5.6% of worldwide cancer cases attributable to high BMI, diabetes

Diabetes and high body mass index (BMI) caused 5.6 percent of new cancer cases worldwide in 2012, accounting for 792,600 total cases, according to a study published in The Lancet Diabetes and Endocrinology journal. Individually, high BMI—at least 25 kilograms per square meter—was responsible for twice as many new cancer cases as diabetes.

Cancer research organizations have concluded there is a causal association between high BMI and several forms of cancer. In addition, diabetes has been recognized as a risk factor for colorectal, pancreatic, liver, gallbladder, breast and endometrial cancer, according to lead study author Jonathan Pearson-Stuttard, BM, BCh, and colleagues.

Since high BMI and diabetes often overlap as risk factors, the researchers felt it was important to develop the first estimate of the global cancer burden that is attributable to each of these factors individually and combined.

The authors gathered data on 12 types of cancer from 175 countries and incorporated a 10-year lag time to associate high BMI and diabetes with downstream cancer cases. In other words, they used estimates of global diabetes and high BMI prevalence from 2002 to calculate how many new cancer cases in 2012 were caused by these factors.

According to Pearson-Stuttard et al., 26.1 percent of all cancer diagnoses attributable to diabetes and 31.9 percent of all cancers attributable to high BMI in 2012 were due to an increase in the prevalence of those risk factors from 1980 to 2002.

“Given the continued rise in … these risk factors since 2002, the attributable cancer burden is likely to continue to increase in coming decades,” Pearson-Stuttard and co-authors wrote, adding public health efforts to combat obesity and diabetes are needed to slow this trend.

About 38 percent of the new cancer cases attributable to high BMI or diabetes occurred in high-income Western countries, while Asia and southeast Asia had the second largest proportion (24.1 percent).

Liver cancer and endometrial cancer contributed the highest number of new cases caused by diabetes and high BMI. The authors estimated 24.5 percent of liver cancer diagnoses (187,600 total cases) and 38.4 percent of endometrial cancer cases (121,700 total) were attributable to those factors.

“Proposed biological mechanisms underlying the link between diabetes, high BMI, and cancer include hyperinsulinaemia, hyperglycaemia, chronic inflammation, and dysregulation of sex hormone activity,” they wrote. “Insulin itself could be oncogenic, and results from several analyses showed that people with hyperinsulinaemia were at increased risk of breast and colorectal cancer irrespective of their BMI. Prospective studies and large-scale consortia with more accurate assessments of adiposity, diabetes, and metabolic health, which incorporate molecular tools, will be needed to draw conclusions about the underlying mechanisms that link diabetes, high BMI, and cancer, and inform clinical interventions.”

Pearson-Stuttard and colleagues acknowledged the 10-year lag period was an imperfect measure to account for past risk factor exposure.

In a related editorial, Yikyung Park, ScD, and Graham A. Colditz, MD, MPH—both with Washington University School of Medicine in St. Louis—suggested that lag-period technique may lead to an underestimation of the cancer burden associated with high BMI.

“Although the 10-year lag takes into account the process of carcinogenesis and cumulative exposure over time, it understates the importance of early life exposure, especially from high BMI, on cancer. Emerging evidence suggests that high BMI in late adolescence and young adulthood is directly related to risk of cancer in old age,” Park and Colditz wrote.

The editorial authors also said the link of diabetes to cancer could have been underestimated because the researchers excluded bladder, kidney and esophageal cancer and myeloma—all cancers that might be associated with diabetes.