If you could recommend one supplement that is key for every endurance athlete to take, what would it be?

Magnesium and creatine are good supplements to take for endurance athletes. Magnesium helps with recovery, and creatine helps with bones and muscles. It also has benefits for brain health.
 
Transcript: "There are loads that I could actually suggest. Magnesium is a super obvious one. But I think you know that. So I'll just leave that. Creatine is not so obvious, but that would be one that immediately springs to mind, because it helps with recovery, helps your bones and muscles. And it's not often one associated with endurance. And in fact, because of the potential for fluid gain, a lot of people avoid it. But three grams a day will saturate the cells, allow for a bit of recovery of the bone and muscle. And it's super good for your brain, too."