Researchers at Oxford Population Health have found that people living with diabetes have higher risks of developing six types of cancer, and that these associations cannot be explained by other common risk factors for cancer and diabetes. The study is published in the Journal of the National Cancer Institute.
Type 2 diabetes affects hundreds of millions of people worldwide and has been linked to higher risks of several cancers. However, it was uncertain whether these links are due to diabetes itself. Many previous studies have struggled to disentangle the effects of diabetes from those of shared risk factors, especially obesity, or to rule out confusion between cause and effect where early signs of cancer may lead to a diabetes diagnosis.
In this study, researchers analysed data from 2.2 million adults enrolled in the Million Women Study, the China Kadoorie Biobank, and the UK Biobank. Participants were followed for up to 20 years through national cancer and death registries to track new cancer diagnoses and cancer deaths.
The study examined whether people with diabetes were more likely to develop or die from 15 different types of cancer. The researchers also assessed the extent to which the observed associations of diabetes with cancer could be explained by shared risk factors (such as obesity), or by the greater likelihood of a diabetes diagnosis in those being investigated for cancer symptoms.
They also investigated whether the results varied by country, method of diabetes detection, and participant characteristics such as age, sex, body weight, smoking, and alcohol use.
Key findings:
- Diabetes was associated with increased risks of 11 out of 15 site-specific cancers in combined analyses of UK and Chinese adults;
- The strongest associations observed were with the risk of developing liver cancer, which was roughly doubled in those with diabetes, followed by pancreatic (62% higher risk) and bladder cancer (44% higher risk);
- The risks were similar in UK and Chinese populations except for liver cancer, where the risk was 2.58 times higher in the UK population and 1.61 times higher in the Chinese population;
- The excess risk of liver cancer associated with diabetes was more pronounced among individuals with higher BMI or heavier alcohol consumption, suggesting these factors may modify the effect of diabetes on risk.
Bowen Liu, DPhil student at Oxford Population Health and lead author of the paper, said ‘These findings highlight the importance of preventing diabetes, through weight management and other strategies, in reducing the risk of developing several common cancers. Preventing diabetes could be especially important for lowering liver cancer risk among individuals who are overweight or heavy drinkers, as the benefits may be substantially greater in these groups.’
The researchers found that the association between having diabetes and risk of cancers of the liver, pancreas, stomach, colon and rectum, bladder, and leukaemia remained even after taking account of other factors that may have influenced their risk and the potential for cancer symptoms to lead to a diabetes diagnosis.
For several cancers, including endometrial, kidney, oesophageal adenocarcinoma, and postmenopausal breast cancer, the associations between diabetes and an increased risk of these cancers were substantially weakened after taking into account measures of body fatness and other factors, suggesting that diabetes may not be directly responsible for an increased risk of these cancers.
Although diabetes was linked to a 22% lower risk of prostate cancer, it was linked to a 25% higher risk of death from prostate cancer; this may be because lower levels of prostate-specific antigen (a marker of prostate cancer) in men with diabetes may lead to lower detection rates of less aggressive prostate cancer.