Electrolytes and sports hydration: when you really need them

What electrolytes are and what they do

Electrolytes are minerals that, dissolved in the body, carry an electrical charge: sodium, potassium, magnesium, chloride and calcium. They are essential for basic functions — the balance of fluids inside and outside cells, the transmission of nerve impulses and muscle contraction. When you train and sweat, you lose water and, with it, some electrolytes. The question is not whether they are important (they are), but when you need to actively replace them and when your body and your food already take care of it.

What you actually lose when you sweat

Sweat is mostly water with sodium. Sodium is by far the electrolyte you lose most: between about 0.2 and 2.3 g per liter of sweat depending on the person (McDermott et al., 2017), and the "salty sweaters" sit at the top of that range, and you can tell by the white marks on their clothes. Potassium, magnesium and chloride are lost in much smaller amounts. That is why, when replacement is genuinely needed, sodium is the protagonist; the rest is covered by a normal meal after training.

Do you need electrolyte drinks?

The short answer: almost never for the gym, sometimes for endurance sport. It depends on the context:

• You do NOT need them: sessions under an hour, normal intensity, mild weather. Water is plenty.
• They DO help: long efforts (over an hour), very intense work, heat and humidity, or if you are a heavy sweater.
• Special cases: two sessions in the same day, long competitions, or if you struggle to recover the fluid you lose.

Sodium: the one that really matters

Of all the electrolytes, sodium is the only one that usually deserves attention in sport. Besides replacing what you sweat out, sodium helps your body retain the fluid you drink instead of eliminating it, which improves hydration in long efforts. That is why sports drinks contain sodium and not just sugar. For most people, however, the salt in food covers the need with room to spare; only with heavy, prolonged sweating does adding sodium during exercise make sense.

Drinking too much is dangerous too

The "drink lots of water" message has sunk in so deeply that it sometimes becomes a risk. In very long events, drinking excessive amounts of plain water can dilute the sodium in your blood and cause hyponatremia, a serious condition that in extreme cases is fatal. The international consensus on exercise-associated hyponatremia (Hew-Butler et al., 2015) makes it clear: the rule is not "the more the better" but drink to thirst, and in very prolonged efforts pair the water with sodium. Neither dehydrated nor overhydrated: the middle ground.

Do electrolytes prevent cramps?

It is the most widespread myth. For decades cramps were blamed on dehydration or electrolyte shortage, but the modern evidence is far more nuanced: a good part of exercise-associated cramps seem to come from neuromuscular fatigue — overloaded, tired muscles misfiring — rather than a salt deficit. Replacing sodium can help those who sweat a great deal, but for most people the best antidote to cramps is not overreaching on intensity, training progressively and resting well.

Where to get electrolytes without supplements

Your diet is your best electrolyte drink. You do not need sachets to cover your daily needs:

• Sodium: table salt and salty foods (cheese, olives, bread). Rarely lacking in a Western diet.
• Potassium: banana, orange, potato, tomato, legumes, leafy vegetables.
• Magnesium: nuts, seeds, leafy greens, legumes, dark chocolate.
• Calcium: dairy, sardines, tofu, broccoli and leafy greens.

Hydrating well — neither too little nor too much — is one of those habits that add up day after day, and the easy part to control. For water you do not need an app: a bottle in sight and the color of your urine are enough. For food, Renzy lets you log each plate with a photo, which gives you the rest of the picture: what you eat and how you progress.