What should you look out for when buying electrolytes?
For endurance exercise lasting longer than an hour and a half, a drink containing sodium and carbohydrates is worthwhile; for daily use or shorter sessions, an electrolyte supplement adds nothing for most people. Always check whether the product is certified and pay attention to the concentrations on the label, not the brand name.
Buying electrolytes starts with the question: what do you need them for? For most people who simply move around or exercise for less than an hour and a half, a separate electrolyte supplement adds nothing. A review states it explicitly: for healthy people, a normal daily diet is more than sufficient to compensate for what is lost through sweat and urine.
If you are going to exercise intensively for longer than 60 to 90 minutes, a sports drink containing both sodium and carbohydrates is worthwhile. Check the label: the drink should contain approximately 0.5 to 0.7 grams of sodium per litre and 4 to 8% carbohydrates. Drink 600 to 1200 mL of it per hour during exercise. Cheap own-brand drinks that meet these values work just as well as an expensive brand; what matters is the concentration, not the name on the packaging. Drinks that contain only electrolytes without carbohydrates retain fluid less effectively than the combination of both.
If you want to maximise the effect on fluid retention, oral rehydration solutions (ORS, such as those used for diarrhoea) deliver the strongest results. In research, people retained significantly more fluid after such a solution than after plain water, while a regular sports drink in that same study showed no difference from water. ORS is not intended as a sports drink, however; it has a different composition.
Be critical of products that add extra amino acids or other ingredients. One small study, funded by the manufacturer itself, found no difference in running time performance compared with water or a regular sports drink. The claim about fewer muscle cramps in that same study is based on the self-reporting of twenty participants and is not financially independent: that is too little to rely on.
Supplement regulation is also weaker than you might think. What appears on the label does not always match what is inside the packaging. Check whether the product is certified by an independent body that tests its contents. And finally, pay attention to your own sweat rate: people who sweat a great deal or produce salty sweat have different needs during the same exercise session than someone who sweats little. A one-size-fits-all approach does not suit everyone.
This answer is based on multiple randomised studies, a clinical study, and several reviews from major sports organisations such as the ACSM and ADA. The evidence for the combination of sodium and carbohydrates in endurance sport is fairly consistent. The study on the amino acid electrolyte drink was small (20 participants) and was sponsored by the manufacturer, which limits its reliability. The recommendations on personalisation and supplement safety come from reviews and are less well supported by experimental evidence.