Vitamins and minerals
Magnesium by Age: One Range for a Whole Life
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed September 20266 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.
QUICK ANSWER
There is no magnesium chart by age. UK labs use one serum range, 0.7 to 1.0 mmol/L, from four weeks old onward. A study of 441 adults aged 24 to 98 found serum magnesium had no link to age at all, while the magnesium measured inside muscle cells clearly fell.
Not sure which markers you need? Build your test →You are 68, the cramps keep coming, and your magnesium came back at 0.78. You went looking for a chart by age, expecting older adults to have a lower target. There is no such chart.
That absence is not an oversight. It turns out to be the most useful thing about this marker, once you know why.
1. What is a normal magnesium level by age?
UK labs split magnesium exactly once, and it happens before you are a month old.
| Age | Range (mmol/L) | Notes |
|---|---|---|
| Under 4 weeks | 0.6 to 1.0 | Newborns sit slightly lower at the bottom. |
| 4 weeks and older | 0.7 to 1.0 | One range, for the rest of your life. |
North Bristol NHS Trust publishes the same adult figures, 0.70 to 1.00 mmol/L. So a reading of 0.78 is read identically at 28 and at 88.
The obvious question is whether that is right, or whether labs have simply never looked. Somebody did look.
2. Does serum magnesium fall as you get older?
No, and the measurement is unusually clean. Researchers on the Baltimore Longitudinal Study of Aging tested 441 adults aged 24 to 98. They measured magnesium two ways at once: the ordinary blood test, and a scan reading magnesium inside living muscle.
“Total serum Mg was not significantly associated with age in the whole cohort.”
— Baltimore Longitudinal Study of Aging, magnesium and muscle function
The blood number held flat across seven decades, in men and in women separately. UK labs are right to use one range.
The magnesium inside the muscle did not hold flat. That is the half of the finding worth your attention.
3. What does fall with age, and why it is hidden
In the same 441 adults, magnesium measured inside muscle cells fell clearly with age. The association was strong enough to reach statistical significance in the whole group and in both sexes.
There is a plain reason the blood test misses it. Less than 1% of the magnesium in your body is in your blood at all. Roughly half sits in bone and most of the rest inside cells.
Your body also guards the blood level tightly. When intake drops, magnesium is pulled out of the bone reserve to hold the serum number steady. The reading stays normal while the store behind it quietly empties.
So read a normal serum magnesium for what it is. It rules out a clear shortage in the blood. It does not prove your stores are full, and it is not a reason to dismiss symptoms that point at magnesium.
4. How much magnesium you actually need
The NHS gives one figure for men and one for women, and does not raise either with age. Adults aged 19 to 64 need 300mg a day for men, 270mg a day for women.
On supplements, the NHS is more specific than most sources and worth quoting directly. The Department of Health and Social Care position is that “having 400mg or less a day of magnesium from supplements is unlikely to cause any harm”.
Above that, the first effect is dull rather than dangerous. The NHS notes that high doses over 400mg taken for a short time can cause diarrhoea.
Our guide on taking too much magnesium covers where those limits come from, and which form to take compares the salts sold in UK shops.
5. What pushes serum magnesium down
If age is not the answer, these usually are. They matter more in later life because more of them apply at once.
- Long-term proton pump inhibitors, such as omeprazole.
- Diuretics, often called water tablets.
- Poor absorption, including coeliac disease and Crohn's.
- Heavy or sustained alcohol use.
- Poorly controlled blood sugar, which raises urinary losses.
- A diet light on nuts, seeds, pulses and green vegetables.
Read that list again with a 70-year-old in mind. Several are ordinary features of later life rather than anything unusual, which is why magnesium is worth checking even though the range never moves.
Our guide to omeprazole and blood tests covers the first one in detail, since it is the most common and the most missed.
Migraine is the other reason people come looking for their magnesium. If that is you, read the evidence on magnesium, B2 and CoQ10 for migraine before you commit to a supplement, alongside whether magnesium is worth taking for migraine at all.
6. Which blood test reports your magnesium
The marker is magnesium, reported in mmol/L. Helvy's Vitamins & Minerals panel (£159) reports it with iron, ferritin, transferrin saturation, vitamin B12, folate and vitamin D. The General Energy & Wellness panel (£149) reports it with CRP, cortisol, thyroid, kidney and cholesterol markers.
Magnesium on its own is a thin result. Read next to iron, B12 and folate it becomes useful, because those four explain a lot of the same tiredness and the same cramps.
One honest limit, and it is the point of this guide. A serum magnesium result measures the blood, not your stores. No routine UK blood test measures intracellular magnesium, so treat a normal result as one piece of evidence rather than a verdict.
For the range itself, our normal magnesium levels guide goes further. To pick your own markers, the build-my-test tool walks you through it.
READY TO TEST?
See magnesium next to the markers it shares symptoms with
Helvy's home blood tests report magnesium with the iron, B12 and vitamin D markers that explain the same tiredness, and say what each one means. Samples are processed by UKAS-accredited UK labs.
Frequently asked questions
What are normal magnesium levels by age?
UK labs use 0.6 to 1.0 mmol/L under four weeks old, then 0.7 to 1.0 mmol/L for everyone older. There is no separate adult or elderly range, and no chart by decade.
Does magnesium go down with age?
In the blood, no. A study of 441 adults aged 24 to 98 found total serum magnesium was not significantly associated with age. Magnesium measured inside muscle cells did fall with age in the same people.
Is a magnesium of 0.78 normal?
It sits inside the 0.7 to 1.0 mmol/L range UK labs publish, in the lower half. Check the range printed on your own report, since labs vary slightly. A normal result does not rule out low stores.
Can a blood test show magnesium deficiency?
It shows blood magnesium, which is under 1% of your total. Your body holds that level steady by drawing on bone, so a normal serum result can sit alongside depleted stores. It is one piece of evidence, not the whole answer.
How much magnesium do adults need?
The NHS gives 300mg a day for men aged 19 to 64 and 270mg a day for women. Neither figure rises with age. Nuts, seeds, pulses and green vegetables are the main food sources.
How much magnesium is safe to take as a supplement?
The NHS states that having 400mg or less a day of magnesium from supplements is unlikely to cause any harm. Above that, high doses taken for a short time can cause diarrhoea. Check with a clinician if you have kidney problems.
Does omeprazole lower magnesium?
Long-term proton pump inhibitors are a recognised cause of low magnesium, and omeprazole is the most commonly prescribed one in the UK. It is worth knowing about if you have taken it for months or years.
Which blood test includes magnesium?
The NHS does not include it in a standard U&E panel, so it is usually added on request. Helvy reports magnesium in the Vitamins & Minerals panel and the General Energy & Wellness panel.
Related guides
Normal Magnesium Levels UK
The range itself, and what sits either side of it.
Magnesium Blood Test UK
What the test measures and when it is worth doing.
Signs of Low Magnesium
The symptoms a normal blood result does not rule out.
Can You Take Too Much Magnesium?
Where the NHS 400mg supplement figure comes from.
Which Magnesium Should I Take?
Glycinate, citrate and the rest, compared.
Blood Test Results by Age UK
Which markers genuinely shift with age, and which do not.
Related panels
Keep reading