You wake up at night with a brutal calf cramp, and the next morning you immediately google "magnesium." Understandable, because magnesium is the mineral blamed for almost everything: cramps, fatigue, poor sleep, stress. But before you stock up on supplements, there is one thing you should honestly know about magnesium and blood tests.
My view: a standard magnesium blood value is a mediocre gauge, because most of your magnesium sits inside your cells and bones. A "normal" result therefore does not fully rule out a deficiency. That does not make it a useless test, but it is a test you must read alongside your symptoms.
What does magnesium actually do?
Magnesium is involved in hundreds of processes: muscle contraction, nerve conduction, energy production and bone building. It works closely with calcium and potassium. Because it is so widely used, a deficiency causes varied, non-specific complaints.
Symptoms of a magnesium deficiency
The complaints are broad and fit other deficiencies too, so they do not automatically point to magnesium.
- Muscle cramps and twitches
- Fatigue and weakness
- Tingling and a restless feeling
- Restless legs
- Palpitations, especially with a large deficiency
- Irritability and poor sleep
Which test fits your question?
There are two ways to measure magnesium, and they answer different questions.
| Test | What it measures | When useful |
|---|---|---|
| Magnesium (serum) | Magnesium in your blood | Quick, broad screening; widely available |
| Magnesium intracellular | Magnesium inside your cells | When in doubt while serum is normal |
Because most magnesium sits inside your cells, the serum value can stay normal for a long time while your stores fall. The intracellular measurement sometimes gives a fuller picture, but the result should always be assessed in the context of your symptoms.
Causes and risk groups
- A one-sided diet: little vegetables, nuts and wholegrain products
- Heavy alcohol use: increases magnesium excretion
- Prolonged stress: may raise your needs
- Gastrointestinal conditions: reduced absorption
- Certain medicines: diuretics and long-term use of acid blockers
- Older adults: lower intake and absorption
Where do you find magnesium?
The Voedingscentrum (Netherlands Nutrition Centre) lists these as rich sources:
- Nuts and seeds: almonds, pumpkin seeds
- Green leafy vegetables: spinach
- Wholegrain products and legumes
- Dark chocolate
A varied diet provides enough magnesium for most people. The Gezondheidsraad (Health Council of the Netherlands) sets recommended amounts (around 300 to 350 mg per day for adults), but a deficiency from diet alone is not a given in healthy people. A supplement is mainly useful with a confirmed deficiency or on a doctor's advice.
Which supplement form should you choose?
If you and your doctor decide on a supplement, the form matters for tolerability. The rule of thumb: well-absorbed organic forms cause gut complaints less readily than cheap inorganic forms.
- Magnesium oxide: cheap and high in magnesium per tablet, but absorbed poorly and more likely to cause diarrhoea. It is also used as a laxative, which is telling.
- Magnesium citrate: better absorbed, a common choice for mild deficiencies.
- Magnesium bisglycinate: often well tolerated, including by people with a sensitive gut.
Start low and build up slowly: if you get loose stools, you are probably dosing too high. Taking high doses on your own is especially inadvisable with reduced kidney function, because your kidneys then clear the surplus less well. In that case, always consult your doctor first.
How do you read your result?
A serum value within the reference range does not automatically mean all is well, because blood holds only a fraction of your total magnesium. Conversely, a genuinely lowered serum value is a clear signal and should always be viewed alongside your symptoms and medication. If you use diuretics or long-term acid blockers, mention it, as those can structurally affect your value. A single result is a snapshot; when in doubt, your doctor can repeat the measurement or consider the intracellular variant.
Frequently asked questions
Does magnesium help against cramps?
With a confirmed deficiency, supplementing can reduce complaints. Without a deficiency, the effect on cramps is uncertain and variable. A blood value helps decide whether supplementing makes sense.
Can I get too much magnesium?
Not through food. Through supplements, a high dose can cause gut complaints such as diarrhoea. Stick to the recommended dose and consult your doctor if in doubt.
Which other minerals are often checked alongside?
With vague complaints, magnesium, calcium and potassium are often viewed together because they work closely. A broad complete metabolic panel maps that balance in one go.
Can stress lower my magnesium?
Prolonged stress can raise your need for magnesium, and heavy stress often goes hand in hand with eating less well and sleeping worse. A direct, large effect on your blood value is not proven, but with ongoing complaints it can make sense to measure your magnesium alongside your lifestyle rather than guessing.
Want a focused magnesium measurement? Check your magnesium value or build a custom blood test. For the full picture on fatigue and minerals, read our overview of vitamin and mineral deficiency. Every result at Vitalcheck is reviewed by a registered doctor. A blood value is not a diagnosis: discuss symptoms and treatment with your GP.
Sources
- Gezondheidsraad (Health Council of the Netherlands). Dietary reference values for vitamins and minerals. 2018.
- Voedingscentrum (Netherlands Nutrition Centre). Magnesium. Accessed 2026.
- Thuisarts.nl / NHG. Magnesium. Accessed 2026.
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