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For western high-income countries such as the UK, an estimated 15% to 16% of cancers could be avoided by preventing diabetes, obesity or excess weight (defined as a Body Mass Index [BMI] greater than 25). A high BMI was responsible for almost twice as many cancers as diabetes.
Around 5.7% of cancers globally in 2012 were attributable to diabetes or high BMI. Because obesity is increasing globally, this number may rise by 25% by 2035.
Although the links between high BMI, diabetes and cancer have been known for some time, this study presents the first calculations of attributable risk for 175 countries. This represents the proportion of cancers that could be prevented if the risk factors were eliminated.
The researchers call for more to be done to prevent obesity and diabetes.
Why was this study needed?
Diabetes and high BMI are leading causes of death and ill health globally and are on the increase in most countries. In 2014, diabetes affected 9% of men and 8% of women. In 2016, worldwide 38.5% of men and 39.2% of women had high BMI, equivalent to around 2.01 billion adults. Rates are even higher in the UK: 65% of men and 58% of women in 2014 had high BMI.
The International Agency for Research on Cancer recognises a causal association between high BMI and 12 different cancers. High BMI is a risk factor for type 2 diabetes, which in turn is a risk factor for some cancers.
Given the rising levels of both high BMI and diabetes, this study aimed to estimate the impact of these conditions individually and together on cancer risk.
What did this study do?
This study uses previously published data, pooled from observational studies, on cancer risk associated with weight and diabetes. The 12 different cancers with the strongest association were chosen, and then the proportion of cancers of each type which could be attributed to diabetes or high BMI (the attributable risk) was calculated. The researchers collected data on the number of people with a BMI over 25 and diabetes in 2002 from 175 countries. They then looked at rates of cancer 10 years later in 2012.
The studies included in the meta-analyses for diabetes had applied rigorous adjustment to control for potential confounding factors, including BMI. This allowed the researchers to separate out the risk attributable to high BMI from that due to diabetes and also consider these risk factors acting together or independently.
What did it find?
- A total of 5.7% of all incident cancers in 2012 were attributable to being overweight and having diabetes, corresponding to 804,100 new cases, although these findings fluctuate between groups of people, regions and cancers.
- There were 187,600 (24.5%) of 766,000 cases of liver cancer and 121,700 (38.4%) of 317,000 cases of endometrial cancer attributable to diabetes and a high BMI.
- Individually, having a high BMI (544,300 cases) was responsible for twice as many cancer cases as diabetes (293,300 cases).
- 25.8% of diabetes-related cancers (75,600 cases), and 31.9% of high BMI related cancers (174,040 cases) might have been avoided if the prevalence of these risk factors had remained at levels from the 1980s.
- Being overweight was estimated to cause 16.4% of cases of cancer in men and 15.0% in women in high-income western countries compared to 2.7% and 3.0% respectively in South Asia.
What does current guidance say on this issue?
The World Cancer Research Fund reports strong evidence for high BMI as a risk for developing 11 different types of cancer. Possible reasons include storing too much fat, which encourages the body to produce growth hormones which can promote the growth of cancer cells. Body fat also stimulates an inflammatory response, which may contribute to the development of several cancers.
The International Agency for Research on Cancer warns obesity is a risk factor for more cancer sites than previously established, reinforcing the benefits of maintaining a healthy body weight.
What are the implications?
The global average of 5.6% of cancers diagnosed in 2012 linked to weight and diabetes hides some variability between countries. For example, 38.2% of 792,600 cancer cases occurred in high-income western countries such as the UK.
This study provides the clear message that rising rates of excess BMI and diabetes may lead to increasing levels of certain cancers placing increasing strain on healthcare services everywhere.
The authors highlight population-based interventions to prevent and treat unhealthy weight and diabetes as a UK and global priority.
Citation and Funding
Pearson-Suttard J, Zhou B, Kontis V, et al. Worldwide burden of cancer attributable to diabetes and high body mass index: a comparative risk assessment. Lancet Diabetes Endocrinol. 2018. 6(6): E6-15.
This study was funded by the National Institute for Health Research and the Wellcome Trust.
Bibliography
NCD Risk Factor Collaboration (NCD-RisC). Worldwide trends in body-mass index, underweight, overweight, and obesity from 1975 to 2016: a pooled analysis of 2416 population-based measurement studies in 128·9 million children, adolescents, and adults. Lancet. 2017;390(10113):2627-42.
NHS England. Diabetes Prevention Programme . London: NHS England; 2016.
NICE. Type 2 Diabetes prevention: population and community-level interventions. PH35. London: National Institute for Health and Care Excellence; 2011.
World Cancer Research Fund. Obesity, weight and cancer risk. London: World Cancer Research Fund; 2016.
World Health Organization. International Agency for Research on Cancer Identifies eight additional cancer sites linked to overweight and obesity. Press Release No. 247. Lyon: World Health Organization; 2016.
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