Supplement glossary

Supplement labels are full of chemistry shorthand — L-this, chelated that, 10:1 extracts, IU vs. mg. Most of it is understandable in a sentence or two. This glossary explains the terms you will meet most often in the SuppSafety library and on real labels. Informational only; none of this is a recommendation for any particular form or product.

Chemical form prefixes

L- and D- forms (stereochemistry)

Many molecules exist in mirror-image versions, like left and right hands; chemists label them with prefixes such as L- and D-. The letters do not mean “left is better” — they identify which mirror image is in the bottle, because biology often uses one form and not the other. L-theanine and L-carnitine, for example, name the biologically relevant form. When a label says “DL-”, it is a mix of both.

“HCl” and other salt forms

“HCl” after a name (as in betaine HCl) means the compound is bound to hydrochloride as a salt — a common way to make an ingredient stable and easier to formulate. Salt forms change the weight of a dose: part of each milligram is the salt, not the active molecule (see “elemental vs. compound dose” below).

Amino acid forms

Many supplements are amino acids or built from them. Free-form amino acids (like L-glycine or L-taurine) are single amino acids sold on their own; “bound” or peptide forms link several together, as in collagen peptides or protein powders. The L- prefix again just names the naturally occurring mirror-image form. Amino acids are often discussed around timing with or without food, since a large protein meal provides many of them at once.

Mineral forms

Chelated minerals

A chelated mineral is bound to another molecule — often an amino acid like glycine — that carries it through digestion. Chelates such as magnesium glycinate are commonly discussed as gentler on the stomach; whether they are meaningfully better absorbed varies by mineral and by study.

Oxide vs. glycinate vs. citrate vs. threonate

Using magnesium as the example: oxide packs the most elemental magnesium per pill but is commonly reported to cause loose stools and is often discussed as less well absorbed; citrate is a middle ground; glycinate is the common “gentle” chelate; and threonate is a newer, more expensive form with its own early-stage research. Compare magnesium glycinate, magnesium citrate, and magnesium L-threonate in the library.

Vitamin forms

Methylated vitamins (methylfolate, methylcobalamin)

“Methylated” B vitamins carry a methyl group the body would otherwise add itself — methylfolate instead of folic acid, methylcobalamin instead of cyanocobalamin. They are commonly discussed in the context of genetic variants that affect folate metabolism. Whether the methylated form matters for a given person is an individual question worth raising with a professional, not a general upgrade.

MK-4 vs. MK-7 (vitamin K2)

These are two sub-forms of vitamin K2 with different lifetimes in the body: MK-7 stays around much longer per dose, while MK-4 is shorter acting and was used in some higher-dose research. Labels and studies are form-specific, so it is worth knowing which one you are looking at. See vitamin K2 (MK-7) and MK-4.

EPA and DHA

The two main omega-3 fatty acids in fish oil. A “1000 mg fish oil” softgel may contain only 300–600 mg of actual EPA+DHA — the combined EPA/DHA number on the back label is the one people usually compare.

Extracts and standardization

Extract ratios (e.g., 10:1)

A 10:1 extract means roughly ten grams of raw plant material were concentrated into one gram of extract. The ratio says how concentrated the material is — not how much of any specific active compound it contains. Two 10:1 extracts of the same herb can differ substantially.

Standardized extracts

A standardized extract is adjusted so each batch contains a stated amount of a marker compound — for example, an ashwagandha extract standardized to a percentage of withanolides. Standardization makes doses comparable between batches and closer to what studies used, which is why it is commonly looked for on botanical labels.

Doses and units

IU vs. mg and mcg

IU (international units) is a biological-activity unit still used for vitamins A, D, and E; mg and mcg are simple weight. Conversions are vitamin-specific — for vitamin D, 400 IU equals 10 mcg. Newer labels often show both.

Elemental vs. compound dose

Minerals are sold as compounds, and only part of the compound's weight is the mineral itself. “Magnesium glycinate 1000 mg” might provide around 100 mg of elemental magnesium. The elemental number — usually in the Supplement Facts panel — is the one that matters for comparing doses.

Contaminants & heavy metals

Where heavy metals come up

Some supplement categories are more commonly discussed around heavy metals (such as lead, arsenic, cadmium, and mercury) because of where the raw material comes from:

• Botanicals and greens can take up metals from soil; concentrated extracts (for example green tea extract or turmeric) are commonly discussed for both potency variation and contaminants.
• Minerals and trace-mineral products are mined or sea-sourced, so quality varies; kelp-derived iodine in particular is commonly noted for both variable iodine content and possible arsenic.
• Protein powders and collagen have had public heavy-metal testing discussions; a certificate of analysis is commonly recommended for collagen peptides.
• Cacao is commonly discussed around cadmium and lead, which is why third-party testing is often looked for on cacao products.

This is general context, not a claim about any specific product. Third-party testing and a batch COA are the usual ways people check.

Quality and testing terms

“Organic” vs. third-party tested — different claims

“Organic” describes how an ingredient was grown; third-party testing describes whether a finished product was checked — for identity, potency, or contaminants. Neither implies the other: an organic botanical can still carry heavy metals from soil, and a tested product need not be organic. Our organic vs. synthetic guide goes deeper.

COA (certificate of analysis)

A lab document for a specific batch reporting what was tested — identity, potency, and often contaminants such as heavy metals or microbes. Some brands publish COAs or provide them on request. A COA is only as good as the lab behind it, but asking for one is a reasonable quality habit.

Third-party testing marks

Independent organizations — USP, NSF, and Informed Choice are common examples — verify that a product contains what the label says and check for certain contaminants. Their marks are about label accuracy and purity, not about whether the supplement works or is right for you. The quality guide explains how to weigh these marks.

See these terms in context: browse the library → or build your stack →