Magnesium glycinate: why the form on the label matters

Two bottles sit side by side on the pharmacy shelf. Both say magnesium in large letters. One costs twice as much as the other, and the only visible difference is a word in smaller print: oxide on one, glycinate on the other. That word is most of what you are paying for, and for once the expensive version has the better argument.

Here is the piece nobody explains at the shelf: there is no such thing as plain magnesium in a capsule. The mineral is always bound to a partner compound, and the partner decides two things that matter to you. How much of the magnesium your body actually absorbs, and what the unabsorbed remainder does on its way through.

Oxide is the budget partner. It packs the most magnesium per gram, which makes the label number look generous, but your body absorbs only a small fraction of it. The rest stays in the gut, where unabsorbed magnesium draws in water. That is the classic laxative effect, and it is why oxide has a long and respectable career in an entirely different aisle. As a way of getting magnesium into you, it is mostly a way of getting magnesium through you.

Citrate is the sensible middle. Bound to the same acid that gives citrus fruit its bite, it is absorbed considerably better than oxide, and it is a fine everyday choice. Push the dose, though, and some of the bowel effect comes back.

Glycinate takes a different route entirely. Here the magnesium is chelated, bound to two molecules of glycine, the smallest amino acid, so the package can be handled partly the way the body handles amino acids rather than the way it handles mineral salts. Absorption is good, and it is among the gentler forms on the stomach. That combination is why glycinate has become the default recommendation for evening use: the last thing anyone wants from their wind-down routine is a surprise at 2am. The glycine partner is quietly interesting in its own right.

One label-reading note before you compare bottles. The number on the panel should be elemental magnesium, the mineral itself, not the weight of the whole compound, and the forms differ hugely in how much elemental magnesium they carry per gram. Two products can both say 200 mg and mean quite different things if one of them is counting the packaging. A trustworthy label names the form and states the elemental amount. If it does neither, that silence is information too; our label checklist covers the rest.

Does any of this matter if your magnesium intake is fine? Surveys keep suggesting it often is not: in New Zealand and overseas, adults keep coming up short of recommended intakes, largely because the richest food sources, whole grains, legumes, nuts and leafy greens, are the foods modern eating has trimmed back. Magnesium contributes to normal nervous system function, normal muscle function and the reduction of tiredness and fatigue, which is a careful way of saying the shortfall is worth closing.

In the Koru Nutrition range, the magnesium in Koru Sleep is the glycinate form, 226 mg per two-capsule serving, sharing the label with L-theanine, valerian and passionflower. The form was not the cheap choice. For an evening formula, it is the right one.