How to read a Supplement Facts label

1. Serving size and servings per container

Every amount on the panel is per serving, and a serving can be one capsule or four. Two products that both print "1,000 mg" can differ fourfold once you check how many units make the serving. The directions, outside the panel, say how many servings a day the maker suggests; 97% of products in the database carry a directions statement. PlainVitamins shows each amount per serving and, where the directions give a number, per day at the most servings allowed.

2. Amount per serving

Each row names an ingredient and its amount, in a unit that depends on the nutrient: milligrams, micrograms, micrograms DFE for folate (dietary folate equivalents), micrograms RAE for vitamin A, IU on older labels. Amounts in different units cannot be compared directly; vitamin D is the exception that converts exactly, at 40 IU per microgram. The typical product lists 5 rows; 31% list a single ingredient.

3. % Daily Value

The %DV compares the amount with the FDA Daily Value, a labelling reference for adults and children 4 and older. It is printed for nutrients that have a Daily Value; ingredients without one (most botanicals, for example) carry a dagger and the note "Daily Value not established". A %DV above 100 is common and lawful. What the DV is, and how it differs from the upper limit, is the next guide.

4. Proprietary blends

A blend lists several ingredients under one name with only the blend's total weight. FDA rules allow it, with the ingredients in descending order by weight, but the amount of each one inside is not disclosed. 29% of products in the database have at least one ingredient whose amount is hidden this way. A product page marks those rows "not disclosed".

5. Other ingredients

Below the panel, "Other ingredients" lists what is not a dietary ingredient: the capsule shell, fillers, binders, flow agents, colours and flavours. The typical label lists 4. Allergens can appear here, so read it if you avoid one.

6. The statements around the panel

• Warnings. 91% of products print at least one precaution; 81% warn about children and 66% about pregnancy, nursing or prescription medicines.
• The FDA disclaimer. A label that makes a claim about the body's structure or function must say the FDA has not evaluated it; 76% of products carry it.
• Seals and symbols. 53% print a seal or symbol of some kind, from organic and vegan marks to testing programmes. A seal is the label's claim; the seals analysis links each certifier's own list.

Check a label against the market

Look a product up on PlainVitamins: its page shows each row of its label, where the amount sits among every product listing the same ingredient, and the Daily Value and adult upper limit beside it. The data is NIH's transcription (version 9.4.0); the bottle in your hand is the authority on what it says today.