How to read a supplement label, line by line

Start with the serving size

Every number on a supplement label refers to a set amount of product. Under EU law, the label must state the portion recommended for daily consumption, with a warning not to exceed it¹. The nutrient amounts are then given for that daily portion¹.

US labels call this the serving size. The US Food and Drug Administration (FDA) defines one serving as the most the label recommends per eating occasion. If there is no recommendation, a serving is one unit, such as one capsule².

So read the serving line first. If a serving is two capsules, every amount on the panel is for two capsules, not one.

Amount per serving, %NRV and %DV

The amount column shows how much of each nutrient one serving provides. EU law requires these amounts as numbers, in set units such as milligrams (mg) or micrograms (µg)¹. US labels write micrograms as mcg³.

Next to each amount there is usually a percentage. EU law requires vitamins and minerals to be shown as a percentage of reference values as well¹. These are the nutrient reference values (NRVs) in Annex XIII of Regulation (EU) No 1169/2011, which lists 13 vitamins and 14 minerals^{4, 5}. US labels show %DV instead: the share of FDA's Daily Value³.

The two systems use different reference numbers, so the same product can show very different percentages:

• Vitamin D: the NRV is 5 µg⁵ and the US Daily Value is 20 µg³. A serving with 10 µg is 200% NRV but 50% DV.
• Vitamin B12: the NRV is 2.5 µg⁵ and the Daily Value is 2.4 µg³.
• Vitamin A: the NRV is 800 µg⁵ and the Daily Value is 900 µg RAE³.

A percentage is a comparison with a reference value set for labelling. It does not tell you whether that amount suits you.

When there is no NRV

Annex XIII only covers those vitamins and minerals⁵. Many supplement ingredients are not on the list, for example the omega-3 fats EPA and DHA⁶. With no reference value, there is no percentage to show.

US rules handle this with a symbol in the %DV column that points to the footnote "Daily Value not established"². When a label says "NRV not established", or shows a symbol in the %NRV column, it means the same thing. There is no official reference value to compare against. It is not a warning, and it does not mean the ingredient is missing.

The compound is not the nutrient

Vitamins and minerals are added in specific chemical forms. EU law lists the forms allowed in food supplements¹. These include:

• Vitamin A: retinol, retinyl acetate, retinyl palmitate or beta-carotene.
• Vitamin D: cholecalciferol or ergocalciferol, also known as vitamin D3 and vitamin D2⁷.
• Vitamin B12: cyanocobalamin or hydroxocobalamin.

Cyanocobalamin is the most common form of vitamin B12 in supplements. The body converts it into the active forms, methylcobalamin and 5-deoxyadenosylcobalamin⁸.

A compound weighs more than the nutrient it supplies. Calcium carbonate is 40% calcium by weight, and calcium citrate is 21% calcium⁹. FDA tells manufacturers to list the weight of the calcium, not the weight of the calcium carbonate². So the ingredient list may name the compound, while the panel shows the nutrient.

Vitamin A follows a similar idea. Labels declare it in µg RAE, or retinol activity equivalents, a unit that accounts for the different activity of each form¹⁰.

You may also see international units (IU). The conversions are fixed:

• Vitamin D: 1 µg equals 40 IU⁷.
• Vitamin A as retinol: 1 IU equals 0.3 µg RAE¹⁰.
• Vitamin E: 1 IU equals 0.67 mg of natural alpha-tocopherol, or 0.45 mg of the synthetic form¹¹.

So the same number of IU of vitamin E can mean a different weight, depending on the form.

Excipients, shells and certificates

Below the panel sits the ingredient list. EU law requires it to include every ingredient, in descending order of weight⁴. An ingredient is any substance used to make the food that is still present in the finished product, including food additives⁴. On that definition, the material of a capsule shell counts too. FDA likewise requires binders, excipients and fillers to appear in the ingredient statement².

Certificates on a pack describe how a product is made:

• GMP (Good Manufacturing Practice): in the US, FDA's GMPs for supplements help ensure identity, purity, strength and composition¹².
• ISO 22000: sets requirements for a food safety management system. It applies to organisations across the food chain and includes HACCP principles¹³.
• FSSC 22000: a certification scheme built on ISO 22000, sector prerequisite programmes and its own added requirements. The Global Food Safety Initiative recognises it¹⁴.

All three concern the manufacturer's processes. None of them is a test of whether a product has a health effect. The US Office of Dietary Supplements makes a similar point about independent quality seals: they do not guarantee that a product is safe or effective¹².

This article is general information, not medical advice. Talk to your doctor or pharmacist before starting a supplement, especially if you are pregnant, breastfeeding, taking medicines or managing a health condition.