A spattering of studies has linked cancer-related radiation therapy with diabetes or obesity, so a team of researchers from six American research hospitals and the University of Alberta in Canada went searching for a broad pattern. Sure enough, they found that treatment with abdominal irradiation, total body irradiation or cranial irradiation increased the odds of developing diabetes by 90 percent, according to a study to be published in Tuesday's edition of the Archives of Internal Medicine. The researchers focused on a group of 8,599 people who were alive at least five years after being diagnosed with one of several cancers -- leukemia, central nervous system tumors, Hodgkin lymphoma, non-Hodgkin lymphoma, renal tumors, neuroblastoma, soft-tissue sarcomas or bone tumors -- before the age of 21. In a survey, the cancer survivors revealed whether they had taken an oral diabetes medication or insulin for more than a month in the previous two years. The same questions were asked of 2,936 of the survivors' healthy siblings. Among the survivors, 2.5 percent said they took medication for diabetes. That compared with 1.7 percent of the siblings. After adjusting for age, gender, race/ethnicity, household income, health insurance status and body mass index, the researchers found that the cancer survivors were 1.8 times more likely to develop diabetes. They also were more likely to get it at a younger age -- 57 percent of the survivors with diabetes were under the age of 35, compared with 35 percent of the siblings with the disease. The risks were highest for cancer survivors who received total body irradiation or abdominal irradiation. Those who were treated with TBI were 12.6 times more likely than the siblings to develop diabetes, and those who had abdominal radiation had more than triple the risk, the study found. The researchers also compared cancer survivors who got radiation therapy with other cancer survivors who didn't. The ones who got TBI were 7.2 times more likely to develop diabetes, and those who had abdominal irradiation were 2.7 times more likely to develop the disease. Cranial irradiation wasn't associated with an increased risk of diabetes. The team also discovered that survivors who were diagnosed with cancer before the age of 5 were 2.4 times more likely to get diabetes than survivors who were diagnosed in their late teens. Experts aren't sure why radiation therapy might cause diabetes, but they have several theories. Perhaps the radiation damages the part of the pancreas responsible for making and secreting insulin, the hormone needed to metabolize sugar. Alternatively, the radiation could alter the hormones in adipose tissue, perhaps causing insulin resistance. The researchers noted that their risk calculations could be overstated if cancer survivors were more likely than their siblings to get a check-up that would lead to a diabetes diagnosis. 