Dr Melina Arnold is a Postdoctoral Fellow at the International Agency for Research on Cancer (IARC) the World Health Organization’s specialist organisation for cancer.
Dr Nirmala Pandeya is a Postdoctoral Fellow at the School of Population Health, Faculty of Medicine and Biomedical Sciences, University of Queensland, Australia.
The obesity epidemic is currently one of the most discussed health topics around the globe. Overweight and obesity have been increasing dramatically in the last few decades. In a 2012 study, Stevens et al estimated that 35% of the adult population is overweight and 12% obese - a doubling of prevalence since 1980.
Overweight and obesity are known risk factors for a number of cancers including: gullet (oesophageal adenocarcinoma), bowel, kidney, pancreas, gallbladder, ovary, womb, prostate and breast in women after menopause, as well as several other chronic diseases. Yet, a picture of the impact of overweight and obesity on cancer rates at the global level is still missing.
We, at International Agency for Research on Cancer (IARC), supported by World Cancer Research Fund International, have been working through a large international collaboration to try and fill in this gap. Several scientific studies across the world have tried to address this topic using varying methodologies. In our project, we attempted to assess the global burden of new cases of cancer (incidence) that could be considered as resulting from overweight and obesity - measured as excess in body mass index (BMI) - particularly in terms of the 10-year time period between onset of excess BMI and development of cancer.
We put together available information on excess BMI in the global population and the increased risk of cancer incidence due to excess BMI, to arrive at an estimate of cancers that could be attributable to overweight and obesity. Various experts from different parts of the world were involved to identify local problems, such as differences between ethnic groups and rural/urban populations. Our incidence perspective of the burden offers a distinct advantage in terms of the potential for cancer prevention through intervention strategies against obesity, even after its onset. This work is especially important to inform public health policy and future research.
Developed countries most affected
In 2012, almost half a million or 3.6% of all new cancer cases in that year were due to overweight and obesity. Cancer due to overweight and obesity was more common in more developed countries (393,000 cases, 5.2%) than less developed countries (88,000 cases, 1.5%). Most cases attributable to overweight and obesity occurred in Northern America (111,000 cases or 6.3% of all cancers in the region) but the proportion of cancers due to overweight and obesity was highest in Eastern Europe (65,000 cases, 6.5% cancers in the region). In men, the countries with the highest cancer burden attributable to overweight and obesity were Czech Republic (5.5% of the country’s new cancer cases), Jordan (4.5%), UK (4.4%) and Malta (4.4%). Women in Barbados (12.7%), followed by Czech Republic (12.0%) and Puerto Rico (11.6%) were most affected. In the UK, 13,000 cases diagnosed in women in 2012 (or 8.2% of all new cancer cases) and 7,200 in men could be ascribed to overweight and obesity.
Higher burden among women
The proportion of new cancer cases attributed to overweight and obesity was greater in women (345,000 cases, 5.4%) than in men (136,000 cases, 1.9%). The obesity related cancer burden is higher among women mainly because common cancers of the female organs, such as post-menopausal breast cancer, have been associated with overweight and obesity. Cancers of the bowel, womb, and the breast in women after menopause, were responsible for approximately two-thirds of all cancers due to overweight and obesity in 2012.
How much can be prevented?
We calculated the number of cancer cases that could have been avoided had the obesity levels remained stable since 1982. We observed, one fourth (approximately 118,000 cases) of all cases currently attributed to overweight and obesity were due to the rising obesity epidemic since 1982; about 33,000 cases in men and 85,000 in women. The majority of those cases occurred in developed countries (80,000 cases), most notably in Northern America (42,000 cases).
These findings underpin the need for a global effort to abate the rising trends in overweight and obesity. In contrast to other important risk factors amendable for cancer prevention, such as smoking, the proportion of overweight and obese men and women is still rising in almost all countries. If this trend continues, it will likely increase the future burden of cancer.
This is a summary of our study, which is published online in The Lancet today.