Vitamins and minerals
Normal Magnesium Levels: What 0.7 to 1.0 Really Tells You
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed August 20265 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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UK labs report serum magnesium against a range of 0.7 to 1.0 mmol/L. There is no adult age chart. The catch is that only about 1% of your magnesium sits in blood, with roughly half of it locked in bone, so a normal result does not rule out a low store.
Not sure which markers you need? Build your test →Your magnesium comes back at 0.74 mmol/L. In range, no flag, nothing to see. You are still cramping at night and still waking at 3am. So was the test wrong, or were you?
Neither, and the reason is worth five minutes. Magnesium is a mineral your muscles and nerves run on. The blood test for it is useful, but it answers a narrower question than most people think.
1. What is a normal magnesium level in the UK?
One range covers every adult age. Gloucestershire Hospitals NHS Foundation Trust pathology publishes it as 0.7 to 1.00 mmol/L for serum or plasma magnesium. Other UK labs sit very close to that.
| Result | How it reads |
|---|---|
| Below 0.7 mmol/L | Low. Worth a GP conversation. |
| 0.7 to 1.0 mmol/L | Inside the reference range. |
| Above 1.0 mmol/L | High. Usually supplements or reduced kidney clearance. |
The band is narrow, which is the first clue. Your body defends blood magnesium hard, and it has a large reserve to defend it with.
2. Why a normal result can still miss a low store
Because blood holds almost none of your magnesium. An adult carries roughly 25 grams of it. Around half to 60% is in bone. Most of the rest sits inside muscle and organs. Blood and the fluid around your cells hold about 1%.
So the test samples the smallest compartment, and it is the one your body works hardest to keep steady. Pull magnesium out of the diet and bone releases some to hold the blood level up. The scientific review behind the reference intakes is direct about the consequence.
“Serum magnesium concentration has not been validated as a reliable indicator of body magnesium status.”
— Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride
That is not a reason to skip the test. It is a reason to read it for what it is. A result of 0.74 mmol/L means your blood level is being held. It does not promise your stores are full.
3. What the blood test is genuinely good for
Three things, and they are worth knowing before you decide whether to test.
- Catching a genuinely low level. A result under 0.7 mmol/L is real and actionable.
- Explaining stubborn calcium or potassium results. Low magnesium can keep both of those low, and correcting it can settle them.
- Checking you are not overdoing supplements. High magnesium usually means high intake, or kidneys clearing less.
Gloucestershire pathology frames the test around absorption and clearance: magnesium in blood is held by a balance between what your gut takes in and what your kidneys pass out. That is why it gets checked when malabsorption or kidney trouble is suspected.
4. What a low magnesium result means
Under 0.7 mmol/L, the useful question is why. Low magnesium is rarely just about diet. These are the common drivers:
- Long-term stomach acid medication, especially proton pump inhibitors.
- Diuretics, or some chemotherapy drugs.
- Poorly controlled diabetes, which pulls magnesium into urine.
- Coeliac disease, Crohn's or another cause of poor absorption.
- Heavy or sustained alcohol use.
- Prolonged diarrhoea or vomiting.
Take a low result to a GP rather than to a supplement shelf. Our guide on the signs of low magnesium covers the symptom side, and taking too much magnesium covers the other end.
5. Which blood test reports your magnesium
The marker is magnesium, reported in mmol/L. If you take a magnesium supplement, leave it off for 24 hours before the sample so you measure your baseline rather than this morning's dose.
Helvy's Vitamins & Minerals panel (£159) reports magnesium alongside iron, ferritin, transferrin saturation, vitamin B12, folate and vitamin D. That grouping is the point. Cramp, poor sleep and fatigue have several possible causes, and iron and B12 explain far more of them than magnesium does.
Magnesium also appears in our General Energy & Wellness panel (£149). One honest limit: we measure magnesium in serum, not inside red cells, so the caveat above applies to our result too. To pick your own markers, the build-my-test tool walks you through it.
READY TO TEST?
See your magnesium next to the markers it gets blamed for
Helvy's home blood tests report magnesium with plain-English context, and with the iron and B12 markers that explain the same symptoms. Samples are processed by UKAS-accredited UK labs.
Frequently asked questions
What is a normal magnesium level in the UK?
UK labs report serum magnesium against roughly 0.7 to 1.0 mmol/L, and the same range applies at every adult age. Ranges vary slightly between labs, so read your number against the one printed on your own report.
Can you be low in magnesium with a normal blood test?
Yes. Only about 1% of body magnesium is in blood, and roughly half sits in bone, which releases some to defend the blood level. The scientific review behind the dietary reference intakes states that serum magnesium has not been validated as a reliable indicator of body magnesium status.
Is a magnesium of 0.75 mmol/L low?
It is inside the reference range, near the lower end. That is not the same as a deficiency, and it is not proof your stores are full either. If you have symptoms, the more useful step is checking iron, ferritin, B12 and thyroid alongside it.
What causes low magnesium?
Long-term stomach acid medication, diuretics, poorly controlled diabetes, coeliac disease or Crohn's, heavy alcohol use, and prolonged diarrhoea or vomiting. Diet alone is a less common cause in the UK. A low result is worth taking to a GP.
Should you stop magnesium supplements before the test?
Leaving them off for 24 hours gives you a cleaner baseline. A dose taken shortly before the sample can lift the reading. Do not stop anything a clinician has prescribed without asking them first.
Is there a magnesium chart by age?
Not for adults. UK labs apply one adult range from 18 upward. Newborns and young children have their own ranges. Any adult age chart online is showing averages rather than targets.
Related guides
Magnesium Blood Test UK
What the test measures, and when it is worth doing.
Signs of Low Magnesium
The symptoms people notice, and what else explains them.
Can You Take Too Much Magnesium?
Where the upper limit sits, and who needs to be careful.
Which Magnesium Should I Take?
Citrate, glycinate, taurate and the rest, compared honestly.
Vitamin D Levels by Age UK
The other mineral marker people misread, decade by decade.
Blood Test Reference Ranges UK
Why normal on a lab report is a population range, not a target.