Diabetes and high body mass index (BMI) were responsible for 5.6 percent of cancer cases around the world in 2012, according to a British study – and the trend is worsening.
The study, published today in The Lancet Diabetes & Endocrinology journal is said to be the first to quantify the proportion of cancers attributable to diabetes and high BMI (i.e. overweight people with a BMI of 25 or over).
The researchers estimated that high BMI was responsible for nearly 550,000 cases (3.9 per cent of all cases), and diabetes 280,000 cases (2 per cent), with most cancers occurring in high-income western countries. With the prevalence of diabetes and high BMI continuing to grow worldwide the researchers say the proportion of cancers caused by the two factors is likely to increase in coming decades unless action is taken.
Globally, liver cancer and endometrial cancer contributed the highest number of cancer cases caused by diabetes and high BMI (24.5% and 38.4% of cases respectively).
The study says estimates suggest that 422 million adults have diabetes and 2.01 billion adults are overweight or obese around the world. Both high BMI and diabetes are risk factors for various types of cancer potentially due to resulting biological changes such as high insulin, high sugar levels, chronic inflammation, and oestrogen level changes – having adverse effects on the body.
“As the prevalence of these cancer risk factors increases, clinical and public health efforts should focus on identifying preventive and screening measures for populations and for individual patients,” said research Dr Jonathan Pearson-Stuttard of Imperial College London.
The study assessed the increase in new cases of 18 cancers based on the prevalence of diabetes and high BMI in 175 countries between 1980 and 2002.
The authors gathered data on the incidence of 12 types of cancer from 175 countries in 2012. They combined this with data on high BMI and on diabetes from ten years earlier to calculate cancer incidence in 2012 attributable to these two risks.
Most of the cancer cases attributable to diabetes and high BMI occurred in high-income western countries (38.2%), and the second largest proportion occurring in east and southeast Asian countries (24.1%).
However, the number of cases of different cancers varied globally, and in high-income Asia Pacific and east and southeast Asian countries liver cancer caused 30.7 percent and 53.8 per cent of cases respectively, while in high-income western countries, central and eastern Europe, and sub-Saharan Africa breast and endometrial cancers contributed 40.9 per cent of cancer cases.
Globally, the growing number of people with diabetes between 1980 and 2002 led to a 26.1 per cent increase in diabetes-related cancers. Similar increases in the number of people with high BMI led to a a nearly 32 per cent increase in weight-related cancers over the same time.
Low- and middle-income countries across Asia and sub-Saharan Africa saw the largest increases in cancers due to diabetes and overweight and obesity, as the levels of diabetes and high BMI in these regions increased substantially between 1980 and 2002. For example, the number of diabetes-related cancers grew by 88 per cent in 2012 for men in south Asia, increasing from 3500 cases in 1990 to 6600 cases in 2012. Similarly, cancer cases attributable to high BMI in women in sub-Saharan Africa increased by 80 per cent – from 5400 cases in 1990 to 9700 cases in 2012.
The proportion of cancers related to diabetes and high BMI is expected to increase even further globally as the prevalence of the two risk factors increases. Using projected prevalence of diabetes and high BMI for 2025 compared with prevalence in 2002, the researchers estimate that the proportion of related cancers will grow by more than 30 per cent in women and 20 per cent in men on average.
Dr Pearson-Stuttard adds: “Increases in diabetes and high BMI worldwide could lead to a substantial increase in the proportion of cancers attributable to these risk factors, if nothing is done to reduce them. These projections are particularly alarming when considering the high and increasing cost of cancer and metabolic diseases, and highlight the need to improve control measures, and increase awareness of the link between cancer, diabetes, and high BMI.” 
The authors note that the 10-year lag between risk factor exposure and cancer development is a simple estimate of how long it takes for cancer to develop so may not include full exposure to the risk. There is growing evidence suggesting that diabetes is also related to myeloma, bladder, kidney, and oesophageal cancer, meaning the study may underestimate the burden of cancers due to diabetes.
Cancers associated with diabetes and high BMI
Diabetes is associated with colorectal, pancreas, liver, gallbladder, breast and endometrial cancers.
High BMI is associated with multiple myeloma, colorectal, gallbladder, pancreas, kidney, liver, endometrial, breast, ovarian, stomach cardia, thyroid cancers and oesophageal adenocarcinoma.