"Your magnesium is fine," the doctor says, turning the screen so you can see. The number sits neatly inside the range. Then she moves on to your iron.

Nobody in that room mentions where the range came from. The cut-off for "low" traces back to a survey of Americans that ended in 1974. It recorded what was common in that crowd, and nobody tied it to who stayed well.

Can a blood test show low magnesium?

Only late. Less than one per cent of your magnesium is in your bloodstream. Nearly all of it lives in bone and muscle, and when you run short, your skeleton quietly lends some out. The figure on the screen barely moves.

Three trailers and a surprise

Canada has looked properly once. Statistics Canada runs a clinic built from three semi-trailers, which sets up near a town and invites the neighbours in. In 2012 and 2013, thousands of volunteers climbed the steps and rolled up a sleeve.

Three white clinic trailers parked in a Canadian town, where a national health survey collects blood samples.

Graded on that old American curve, as many as one adult in six still landed under the line. Health Canada's scientists published the tally with an unusually frank sentence. Their findings, they wrote, "raise suspicions" of deficiency across the Canadian population.

How do I know if I get enough magnesium?

Look at dinner. When Health Canada ran the sums on a national food survey from 2004, more than a third of adults fell short on meals alone.

The mineral has a favourite address. One atom of it sits at the centre of every molecule of chlorophyll, the pigment that makes a leaf green. Dark greens carry it for that reason, and seeds, nuts and beans hoard it too. A mill does the opposite: when the bran and germ come off wheat, much of it leaves with them.

On the plate Magnesium
Daily target, women 31 to 50 320 mg
Pumpkin seeds, 28 g 156 mg
Almonds, 28 g 80 mg
Cooked spinach, 125 ml 78 mg
Foods high in magnesium: a leafy green salad topped with pumpkin seeds and almonds.

None of that is expensive. A handful of seeds over a salad covers a surprising share, and brown rice in place of white helps too.

For the weeks when supper is toast, a supplement is fair cover. NOW Magnesium Citrate blends three forms in a small softgel, and its listing covers muscle function, bones and teeth. Salus Magnesium is a fruit-and-chamomile liquid, measured by the capful, for anyone who refuses pills. Natural Calm is an unflavoured powder that fizzes in a warm mug and suits the evening kettle. Show the label to a pharmacist first, especially alongside prescriptions.

Your doctor will turn that monitor toward you again next year. By then the pumpkin seeds will have lived on the counter for months.

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Questions we get

How much magnesium is safe to take as a supplement?
Health Canada sets the adult upper limit at 350 mg a day from supplements. Magnesium in food and water does not count toward it. Loose stools are the usual first sign of too much. Anyone with kidney disease should ask a doctor before taking any.

Is there a more accurate magnesium test?
One exists, but it is impractical. It involves an IV drip of magnesium and collecting your urine for 24 hours, and the Linus Pauling Institute calls it too invasive and costly for routine use. Red blood cell tests are sold as an upgrade but have not been proven more reliable.

Can medication lower my magnesium?
Yes. Acid-reflux drugs called proton pump inhibitors can lower it after long use, usually more than a year, and some water pills increase losses in urine. Magnesium can also block certain antibiotics and osteoporosis drugs, so space them at least two hours apart.

This article is journalism, not medical advice. Talk to your doctor or pharmacist before starting a supplement, particularly if you are pregnant, breastfeeding, taking medication or living with kidney disease. Figures checked 9 November 2026.

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