Extremely obese people are needing a much higher dose of radiation during x-ray examinations than people of normal weight, thus increasing their risk of cancer, new research has shown. The University of Exeter and Musgrove Park Hospital in England led the study of more than 600 patients who had undergone surgery for weight loss.

The researchers found 630 patients with an available history of radiation dose in x-rays carried out between 2007 and 2015. The patients in the study had a body mass index of up to 50, indicating they were severely obese and nearly twice the weight they should be for their height. They had all undergone procedures such as the fitting of gastric bands, gastric sleeves or gastric bypasses at Musgrove Park Hospital, a national center of excellence for bariatric surgery and diagnostic imaging.

The team discovered that obese patients received much higher doses of radiation during x-ray than normal weight people, which is necessary due to the increased amount of tissue to be imaged. The study, published in the Journal of Radiological Protection, concluded that the overall risk of cancer caused by the extra radiation was more than double (153%) that of normal-weight people undergoing x-ray. However, the risk of cancer from x-ray is low. From 2015 to 2016, 22.6 million x-ray procedures were carried out in England—and up to 280 cancers may have been related to x-ray related radiation dose.

Karen Knapp, associate professor of musculoskeletal imaging at the University of Exeter, who oversaw the study, says: “X-rays are an extremely important diagnostic tool, and radiographers do their utmost to minimize the risk to patients. However, our findings highlight the implications of increased radiation doses in severely obese patients. Although the risk of cancer from x-ray is very low, we urgently need more research in patients who are overweight and obese, so we can understand how to minimize doses in this group and feed into far more robust guidelines around radiation, in turn to minimize that risk.”

Currently, there are no guidelines around how to minimize radiation doses in obese patients, study officials say. Now, the researchers believe this is needed to minimize risk of cancer exposure in this group.