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Last updated: September 2026 · 10 minute read

First, what "contributes to normal" means

Every claim below uses the same shape: the nutrient contributes to normal something. That is not hedging. It is the legal boundary between a food and a medicine. A supplement can say a nutrient is needed for a function that already works. It cannot say the nutrient improves that function, fixes a problem, or treats a condition. When a product page says "boosts", "supports healthy", "helps with" or names a symptom, it has stepped over that line, whatever the ingredient.

On this page the wording in bold is the register's. The explanation beside it is ours, and it only explains; it never adds.

1. Magnesium

Magnesium is a cofactor for more than 300 enzymes, most of them involved in releasing energy from food, building protein and moving ions across cell membranes. It is also one of the minerals UK diets most often fall short on, because it comes from green vegetables, nuts, seeds, pulses and whole grains, which is exactly what processed diets lack.

What magnesium supports: the authorised claims

The form matters more than the milligrams

"Magnesium 500mg" on a label usually means the weight of the compound, not the magnesium. Magnesium glycinate is about 13 to 14% magnesium as a true chelate; magnesium oxide is 60% magnesium but poorly absorbed and laxative at useful doses. Glycinate, magnesium bound to the amino acid glycine, is the form chosen for tolerability, and a page that declares both the compound and the elemental magnesium is telling you the truth about the dose.

2. Potassium citrate

Potassium sits inside your cells, sodium sits outside, and the gradient between them is what nerves and muscles run on. The NHS puts an adult's need at 3,500mg a day, and most people don't get there. Potassium citrate is the form found in fruit and vegetables and is milder on the stomach than potassium chloride.

What potassium supports: the authorised claims

The salt maths

Tri-potassium citrate is about 36% potassium, so a 1000mg capsule provides 358mg of potassium, 18% of the reference value. A label claiming "1000mg potassium" from a 1000mg citrate capsule is out by nearly three times. Our full potassium citrate guide covers this in detail.

3. Vitamin D3 and K2

Vitamin D3 is the form your skin makes in summer sunlight and the form the NHS suggests UK adults consider supplementing from October to March, when the sun is too low to make any. Vitamin K2 is paired with it for one reason: D3 increases calcium absorption, and K2 activates the protein that binds calcium into bone. They carry separate claims on the register, and together they cover the calcium story from gut to skeleton.

What vitamin D3 and K2 support: the authorised claims

4. Zinc

Zinc has more authorised claims than almost any other nutrient, 18 in total, because it is a cofactor in hundreds of enzymes, including the ones that copy DNA and drive cell division. The body cannot store it in any real quantity, so it has to come in daily, from meat, shellfish, seeds, nuts and pulses, or a supplement.

What zinc supports: the authorised claims

Two zinc claims men search for

The fertility and testosterone claims are both maintenance claims. When healthy men were made zinc-deficient in a 1996 study, testosterone fell; when men who already had enough zinc took a high dose in 2009, nothing changed. Zinc keeps a normal level normal, which is exactly what the register lets a seller say, and why "testosterone booster" is a phrase no supplement can lawfully use. Our zinc, testosterone and fertility guide goes through the studies.

Choose one zinc product, not both.

Putting them together

None of these replaces a varied diet, and a supplement only fills a gap that is actually there. If you take regular medication or have a medical condition, check with a pharmacist before adding any of them. The potassium list above is the one people most often skip, and the one that matters most.

Frequently asked questions

What does "contributes to normal" mean on a supplement?
It is the wording the UK register requires. It means the nutrient is needed for a function that already works to keep working. It never means improving that function beyond normal, and it never means treating a condition.

Do I need all four of these?
Not necessarily. Magnesium and potassium are the two most commonly under-consumed in UK diets. Vitamin D is the one the NHS suggests everyone consider in autumn and winter. Zinc matters most if your diet is low in meat, shellfish and seeds. A varied diet comes first; supplements fill gaps.

Can I take magnesium, potassium, vitamin D3 K2 and zinc together?
Generally yes, with food, and within the amounts on each pack. Potassium is the exception: read its caution list first if you have kidney problems or take blood pressure medicines. Zinc and magnesium compete slightly for absorption, so a few hours apart is tidier.

Which magnesium form is best?
Glycinate (bisglycinate) is the chelated form and the gentlest on the stomach. Oxide is cheap but poorly absorbed and laxative at useful doses. All permitted forms carry the same claims; the form is a tolerability choice.

Why is vitamin K2 paired with D3?
D3 increases calcium absorption; K2 activates the proteins that bind calcium into bone. The pairing appears on the register as two separate claims, one for each vitamin.

Does potassium lower blood pressure?
No food supplement can claim that. The authorised claim is the maintenance of normal blood pressure. Raised blood pressure is a GP matter.

Does zinc boost testosterone?
No supplement can lawfully claim that. The authorised claim is the maintenance of normal testosterone levels in the blood: zinc keeps a normal level normal.

Capsules, tablets or powder?
Same nutrient, different format. Capsules and tablets are a fixed, taste-free dose. Powder is cheapest per gram and adjustable, but needs milligram scales. Capsules can be made with no fillers; tablets always need binders.

Disclaimer: Food supplements, not medicines. Not intended to diagnose, treat, cure or prevent any disease. All health claims on this page are the authorised Great Britain claims for the named nutrient, in register wording; the explanations describe those claims and do not extend them. Potassium supplements are unsuitable for people with kidney impairment or on ACE inhibitors, ARBs, potassium-sparing diuretics or potassium-containing medicines without medical advice. Vitamin K2 products are unsuitable for people on anticoagulant medicines without medical advice. Keep supplemental zinc under 25mg a day. Not for under 18s, or during pregnancy or breastfeeding without advice. Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. Charge Products is a trading name of Big Idea Services Ltd, Company No. 11645389, Unit 1, 8 Towerfield Road, Towerfield Industrial Estate, Southend-on-Sea, Essex SS3 9QE.