Sodium vs. Magnesium: What's really important?

Ask ten athletes what mineral they take for cramps — nine will say: magnesium. Ask the same ten how much sodium they lose daily — most won't know. That's the problem.

Magnesium has excellent marketing. Sodium has science on its side. And the truth, as is often the case, lies not in an either-or, but in understanding what each mineral truly does and when it's truly needed.

What Sodium Does in the Body

Sodium is the most abundant electrolyte in the human body. It is found mainly outside the cells — in the blood and tissue fluid — where it regulates fluid balance. Where sodium goes, water follows. This makes it primarily responsible for blood volume, blood pressure, and the distribution of fluid between tissues and the bloodstream.

For athletes, this is directly relevant: sodium contributes to normal muscle function and nerve conduction.¹ Those who have too little sodium cannot efficiently retain fluid in the bloodstream — the result is poorer blood flow to the muscles, an increased heart rate, and an earlier feeling of exhaustion.

And critically: Sodium is by far the electrolyte you lose the most of when sweating. You lose 500–1,500 mg of sodium per liter of sweat. You might lose 150–300 mg of potassium, and hardly 10–40 mg of magnesium. Sodium dominates the loss equation, accounting for 80–90%.

What Magnesium Does in the Body

Magnesium is an intracellular mineral — it primarily works inside the cells. It is involved in over 300 enzymatic processes, including energy production (ATP synthesis), protein synthesis, and the regulation of muscle contraction. Magnesium contributes to normal muscle function and normal nervous system function.¹

Magnesium acts as an antagonist to calcium: while calcium triggers muscle contraction, magnesium is involved in relaxation. A deficiency can lead to muscles relaxing less effectively — which explains the connection to cramps.

The body stores about 60% of magnesium in the bones; the rest is in muscle cells and other tissues. This means that a magnesium deficiency develops slowly and insidiously — not acutely during a single training session.

Why Magnesium is Overrated

Magnesium has gained enormous popularity in recent years — as a miracle cure for cramps, poor sleep, stress, and exhaustion. Part of this is justified. A large part is marketing.

The problem: magnesium deficiency is less common in the German population than often claimed, according to the National Consumption Study. Most people who take magnesium supplements do not have a clinical deficiency — they have a sodium deficit that feels similar.

Furthermore: Magnesium loss through sweating is minimal. Even during an intensive 2-hour workout, you lose hardly 50–80 mg of magnesium — an amount that a handful of pumpkin seeds or a few squares of dark chocolate can easily compensate for. No handful of pumpkin seeds can compensate for the sodium loss from the same session — up to 3,000 mg.

Why Sodium is Underrated

Sodium has an image problem. Decades of campaigns against salt as a risk factor for high blood pressure have led to sodium being generally perceived negatively by many people.

This recommendation applies to the general population with a predominantly sedentary lifestyle and high consumption of processed foods. For athletes who sweat regularly, it is misleading. Someone who trains 1–2 hours daily and loses 1,000–2,000 mg of sodium in the process is in a fundamentally different physiological situation than someone who does not engage in any sport.

Research is clear: In active people, low sodium levels correlate with decreased performance, muscle cramps, nausea, and in extreme cases, hyponatremia — a dangerously low blood sodium level documented in endurance athletes.

What Really Helps with Cramps

Cramps during exercise are reflexively attributed to magnesium deficiency. Science is more nuanced.

Current research distinguishes two main causes of exercise-associated muscle cramps: the classic electrolyte theory and the newer neuromuscular theory, which views excessive nerve activity as the trigger. Both factors likely play a role — and electrolytes are part of both explanations.

What practice shows: Athletes who suffer from regular cramps and specifically optimize their sodium balance often report significant improvement — even if they had previously taken magnesium. This suggests that sodium deficiency is the actual cause in many cases, but magnesium remains the more visible adjustment screw.

The Honest Ranking for Athletes

If you have to prioritize, this is the order:

1. Sodium — the largest losses, the most direct impact on performance and hydration, most underestimated.

2. Potassium — also important for muscle function and heart rhythm, moderate losses in sweat, easily supplemented through diet.

3. Magnesium — important for long-term health and recovery, low losses in sweat, basic needs usually met by a whole food diet, supplementation makes sense with intense training and a poor nutritional foundation.

This does not mean that magnesium is unimportant. It means that you should not neglect sodium while you are taking care of magnesium.

When You Need Both

A complete electrolyte profile makes sense. Sodium and magnesium are not mutually exclusive — they complement each other. A good supplement contains both, in sensible amounts. The only question is which one you prioritize when there's an acute need.

Quick rule of thumb: If you experience cramps or feel fatigued during or immediately after exercise — think sodium first. If you are working on sleep, recovery, or general exhaustion long-term — magnesium is a useful supplement.

Conclusion

The sodium vs. magnesium discussion is not a question of important or unimportant — both minerals perform essential functions. But it is a question of priority. Sodium dominates your sweat losses, regulates your fluid balance, and has the most direct impact on your athletic performance. Magnesium is the patient long-term worker — indispensable, but rarely the acute bottleneck.

Those who keep both in mind are well-prepared. Those who only think of magnesium neglect the more important mineral.