When it’s hot outside, your body keeps cool by sweating. But you don’t just lose water in the process: You also lose electrolytes like sodium, calcium and potassium that are crucial to keep your body functioning well.

Sports drinks, hydration powders and tablets promise to help you replenish your electrolytes. But when do you actually need them, and are they the best source? “People always say ‘just drink Gatorade,’” said Dr. Elan Goldwasser, a sports medicine physician at NewYork-Presbyterian. “But the truth is, it’s so much more than that.”

Why do I need electrolytes?

The body is like a large and complex electrical circuit, Dr. Goldwasser said. Electrolytes — which also include magnesium, chloride, phosphorus and bicarbonate — carry an electrical charge that enable our nerves, muscles and cells to communicate with each other and to function properly, he said.

Among their roles, electrolytes help regulate how much water is inside and outside cells and blood vessels; help maintain a regular heartbeat and help ensure that muscles contract and relax properly, Dr. Goldwasser said.

But to do their job, electrolytes have to be kept in balance. For most people, eating a nutritious diet and drinking water when you feel thirsty are enough, said Dr. Vishnu Potluri, an assistant professor of medicine at the Hospital of the University of Pennsylvania. But imbalanced electrolytes, whether you have too much or too little, “can both be problematic,” he said.

What happens if I lose too many electrolytes?

If you’re sweating a lot and not replenishing fluids, you run the risk of dehydration, which throws your electrolytes out of balance, experts said.