oxford in the United Kingdom. He adds that "there are important differences between regions and countries," but points out that "the overall burden is fairly small."
"Arguably these findings do not give much additional support for a global effort to address rising obesity," Dr Cairns says. "Such an effort is certainly needed, but mainly because of metabolic and vascular diseases, which dominate the burden of ill health associated with obesity."
Dr Cairns notes that if 3.6% of cancer cases are associated with high BMI, which means nearly half a million cases, "this number is large mainly because the world population is large."
Resources for global cancer prevention are somewhat limited and, thus, "resources targeted at obesity need to be balanced against the other important causes of cancer, particularly infections and tobacco use, which are each associated with much larger proportions of cases," he concludes.
Model to Estimate Fraction of Cancers
The IACR team created a model to estimate the fraction of cancers that were associated with excess body weight in 2012. The population attributable fraction is used to estimate the proportion of cases that can be attributed to one or more specified risk factors. In this study, BMI estimates from 2002 and data from GLOBOCAN2012 were used to calculate the fraction of new cancer cases attributable to high BMI.
The team also calculated the proportion of cancers that were potentially avoidable had populations maintained their 1982 mean BMI.
The findings reveal that obesity-related cancer is a greater problem for women than men, largely because of endometrial and postmenopausal breast cancers. In men, excess weight was responsible for 1.9% (136,000) of the new cancers in 2012, and in women it was responsible for 5.4% (345,000) of new cases.
Overall, colon cancer in men and postmenopausal breast cancer in women were the most common cancers attributed to excess body weight.
For men, colon and kidney cancers accounted for more than two-thirds of all obesity-related cancers (nearly 90,000 cases). In women, postmenopausal breast, endometrial, and colon cancers were responsible for almost three-quarters of obesity-related cancers (almost 250,000 cases).
There were more cancers associated with excess body weight in developed countries than in developing countries in women (8.0% vs 1.5%) and in men (3.0% vs 0.3%).
North America contributed by far the most cases of cancer (111,000; 23.0%), and sub-Saharan Africa contributed the least (7300; 1.5%). In Europe, the burden was largest in Eastern Europe, which had more than one-third (66,000) of the total European cases associated with excess BMI.
The proportion of obesity-related cancers varied widely between countries, the researchers note. In men, it was particularly high in the Czech Republic (5.5% of the country's new cancer cases in 2012), Jordan (4.5%), Argentina (4.5%), the United Kingdom (4.4%), and Malta (4.4%). In women, it was strikingly high in Barbados (12.7%), the Czech Republic (12.0%), and Puerto Rico (11.6%). It was lowest in both sexes in countries in sub-Saharan Africa (less than 2% in men and less than 4% in women).
The study was supported by the World Cancer Research Fund International, European Commission (Marie Curie Intra-European Fellowship), Australian National Health and Medical Research Council, and US National Institutes of Health. The authors and Dr Cairns have disclosed no relevant financial relationships.
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Cite this: Obesity Linked to Half a Million Cancer Cases Worldwide - Medscape - Nov 25, 2014.