Nearly 6% of cancers attributable to diabetes, high BMI

UK researchers have revealed that diabetes and high body-mass index (over 25 kg/m²) were the cause of 5.6% of new cancer cases worldwide in 2012 — equivalent to 792,600 cases.

Estimates suggest that 422 million adults have diabetes and 2.01 billion adults are overweight or obese. Both high BMI and diabetes are risk factors for various types of cancer, potentially due to biological changes caused by diabetes and high BMI — such as high insulin, high sugar levels, chronic inflammation and dysregulated sex hormones such as oestrogen — having adverse effects on the body. And with these two risk factors becoming increasingly widespread, the proportion of attributable cancers is set to grow further.

With this in mind, scientists from Imperial College London conducted what is claimed to be the first study to quantify the proportion of cancers attributable to diabetes and high BMI. Published in The Lancet Diabetes & Endocrinology, 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, combining this with data on high BMI and on diabetes. They then matched the datasets by age group and sex to take account of age differences using diabetes and BMI data from 2002 to calculate cancer incidence in 2012 attributable to these risks.

When considered individually, 544,300 cases were attributable to high BMI (equivalent to 3.9% of all cancers) and 280,100 were attributable to diabetes (2%). Most of the cases occurred in high-income western countries (38.2%), while the second-largest proportion occurred in east and southeast Asian countries (24.1%).

Although cancers are still less common in some low- and middle-income countries than in high-income nations, the population of these countries experienced particularly large impacts from diabetes and high BMI. For example, 9–14% of all cancer cases in Mongolia, Egypt, Kuwait and Vanuatu were due to high BMI and diabetes. Meanwhile, Tanzania, Mozambique and Madagascar had the lowest proportion of cases attributable to high BMI and diabetes.

Globally, the growing number of people with diabetes between 1980 and 2002 led to 77,000 new cases of attributable cancers in 2012 (a 26.1% increase). Similar increases in the number of people with high BMI led to 174,040 new cases of weight-related cancers (a 31.9% increase) 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.

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, with the researchers estimating that the proportion of related cancers will grow by more than 30% in women and 20% in men on average. With this in mind, the study authors suggest that clinical and public health efforts should focus on identifying preventative and screening measures for populations and for individual patients — particularly through the implementation of effective food policies.

Furthermore, 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.

Image credit: ©stock.adobe.com/au/Andrey Popov