Endurance athletes such as runners and cyclists are used to hearing injunctions to drink enough water. While staying hydrated is important, there are times when you can have too much water.

Last summer, for example, I began experiencing unusual muscle cramping in my hands and legs long after I finished a run, even the next day. Following the usual advice, I increased my water intake and ate bananas, which are full of potassium. That did not fix the problem. I then heard Jordan Metzl, a sports medicine specialist at the Hospital for Special Surgery in New York, describe how he had nearly crashed during his first Ironman race. It was a hot day, Dr Metzl recalled, and he was saved by a bearded bystander who was handing out raw salt.

If you follow medical news, you have probably heard the campaigns in the UK and the US warning about eating too much salt. It is true that there is often a lot of salt added to prepared food, and sodium can raise your blood pressure, which can lead to a heart attack.