By itself, coconut water is not ideal for prolonged or endurance exercise, without additional carbohydrate or electrolyte supplementation.

FORBES: The Truth Behind The Coconut Water Craze

While taking seriously the growing evidence for potential risks of endurance exercise, Thompson said he isn't advising his patients against it.

WSJ: The Exercise Equivalent of a Cheeseburger?

Publicizing the potential dangers of endurance exercise could give recreational athletes an argument for resisting pressure to go longer and harder.

WSJ: The Exercise Equivalent of a Cheeseburger?

Yet by all accounts, dosage is no less relevant to exercise than to any other medical treatment, and for years the endurance-athletics movement has prompted words of caution from none other than Kenneth Cooper, the Dallas physician widely credited with launching the aerobics movement nearly half a century ago.

WSJ: Endurance Sports: Studies on Older Endurance Athletes Suggest the Fittest Reap Few Health Benefits