What the Words in Brackets on Your Supplement Label Mean

Turn over almost any supplement and you will find words in brackets after each nutrient. Cholecalciferol. Bisglycinate. Menaquinone. Ascorbic acid. Most people's eyes slide straight past them.

Those brackets are the most useful part of the label. They tell you which version of a nutrient you are buying, and the versions are not equivalent. Two products can list the same milligrams of zinc and deliver very different amounts to your body.

Here is how to read them.

Why the form matters at all

A vitamin or mineral cannot sit in a tablet as a lone atom. It has to be bound to something to stay stable. What it is bound to determines how easily your digestive system can absorb it.

The cheap forms are usually cheap because they are simple compounds that are harder to absorb. The better forms cost more to produce, and manufacturers who use them tend to say so, because it is one of the few genuine quality differences you can verify from the outside.

Minerals

Zinc

You will see oxide, sulphate, citrate, gluconate or bisglycinate.

Zinc oxide is the cheapest and the most common in budget multivitamins. It is poorly soluble, which is the root of the problem.

Zinc bisglycinate binds zinc to the amino acid glycine. Chelated forms like this are generally better absorbed and gentler on an empty stomach. It costs considerably more, which is exactly why it appears less often. Ours is bisglycinate.

Magnesium

Magnesium oxide is by far the most common and the least well absorbed. It is also the form most likely to have a laxative effect, which is not a coincidence, since what is not absorbed stays in the gut and draws water in.

Citrate, glycinate and malate are all better absorbed. If a product lists just "magnesium" with no form, it is almost certainly oxide.

Iron

Ferrous sulphate is standard and effective but is the form most associated with constipation and stomach upset. Ferrous bisglycinate is gentler. If iron has been a problem for you before, the form is worth checking rather than giving up on iron.

Calcium

Carbonate is cheap and needs stomach acid to be absorbed, so it should be taken with food. Citrate is absorbed with or without, which matters more with age since stomach acid production falls.

Vitamins

Vitamin D

Cholecalciferol is D3, the form your skin makes from sunlight. Ergocalciferol is D2, from fungi, and is generally considered less effective at raising blood levels.

Conventional D3 comes from lanolin in sheep's wool, so vegan products use lichen derived D3 instead. Ours is cholecalciferol.

Vitamin K

Phylloquinone is K1, the sort in leafy greens. Menaquinone is K2, from fermented foods, and is much rarer in a normal UK diet. K2 is the more expensive one, so a product listing only "vitamin K" is usually K1. Ours is menaquinone.

Vitamin E

This one has a genuinely useful tell. d-alpha tocopherol is the natural form. dl-alpha tocopherol, with the extra letter, is synthetic and less well retained by the body. One character on a label, a real difference in what you get.

Vitamin A

Retinol or retinyl palmitate is preformed vitamin A, ready to use. Beta carotene is the plant precursor, which your body converts at a variable and often inefficient rate. Ours is listed as retinol.

B12

Cyanocobalamin is the most common and most stable. Methylcobalamin is the form marketed as more bioavailable. Both work for most people, and the debate between them is livelier online than the evidence really supports. Ours is cyanocobalamin.

Folate

Folic acid is the synthetic form used in fortification and in the supplements recommended before pregnancy, and it is the form all that guidance is based on. Methylfolate is the active form. For pregnancy specifically, follow the NHS advice on folic acid rather than substituting something else because the internet suggested it.

The other thing worth reading

Check the serving size before you compare anything at all. A product boasting big numbers per serving may define a serving as three gummies or four capsules. Divide everything by the serving size and the comparison usually looks different.

And be wary of proprietary blends, where several ingredients share a single combined weight. There is only one reason to hide the individual amounts, and it is not to save space on the label.

A quick reference

• Zinc: bisglycinate over oxide
• Magnesium: citrate, glycinate or malate over oxide
• Iron: bisglycinate if sulphate has upset you before
• Vitamin D: cholecalciferol, not ergocalciferol
• Vitamin K: menaquinone if you specifically want K2
• Vitamin E: d-alpha, not dl-alpha
• Vitamin A: retinol is preformed, beta carotene needs converting
• Always divide by the serving size before comparing

You can see every form we use, and the amounts, on the GUUDIES ingredients page. If a brand will not tell you the form, that is information too.