A supplement label answers three questions: how much of each nutrient is in one daily dose, how that amount compares with a standard reference value, and how much of the product you are meant to take. Once you can read those three things, comparing two tubs on a shelf or two product pages becomes much easier.
This guide explains the units and abbreviations you will see, the amounts the NHS gives for adults for three common supplements, and what the compulsory warnings on the pack mean. It is general information about labels, not advice on whether you need a supplement. Most people can get what they need from a varied diet, and your doctor or pharmacist is the right person to ask about your own situation, especially if you take medicines, are pregnant or have a health condition.
What has to be on the label
Under the food supplements rules used in the UK and the EU, every supplement label must show:
- the names of the nutrients or substances that characterise the product;
- the recommended daily portion, for example “one capsule a day”;
- a warning not to exceed the stated recommended daily dose;
- a statement that food supplements should not be used as a substitute for a varied diet;
- a statement that the product should be stored out of the reach of young children.
The same rules say a supplement label must not claim that the product prevents, treats or cures a disease. If a product page promises to cure something, treat that as a warning sign.
Units: mg, µg and IU
Vitamins and minerals are listed by weight, and the amounts are small:
| Unit | Meaning | Typical use |
|---|---|---|
| mg | milligram, one thousandth of a gram | Magnesium, iron, vitamin C, vitamin E |
| µg or mcg | microgram, one thousandth of a milligram | Vitamin D, vitamin K, selenium, vitamin B12 |
| IU | international unit, a measure of activity | Vitamin D, sometimes vitamin E |
For vitamin D, the NHS gives the conversion: 1 microgram equals 40 IU. So 10 µg is 400 IU, 25 µg is 1,000 IU and 75 µg is 3,000 IU. Convert IU to micrograms before comparing with NHS guidance.
What NRV means
Next to each amount you will usually see a percentage marked “% NRV”. NRV stands for nutrient reference value. It is a fixed figure set in labelling law so that products can be compared on the same basis. It is not a personal target and it is not the same as the amount the NHS recommends for you.
Some adult NRVs from the UK labelling rules:
| Nutrient | NRV |
|---|---|
| Vitamin D | 5 µg |
| Vitamin C | 80 mg |
| Vitamin E | 12 mg |
| Vitamin K | 75 µg |
| Magnesium | 375 mg |
| Iron | 14 mg |
| Selenium | 55 µg |
A vitamin D product with 25 µg per dose therefore shows 500% NRV. A high percentage does not automatically mean a product is better or worse; it simply tells you how far above the reference value one dose is. What matters more is how the amount compares with the guidance for your age and situation and with the safe upper amounts.
Vitamin D, iron and magnesium: the NHS figures
The NHS publishes daily amounts for adults and, for many nutrients, an amount from supplements that is unlikely to cause harm.
Vitamin D. Adults need 10 µg a day. The NHS says everyone should consider a daily 10 µg supplement in autumn and winter, roughly October to early March, because sunlight is not strong enough for the body to make vitamin D then. Some groups are advised to consider one all year, including people who are rarely outdoors and people with dark skin. The NHS gives 100 µg (4,000 IU) a day as the upper amount for adults. You can compare capsules, drops and sprays in the vitamin D range.
Iron. Men aged 19 and over need 8.7 mg a day and women aged 19 to 49 need 14.8 mg a day. The NHS says 17 mg or less a day from supplements is unlikely to cause harm, and that higher doses should only be taken on a GP’s advice. Doses above 20 mg can cause constipation, nausea and stomach pain. Iron supplements must be kept away from children, because very high doses can be fatal for them.
Magnesium. Adults aged 19 to 64 need around 300 mg a day for men and 270 mg a day for women. The NHS says 400 mg or less a day from supplements is unlikely to cause harm. The magnesium range on this site also includes bath flakes, sprays and lotions, which are not the same as tablets: read the product type before you compare.
Remember that these amounts include what you already get from food, and that several products can contain the same nutrient. A multivitamin plus a separate vitamin D spray plus a fortified drink can add up.
Comparing two products
When two products look similar, work through the label in this order:
- Amount per daily dose. Some products need two or three capsules a day to reach the amount shown, so check whether the figure is per capsule or per dose.
- Form of the nutrient. Magnesium may be listed as citrate, glycinate, oxide or malate; iron as fumarate, sulphate or bisglycinate. The form changes how much of the elemental mineral each capsule delivers, and labels usually state the elemental amount in the nutrition table.
- Price per daily dose. Divide the price by the number of daily doses in the pack, not the number of capsules.
- Other ingredients. Check capsule shells (gelatine or vegetable), allergens and any added herbs or stimulants.
- Format. Capsules, tablets, sprays, drops and gummies suit different people, but gummies often contain sugar.
The wider vitamins and minerals range lets you compare several brands side by side, and the product pages link through to the shops, where you can read the full label before you order.
Quick checklist
- Find the amount per daily dose, not per capsule.
- Convert IU to micrograms for vitamin D (divide by 40).
- Treat % NRV as a comparison figure, not a personal target.
- Compare the dose with NHS amounts and upper limits.
- Add up the same nutrient across all products you take.
- Check the form, the other ingredients and the price per day.
- Keep all supplements, especially iron, out of children’s reach.
- Ask a pharmacist or doctor if you take medicines or have a condition.
If you are building a home training routine at the same time, the guide to dumbbells, kettlebells and resistance bands covers the equipment side.
Common questions
Is a higher % NRV better?
Not necessarily. NRV is a fixed reference figure for labels. A dose far above it is not more useful if you already get enough, and for some nutrients there are upper amounts you should stay under. Compare the dose with NHS guidance and ask a pharmacist if unsure.
How many IU is 10 micrograms of vitamin D?
10 µg is 400 IU, because the NHS gives 1 µg as 40 IU. A product labelled 1,000 IU contains 25 µg per dose.
Can I take several supplements together?
Some combinations are fine and some add up to more than you need or interact with medicines. List everything you take, including multivitamins and fortified foods, and check the total with a pharmacist or doctor.
