How to Read a Magnesium Label (UK): Elemental vs Compound

Here's a habit that will save you money and confusion: the biggest number on the front of a magnesium tub is usually not the amount of magnesium you're getting. This short guide shows you how to read a UK magnesium label properly — the difference between the compound and the elemental mineral, the one figure that actually counts, and how the % NRV decides what the product is even allowed to claim.

Compound weight vs elemental magnesium

Magnesium is always sold bound to a carrier — an acid or amino acid — because pure magnesium metal isn't something you'd swallow. So "magnesium citrate 1500 mg" means 1500 mg of the whole compound, of which only a fraction is magnesium itself. That fraction is the elemental magnesium, and it's the number that counts toward your daily intake. A good label states it plainly, usually next to a % of the Nutrient Reference Value (NRV). If a label only shows the big compound figure and hides the elemental amount, that's a reason to be cautious.

The chart shows why two "1500 mg" products can be worlds apart: oxide is mostly magnesium by weight, while gentle chelates like glycinate or L-threonate carry far less magnesium per gram — you take them for tolerability, not for a big elemental dose.

The 15% NRV rule — and what it unlocks

In Great Britain, a supplement can only make a magnesium health claim if a serving provides at least 15% of the NRV. The NRV for magnesium is 375 mg, so 15% is about 56 mg of elemental magnesium. Clear that bar and the authorised claims for magnesium apply — it contributes to normal psychological function, the normal functioning of the nervous system, a reduction of tiredness and fatigue, normal muscle function, and the maintenance of normal bones and teeth, among others. Below the bar, no magnesium claim is permitted, however large the compound number looks.

A worked example

Take Humming Herbs' Magnesium L-Threonate: the front says 1500 mg (the compound), and the panel declares 120 mg elemental magnesium = 30% NRV. Because 30% clears the 15% threshold, the authorised magnesium claims apply — and you know exactly how much mineral you're taking, rather than guessing from the headline number. That's what a transparent label looks like.

Your 20-second label checklist

• Is the elemental magnesium stated in mg (not just the compound)?
• Is a % NRV shown, and is it at least 15%?
• Does the form suit you (gentle chelate vs higher-dose oxide/citrate)?
• Are any "benefit" words limited to the authorised magnesium claims — not form-specific promises?

Where to go next

Now that you can read the panel, the natural next step is choosing a form. Our companion guide, Magnesium in the UK: the forms explained & how to choose, walks through oxide, citrate, glycinate and the rest. And if you're specifically weighing up the newest chelate, see the magnesium L-threonate guide.

References

• Great Britain Nutrition and Health Claims (NHC) Register — authorised claims for magnesium: gov.uk/…/great-britain-nutrition-and-health-claims-nhc-register
• Retained EU law — Nutrient Reference Values (Annex): legislation.gov.uk/eur/2011/1169
• NHS — Vitamins and minerals: Others (including magnesium): nhs.uk/conditions/vitamins-and-minerals/others

This article is for general information and is not medical advice. Food supplements should not replace a varied, balanced diet or a healthy lifestyle. If you are pregnant, breastfeeding, taking medication or under medical care, speak to a qualified health professional before use. Do not exceed the stated dose.