After seeing three marathoners with colon cancer in a span of about six months, oncologist Dr Timothy Cannon could not help but wonder if it was more than a coincidence.Could there be a connection between the cancer and the gastrointestinal (GI) problems many runners experience during long events?“Runner’s ischaemia is well described,” says Cannon, a researcher from the Inova Schar Cancer Institute in the US state of Virginia, referring to a condition that develops during prolonged endurance exercise, when blood is diverted away from the digestive system and towards the working muscles.This can leave the gut temporarily short of blood supply, leading to cramps, nausea, diarrhoea and, in some cases, bleeding.“A lot of [endurance runners] have had GI issues after running. I wondered whether there could be a connection [with colon cancer] if you’re having so much cell turnover from cell death after these long runs?”Oncologist Dr Timothy Cannon says people who have bleeding or a lot of cramping or discomfort after they run should get checked out. Photo: Dr Timothy CannonHow was the connection explored?