In short
- The nutrient and the compound it comes in are two different things; labels list both.
- Different compounds contain different shares of the actual nutrient, so milligrams of compound and milligrams of mineral are not the same.
- Names such as "citrate", "oxide" and "bisglycinate" describe what the nutrient is bound to.
- The right form depends on your diet, your preferences and what you and your clinician decide, not on which name sounds most advanced.
Read enough supplement labels and a pattern appears: the nutrient you are looking for is followed by a word in parentheses. "Magnesium (as magnesium citrate)." "Calcium (as calcium carbonate)." "Vitamin B12 (as methylcobalamin)." That parenthetical tells you which form of the nutrient is in the product. It is one of the most useful pieces of information on the label, and one of the least explained.
Why forms exist at all
Minerals cannot be sold as pure metal. Magnesium, calcium and zinc all have to be bound to something else, such as an acid or an amino acid, to be stable, to be swallowed, or to taste acceptable. Vitamins can exist in more than one chemical shape, and manufacturers pick the version that is stable on a shelf, widely available and reasonably priced. The result is a long list of names that mean little until someone translates them.
Elemental amount versus compound weight
The key idea is the difference between the elemental amount (how much actual magnesium, calcium or zinc is present) and the weight of the compound (the total mass including everything it is bound to). By regulation the Supplement Facts panel states the elemental amount for most minerals, and that is the number to compare. But a product description or a front-of-bottle claim may quote the compound weight, which is larger.
Different compounds carry different shares of the mineral. Some well-known examples:
| Compound | Approximate share that is the mineral |
|---|---|
| Calcium carbonate | About 40% calcium |
| Calcium citrate | About 21% calcium |
| Magnesium oxide | About 60% magnesium |
| Magnesium citrate | About 16% magnesium |
| Magnesium glycinate (bisglycinate) | About 14% magnesium |
This is why a "1,000 mg magnesium oxide" tablet and a "1,000 mg magnesium glycinate" tablet contain very different amounts of magnesium. It also explains why you should always check the elemental line on the panel and not the headline on the front.
Common mineral forms
Carbonate and oxide
Carbonates and oxides are inexpensive, compact and carry a high share of the mineral, which is why they are common in single-tablet products. They generally dissolve best in the presence of stomach acid, so many manufacturers suggest taking calcium carbonate with a meal.
Citrate, gluconate, lactate and malate
These pair the mineral with an organic acid. Citrate forms are popular for calcium and magnesium because they do not depend as heavily on stomach acid. They carry a lower share of the mineral per milligram of compound, so the tablet or capsule is often larger, or you take more of them for the same amount.
Chelates and bisglycinates
A chelate is a mineral bound to one or more amino acids. "Bisglycinate" means the mineral is bound to two glycine molecules. The pitch is that chelates are gentle on the stomach, and many people choose them for that reason. Before paying more, read the elemental amount on the panel: gentle forms often contain less mineral per capsule, so the comparison depends on how many capsules you would need to take.
Sulfates and picolinates
Zinc sulfate and iron sulfate (ferrous sulfate) are long-established forms. Picolinate pairs a mineral such as zinc or chromium with picolinic acid. As with other forms, the label gives the elemental amount; the name tells you what it is attached to.
Common vitamin forms
- Vitamin D: D2 (ergocalciferol) and D3 (cholecalciferol). Both are sold as supplements; D3 is the form most products use today.
- Vitamin B12: cyanocobalamin and methylcobalamin are the two most common. Cyanocobalamin is the most stable and widely used; methylcobalamin is often marketed as a "ready-to-use" form.
- Folate: folic acid is the synthetic form; "folate" or "methylfolate" is used for forms closer to what is found in food. On labels it is expressed in DFE (dietary folate equivalents) because the two behave differently in the body.
- Vitamin E: natural vitamin E is written d-alpha-tocopherol; the synthetic version is dl-alpha-tocopherol. "Mixed tocopherols" contain several related compounds.
- Vitamin K: K1 (phylloquinone) and K2 (menaquinones, written MK-4, MK-7 and so on).
- Vitamin C: ascorbic acid is the standard form; buffered forms such as calcium ascorbate or sodium ascorbate are sold for people who prefer a gentler product.
"Natural" and "synthetic" are not the whole story
Labels sometimes sort forms into "natural" and "synthetic" and imply that one is better. The reality is more mixed. Some natural forms are more expensive and less stable; some synthetic forms are chemically identical to what is found in food. If a product claims to be "whole food" or "food-based", check the panel: the amounts and forms listed there are what you are getting, whatever the marketing line says.
How to choose
There is no single best form. A practical way to decide is to ask three questions:
- What is my reason for picking this nutrient? If a clinician has recommended a specific amount and form, follow that and not a general article.
- What suits my stomach and my routine? Some forms are easier to take on an empty stomach; others do better with a meal. The label's "suggested use" tells you what the manufacturer recommends.
- What is the cost per elemental milligram? A cheap bottle of a low-share compound can cost more per useful milligram than a pricier-looking bottle with a higher share. Our worked example shows how to do that sum.
Browse by nutrient
If you are browsing the shop with forms in mind, start with the nutrient sections in Vitamins & Minerals, such as Calcium, Magnesium and Multivitamins, and open each product to read the compound named on its label.