Magnesium: Effects, Forms, Requirements and Deficiency

Updated: October 2026

Magnesium is one of the most popular supplements of all. Which form is meant for what, and how much you really need, can be cleared up with a few numbers.

What does magnesium do in the body?

Magnesium is involved in more than 300 enzymatic reactions. It plays a role in normal muscle function, nerve signal transmission, energy metabolism and bone health. About half of the body's stores sit in the bones.

As a supplement, magnesium is often used for calf cramps, stress or tiredness. With a genuine deficiency it may help; without one, the effect is usually small. Calf cramps also have many causes, so if they happen often, have the cause checked by a doctor.

Magnesium works closely with calcium: calcium triggers muscle contraction, magnesium supports relaxation. The mineral is also involved in protein formation, blood pressure regulation and blood sugar metabolism. That's why a long-term deficiency can affect the whole body.

Which form of magnesium is best?

It depends on tolerance and purpose. Organic compounds such as citrate or glycinate are generally absorbed better than inorganic ones such as oxide. Magnesium glycinate is considered particularly gentle on the stomach because it less often causes diarrhoea.

When buying, compare the amount of pure magnesium, not the weight of the compound. What matters is the figure for "elemental magnesium" per serving.

How much magnesium do you need per day?

The DGE gives estimated values for adequate intake for adults aged 25 and over of about 350 mg for men and 300 mg for women. Younger adults are slightly higher, and pregnant and breastfeeding women have a slightly increased need. For additional magnesium supplements, the EFSA gives a tolerable upper limit of 250 mg per day, because higher amounts more often cause diarrhoea.

With food alone, an overdose is practically impossible in healthy people, as the kidneys excrete excess magnesium.

Your needs rise temporarily: with heavy sweating, intense exercise, during pregnancy and with some medications. A balanced diet covers this in most cases, though. If you eat wholemeal bread, oats, nuts and vegetables every day, you often reach the recommended range without a supplement.

Which foods are high in magnesium?

Good sources are pumpkin seeds, nuts, oats, whole-grain products, legumes, green vegetables and some mineral waters. The following values are rounded reference figures per 100 g.

A handful of pumpkin seeds or almonds (30 g) already provides around a third of the daily requirement. You can read more about oats in the article Oats: Calories, Nutrition and Recipes. Vegetables and freshly pressed juices also contribute a little to your intake, but they're not a main source.

When is the best time to take magnesium?

That depends on your goal. Many people take magnesium in the evening because it is associated with relaxation. A specific time of day is not scientifically proven. Regular intake matters more, ideally with or after a meal, which is gentler on the stomach.

• Split higher amounts into two doses, which improves absorption.
• Take magnesium two to three hours apart from iron, zinc and calcium.
• With certain antibiotics and thyroid medication, leave a bigger gap and ask at the pharmacy.

A simple plan: breakfast with oats and nuts, vegetables and legumes at lunch, a handful of seeds in the afternoon. This often gets you to the reference value with normal food alone. A supplement is then an extra for special days, not a permanent programme.

How can you tell if you have a magnesium deficiency?

Possible signs are muscle cramps, twitching, tingling, tiredness or palpitations. These complaints are non-specific, though, and often have other causes. A blood test shows only a small part of the body's stores, so a deficiency can't always be reliably confirmed. Risk groups include people with gastrointestinal conditions, heavy alcohol consumption, diabetes, or who take diuretics and proton pump inhibitors.

You'll find more on the topic of deficiency in the article What to Do About Nutrient Deficiency?

A common misconception: being tired doesn't automatically mean too little magnesium. Lack of sleep, iron deficiency, stress or a thyroid disorder are just as possible. So have persistent tiredness checked by a doctor before you take supplements long term.

What side effects can magnesium have?

With supplements, diarrhoea is the most common side effect, along with nausea and stomach cramps. If that happens, reduce the dose or switch to glycinate. People with weak kidney function should only take magnesium after talking to a doctor, because the mineral can build up in the blood.

Very high doses can cause a drop in blood pressure, muscle weakness and heart rhythm disturbances. This almost only affects people with impaired kidney function or an overdose over a longer period. Stick to the recommended intake on the packaging.

Matching picks from frank.

Magnesium from food is the simplest foundation. If you'd rather drink your vegetables and fruit, you'll find a selection in our cold-pressed juices that complements meals with nuts and whole grains nicely.

You might also like

• Which Minerals Do You Need?
• Which Nutrients Does the Body Need Daily?
• What to Do About Nutrient Deficiency?

Frequently asked questions about magnesium

Which magnesium helps with calf cramps?

Magnesium citrate and glycinate are absorbed well. If cramps are frequent, the cause should be checked by a doctor, as magnesium doesn't help in every case.

Can I take magnesium every day?

In usual doses of up to about 250 mg extra per day, this is generally unproblematic for healthy people. With kidney disease, medical advice is needed.

Does magnesium before bed make sense?

Some take it in the evening, but a better effect at that time isn't proven. Choose the time that fits well into your day.

How long does it take for magnesium to work?

With a deficiency, symptoms often improve after a few days to weeks. Without a deficiency, you can hardly expect a noticeable change.

Is magnesium from mineral water enough?

Some waters contain over 100 mg per litre and contribute noticeably. The levels vary a lot, so it's worth checking the label.

Note: This article is for general information and is not a substitute for medical or therapeutic advice. If you have complaints, pre-existing conditions, are pregnant or take medication, please talk to your doctor first.