How to read a supplement label: NRV, forms and blends

Supplement labels are written for regulators, not people. Once you know five things, you can read any of them in a couple of minutes.

1. The daily portion

Every number on the panel refers to a "recommended daily portion". It might be one scoop, two capsules or three. Check this first, or every comparison you make will be off.

2. What %NRV means, and what it doesn't

NRV stands for nutrient reference value: a fixed adult reference used on UK and EU labels.¹ The %NRV is simply: amount ÷ NRV × 100.

• Magnesium 100 mg ÷ 375 mg = 27% NRV
• Vitamin D 10 µg ÷ 5 µg = 200% NRV

Three things it isn't:

• Your personal requirement. That depends on your diet, age and health.
• A target. 100% isn't "optimal"; 1,000% isn't ten times the benefit.
• A safety limit. Upper limits are separate. Vitamin B6's NRV is 1.4 mg, and its European upper level is 12 mg.²

A UK quirk: the label NRV for vitamin D is 5 µg, but NHS advice is 10 µg a day for many people, especially in autumn and winter.³ Both numbers are correct; they answer different questions.

Watch for US labels. "%DV" is the American system, with different reference amounts. It isn't %NRV.

3. Forms: important, but no miracles

• Vitamin D3 vs D2: D3 generally raises blood vitamin D more effectively, especially in larger, less frequent doses.⁴
• Magnesium: what matters is the elemental magnesium, not the weight of the salt it's bound to. Some salts are better absorbed than magnesium oxide in small studies; that doesn't make every "glycinate" clinically superior.⁵
• Folate: methylfolate skips one conversion step. That doesn't mean folic acid doesn't work. NHS pregnancy advice specifically uses folic acid.⁶
• "Methylated", "bioactive", "chelated", "natural": useful descriptions, not proof of better results.

4. Blends that hide doses

"Proprietary blend, 1,500 mg" followed by a list of 15 herbs tells you the total, not how much of each. The first ingredient might be most of it. In the UK, supplements must declare the quantity of each substance with a nutritional or physiological effect, per daily portion.⁷ A brand name doesn't change that.

For botanicals, look for the plant part, extract and standardisation, for example "saffron stigma extract, standardised to crocins".

5. What must be on a UK pack

• The words "food supplement"
• The daily portion, and a warning not to exceed it
• A statement that supplements shouldn't replace a varied diet
• "Store out of reach of young children"
• Amounts of nutrients and active substances, with %NRV for vitamins and minerals
• Ingredients with allergens emphasised, net quantity, date mark and the responsible business⁷⁻⁸

If you're buying online, this information should be available before you pay.⁸

A two-minute checklist

Daily portion → every amount listed → elemental minerals → %NRV, not %DV → total across everything you take vs upper limits → extract details for botanicals.