Magnesium oxide dominates supermarket shelves and barely crosses the gut wall. Glycinate, malate, and threonate are different molecules with different reads. Form matters.

Which magnesium form actually gets absorbed

Organic magnesium salts (glycinate, citrate, malate, taurate) absorb at roughly 25 to 40 percent in human studies. Magnesium oxide sits closer to 4 percent. That gap is the entire reason most people taking a "magnesium" supplement feel nothing.

The mineral itself is identical. What changes is the carrier molecule it rides in on, and that carrier dictates whether your gut releases it, how much makes it into circulation, and where in the body it tends to act.

If you only remember one thing: skip oxide. It is cheap to manufacture, which is why it fills NZ pharmacy shelves, but it is the worst-absorbed common form on the market.

The six forms worth knowing

Magnesium oxide. High elemental magnesium per capsule, low bioavailability. Useful as a laxative. Not useful for raising tissue magnesium. This is what most $12 supermarket bottles contain.

Magnesium citrate. Decent absorption, mild laxative effect at higher doses. A reasonable general-purpose form. Common in NZ pharmacies and worth choosing over oxide if that is what is in front of you.

Magnesium glycinate (or bisglycinate). Magnesium bound to the amino acid glycine. High absorption, gentle on the gut, calming profile because glycine itself is an inhibitory neurotransmitter. The default choice for sleep, stress, and general repletion.

Magnesium malate. Bound to malic acid, an intermediate in the cellular energy cycle. Often chosen for daytime use, fatigue, and muscle complaints. Absorption is good.

Magnesium threonate. Engineered to cross the blood-brain barrier more readily than other forms. Marketed for cognition. The human evidence is thinner than the marketing, but the mechanism is real. Expensive.

Magnesium taurate. Bound to taurine. Often used in cardiovascular and blood-pressure contexts because taurine has its own vascular and electrolyte effects. Less common in NZ but available online.

Match the form to the goal

Sleep, anxiety, restless legs, muscle twitches at night: glycinate. Take it 60 to 90 minutes before bed. Most people feel something within a week.

Daytime fatigue, muscle soreness, fibromyalgia-style complaints: malate. Take it with breakfast or lunch. Stack with adequate protein and B vitamins.

Constipation: citrate or, if you must, oxide. Both pull water into the bowel. This is a side effect being used as the effect.

Cognitive load, shift work, mental fatigue: threonate is the one with the brain-penetration argument. Pricey. Glycinate covers most people first.

Blood pressure, palpitations, cardiovascular focus: taurate is the form with the most coherent rationale, though we work alongside your GP for anything cardiac.

Most people who tell us "magnesium did nothing for me" were taking oxide. Switch the form, change the result.

What the NZ supplement aisle actually offers

Walk into a Christchurch pharmacy and the shelves skew heavily to oxide and citrate, often in mixed-form blends that bury 5 mg of glycinate next to 300 mg of oxide and label the bottle "magnesium complex." Read the per-capsule breakdown, not the front of the box.

Pure single-form glycinate, malate, and taurate are easier to find through NZ practitioner brands and online retailers than on supermarket shelves. Threonate is almost always imported.

A few practical notes for buying here:

  • "Elemental magnesium" is the number that matters. A 1000 mg capsule of magnesium glycinate contains around 100 to 140 mg of actual magnesium. That is the dose.
  • Most adults benefit from 200 to 400 mg of elemental magnesium daily from supplementation, on top of food.
  • Split the dose if you go above 200 mg at once. Absorption per dose drops as the dose climbs.
  • Food still matters. Leafy greens, nuts, seeds, dark chocolate, and legumes carry magnesium with the cofactors that help it work. Across our 2,846-food dataset, the top contributors for most NZ eaters are pumpkin seeds, almonds, spinach, and black beans.

When supplementation is not the real answer

Magnesium status is shaped by what you absorb and what you lose. High alcohol intake, chronic stress, heavy sweating, certain diuretics, proton pump inhibitors, and poorly managed type 2 diabetes all increase losses. No form of magnesium fixes a leaking bucket.

Serum magnesium is also a poor marker. It stays in normal range while tissue stores deplete, because the body prioritises blood levels. RBC magnesium is a better read, and we order it through your GP when the clinical picture warrants it.

Across 1,380+ clients, the pattern is consistent: people who sleep poorly, train hard, drink regularly, or eat low-vegetable diets are the ones who feel the biggest shift from getting magnesium right. People already eating 6+ serves of plants daily often notice less, because they were not deficient to begin with.

What to do this week

  • Check your current magnesium bottle. If the active ingredient is oxide, replace it.
  • Choose glycinate for evening use, malate for morning use, or run glycinate alone if you want one bottle.
  • Aim for 200 to 400 mg of elemental magnesium daily from supplementation, split across two doses if needed.
  • Add two magnesium-dense foods to your weekly shop: pumpkin seeds and either spinach or silverbeet.
  • If you are on diuretics, PPIs, or diabetes medication, raise magnesium status with your GP before changing doses.