A team of scientists have carried out a study to estimate the risk that people who have diabetes or obesity could develop cancer. This global study found that slightly more than 5% of cases worldwide were caused by diabetes or by being overweight (having a body mass index (BMI) of 25 or above). The scientists were from the Imperial College, London, the University of Kent and the World Health Organisation (WHO). The study has been published in peer-reviewed The Lancet Diabetes and Endocrinology and is available to read on an open access basis.
Scientists have linked being overweight and some types of cancer in previous studies. Recent cancers linked have included liver, breast and pancreatic cancer. This study, however, calculated the combined effect of both being overweight and being diagnosed with diabetes, on a global scale. Data was collected from 175 countries using information about BMI and diabetes from 2002 and BMI and cancer collected in 2012. The scientists were concerned because the rates of obesity and diabetes are both rising worldwide. The data from the study suggested, that incidences could rise by 20-30% by 2035.
The scientists collected data on rates of overweight people, who had diabetes globally. They also found data which connected numbers of 12 different types of cancer, which were already linked to diabetes or being overweight which had been diagnosed in 2012. They then used a comparative risk assessment to work out how many of those people who were overweight and diabetic in 2002 had gone on to develop cancer in 2012. The reliability of the data was enhanced because the scientists used data from the NCD Risk Factor Collaboration. This uses sources which collect the weight, height and measures of diabetes recorded rather than using self-reported data. The scientists used this data and information from the World Cancer Research Fund, the International Agency for Research on Cancer and estimates of cancer risk from previous studies, to help attribute a risk factor for each individual group of people and link the global proportion of cancers which were attributed to excess BMI and diabetes to the rise of BMI and diabetes from 1980 - 2002. These figures were then used to estimate future rates.
5.6% of cancer diagnosed in 2012 were attributed to diabetes and being overweight, but this average did not reveal the big differences between regions and types of cancer. Women were twice as likely as men, to be at risk of the disease from having diabetes and being overweight. They were more likely to develop breast or endometrial cancer while men were more likely to develop colorectal and liver cancer. People from high income western countries such as the UK (around 16%) were more likely to develop cancer related to diabetes or high BMI, while just over 30% of cases which were attributed to people being overweight may not have happened if the numbers of overweight people had stayed the same in 2002 as it was in 1980.
The decline of tobacco smoking and therefore the reduction in risk of developing cancer from it, means that attention will focus on other factors including high BMI. While the observational studies used were not all of the same quality, the scientists still felt that the results suggested that rising rates of diabetes and high BMI could lead to rates of certain cancers increasing too. This could place strain on worldwide health services. By encouraging people to maintain a healthy BMI, some of these cancers could be preventable.
Pearson-Stuttard J., et al., Worldwide burden of cancer attributable to diabetes and high body-mass index: a comparative risk assessment, The Lancet - Diabetes & Endocrinology, February 2018, Vol: 6, No: 2