A study of more than 1 million South Koreans suggests diabetes can raise the risk of developing and dying from several types of cancer, including digestive-tract tumors. This is not the first study to suggest such a link, but it sheds more light on exactly how diabetes might contribute to cancer. Diabetes is often linked to obesity, and obesity is known to increase the risk of cancer. Yet few of the study participants were overweight, so the researchers think high blood sugar levels -- another hallmark of diabetes -- might also be involved. The highest risks for developing cancer and dying from it were found in people with the highest blood sugar levels, the South Korean researchers found. The study appears in Wednesday’s Journal of the American Medical Association.