This theory has been put forward, but it's important to point out that there is no real evidence yet. An alternative theory is diet, which is also the leading theory for increasing incidences in non-athletes. Highly processed, calorie dense foods have been on the watchlist for a while, and ultra endurance athletes have a special need for these to satisfy their caloric requirements. It could also be a combination of these factors or something else that was missed entirely so far.