Supplement Stack for Runners: Iron, Magnesium, Electrolytes Explained

Every runner knows the feeling: legs heavy, focus fading, and a session that should feel crisp turns into a slog. While training volume and recovery are often the first suspects, the real culprit can be a silent shortfall in key micronutrients. For endurance athletes, the trio of iron, magnesium, and electrolytes isn’t just optional—it’s foundational. Understanding how these work together can transform how you feel on the road, on the trail, or on the track.

Running places unique demands on the body. Each footstrike causes mechanical stress, sweat losses deplete minerals, and the high energy turnover increases the need for certain vitamins and minerals. The best supplements for runners and cardio athletes address three core areas: oxygen delivery (iron), muscle relaxation and energy production (magnesium), and fluid balance (electrolytes). Without these, even the best training plan can hit a ceiling.

Magnesium contributes to normal muscle function and to the reduction of tiredness and fatigue.

Iron: oxygen delivery for endurance

Iron is a core component of haemoglobin, the protein in red blood cells that carries oxygen from your lungs to working muscles. During a long run, your oxygen demand can increase tenfold. If iron stores are low, your body struggles to keep up, leading to early fatigue, breathlessness, and a drop in performance.

The EFSA confirms that iron contributes to normal red blood cell and haemoglobin formation, as well as normal oxygen transport in the body. Including a well-absorbed form of iron—such as ferrous bisglycinate—can make a meaningful difference without the digestive upset common with cheaper forms.

Magnesium: the relaxation mineral

Magnesium is involved in over 300 enzymatic reactions, including energy production, protein synthesis, and muscle contraction. For runners, its role in muscle relaxation is critical. Magnesium contributes to normal muscle function.

The EFSA authorises the claim that magnesium contributes to normal muscle function and normal energy-yielding metabolism. Magnesium contributes to normal psychological function. Our Magnesium Multi provides 498 mg magnesium per 2 capsules (132% NRV).

Electrolytes: hydration beyond water

Sweat isn’t just water—it’s a cocktail of sodium, potassium, magnesium, and calcium. When you lose these faster than you replace them, your nervous system and muscles start to misfire. That’s when you feel dizzy, get cramps, or hit the wall.

Electrolyte supplements help maintain normal hydration status and muscle function. For runs lasting over 60 minutes or in warm conditions, plain water isn’t enough.

Our Electrolyte Multi contains sodium, potassium and chloride in a berry-flavour powder.

Timing and dosing matter. Here’s a practical framework based on current sports nutrition guidelines:

• Iron: Take on an empty stomach with vitamin C (e.g., a glass of orange juice) to enhance absorption. Avoid taking with tea, coffee, or calcium-rich foods within two hours. For most runners, 15–20 mg of elemental iron daily is sufficient, but blood testing is the gold standard for dosing.
• Magnesium Multi: 2 capsules, 1 to 4 times a day, as on the label.
• Electrolytes: Take 30 minutes before a run for longer sessions, or during/after for hot conditions or heavy sweating. Avoid over-supplementing on rest days—your diet provides enough for low-activity periods.

For those who prefer simplicity, our magnesium multi and electrolyte multi can be taken at different times of day without competing for absorption. Iron is best taken separately from both, ideally in the morning.

This stack is designed for runners and cardio athletes who:

• Train 4+ hours per week and experience lingering fatigue
• Are prone to muscle cramps or soreness after runs
• Sweat heavily or run in warm/humid conditions
• Follow a plant-based or low-meat diet (greater risk of low iron)
• Are female, especially during menstruation when iron losses are higher
• Iron contributes to normal oxygen transport in the body; magnesium contributes to normal muscle function.

Read our customer reviews.

While these nutrients are generally safe, certain groups need medical guidance:

• Iron overload conditions: Men and postmenopausal women should avoid iron supplementation without testing, as excess iron can be pro-oxidative. Haemochromatosis is a common genetic condition that causes iron accumulation.
• Kidney disease: Those with impaired kidney function should monitor potassium and magnesium intake carefully, as both are cleared by the kidneys.
• Heart conditions: If you take medications for blood pressure or arrhythmias, electrolyte changes can interact. Always check with a GP.
• Pregnancy: Iron needs increase, but magnesium and electrolyte doses may need adjustment. Seek professional advice.

Can I get enough iron, magnesium, and electrolytes from food alone?

In theory, yes—a varied wholefood diet can provide these nutrients. The free UK delivery makes it easy to keep your stack consistent.

Should I take these supplements before or after a run?

Timing depends on the nutrient. Electrolytes are best taken before and during long runs to prevent dehydration. Magnesium is ideal post-run or before bed to aid muscle relaxation. Iron is best taken on an empty stomach in the morning, away from training sessions, as exercise can temporarily reduce absorption.

Can I take iron, magnesium, and electrolytes together?

It’s not ideal. Calcium and magnesium compete for absorption, and iron absorption is reduced by calcium and magnesium. Take iron separately (morning) and magnesium/electrolytes later in the day. Our electrolyte multi and magnesium multi are designed to be taken at different times for maximum benefit.

Will magnesium make me sleepy during the day?

Magnesium supports relaxation, but it doesn’t cause drowsiness in standard doses.

How do I know if I’m deficient?

Common signs include persistent fatigue, muscle cramps, poor recovery, and heavy legs. The only definitive way is a blood test. Many GPs will check ferritin (iron stores) and magnesium levels. If you suspect a deficiency, start with a conservative dose and monitor how you feel over 4–6 weeks.

Do I need to cycle these supplements?

Iron can be cycled if stores are adequate—many runners take it for 3 months then test again. Magnesium and electrolytes are safe for long-term daily use at recommended doses. Listen to your body and adjust based on training load, climate, and diet.

We believe supplements should be straightforward, evidence-based, and made to the highest standards. You’ll always know exactly what you’re taking.

Free UK delivery on every order. Creatine increases physical performance in successive bursts of short-term, high intensity exercise (3 g a day); our 5 g scoop provides 4.4 g creatine.

Iron, magnesium, and electrolytes aren’t trendy—they’re essential. For runners and cardio athletes, they support the three pillars of performance: oxygen delivery, muscle function, and hydration.

Start with one or two, listen to your body, and build from there. If you’re ready to try a stack that’s backed by science and made in the UK, explore our electrolyte multi and magnesium multi today.

This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any new supplement regimen, especially if you have an underlying health condition or are taking medication. Individual needs vary, and blood testing is recommended to guide supplementation. All health claims are authorised under the UK Nutrition and Health Claims Register. Vitadefence UK, 3rd Floor, 86-90 Paul Street, London EC2A 4NE.