iHerb supplements in the UK and EU: which form to choose and how much to take

iHerb supplements in the UK and EU: where to start

iHerb is an online shop for vitamins, supplements and natural products. It was founded in California in 1996 and ships to the UK and most EU countries from its US warehouses. The catalogue lists tens of thousands of products. One nutrient often comes in five or six forms, at very different doses and prices.

So before you compare brands, settle two things: which form suits you, and how much to take.

Not everyone needs supplements. In the UK and northern Europe they make the most sense in five cases:

• vitamin D, which the NHS advises everyone to consider at 10 mcg (400 IU) a day in autumn and winter, and all year if you rarely get sun on your skin;
• folic acid, 400 mcg a day before conception and until week 12 of pregnancy (NHS);
• vitamin B12 if you’re vegan, and possibly if you’re over 50 or on metformin, when levels can run low;
• omega-3 if oily fish rarely makes it onto your plate;
• magnesium if your diet is short on nuts, beans, lentils and whole grains.

The most popular supplements: what they’re for and which form to choose

The table answers the questions UK and EU shoppers ask most. Doses, interactions and who should avoid each one are in the full guides.

Magnesium glycinate vs citrate

The best type of magnesium depends on how you tolerate it. Glycinate is gentlest on the gut. Citrate is cheaper and dissolves well. Oxide is the cheapest but the most laxative. Read our full comparison of magnesium glycinate vs citrate and other types.

How much vitamin D3 to take

The NHS advises 10 mcg (400 IU) a day in autumn and winter. Many people take 25–50 mcg (1,000–2,000 IU) in winter, which stays under the limit. Take it with a meal that contains some fat.

Many vitamin D3 bottles on iHerb hold 125 mcg (5,000 IU). That is above the 100 mcg (4,000 IU) daily maximum set by EFSA and the NHS. See how much vitamin D3 to take and whether you need K2.

How to choose the best fish oil

The NHS recommends two portions of fish a week, one of them oily. If you eat less, omega-3 can fill the gap. “Fish Oil 1000 mg” is the weight of the oil: a softgel like that holds only about 300 mg of EPA and DHA. Learn how to choose the best fish oil by EPA and DHA.

Melatonin dosage and other sleep supplements

In the UK, melatonin is a prescription-only medicine, so you may not be able to order it to a UK address. In the EU the rules differ by country. Melatonin works mainly for jet lag and a shifted body clock. 0.5–1 mg is usually enough: 5–10 mg tablets don’t work better and more often leave you groggy.

Glycine for sleep and L-theanine are gentler options with smaller effects. Compare them in our sleep supplements guide.

The best form of zinc

Zinc supports immunity, skin and wound healing. EFSA’s upper limit is 25 mg a day from food and supplements combined. So the popular 50 mg bottles aren’t for long-term use. Find out which form of zinc to choose and how much to take.

B complex vs B12

B vitamins won’t give you more energy unless you’re low in them. B12 is essential for vegans and often needed over 50, and folic acid matters before pregnancy. “B-50” and “B-100” complexes contain 50–100 mg of B6. The NHS advises no more than 10 mg a day from supplements. Read about vitamin B12 and the B complex.

Daily need, upper limit and common iHerb doses

Plenty of people grab the best-selling bottle without checking the dose. The chart shows how much of each nutrient you need, where the safe upper limit is and which dose you’ll most often see on iHerb. Switch between nutrients: for some, the common dose sits past the red line.

How much magnesium or zinc is really in a capsule

“Magnesium glycinate 1000 mg” doesn’t mean 1,000 mg of magnesium. A serving like that holds about 140 mg of the mineral itself. Pick a form, enter the compound weight from the product name, and the calculator shows the elemental magnesium or zinc next to the safe upper limit.

How to choose supplements on iHerb: 6 rules

1. Start with the goal, not the brand. Decide what you need and whether you have a reason to take it. Then choose the form.
2. Look at the elemental amount. The Supplement Facts panel shows how much magnesium, zinc or EPA+DHA a serving contains. Our label guide explains how to read it.
3. Check the serving size. “Serving Size” tells you how many capsules make a serving. It is often 2–4, not one.
4. Compare with the upper limit. Use NHS and EFSA figures, especially for vitamin D, zinc, B6, vitamin A and iron. Popular iHerb doses are often above them.
5. Compare cost per day, not per bottle. Divide the price by the number of days the bottle lasts, or use our supplement cost-per-day calculator.
6. Look for independent testing. USP, NSF and, for omega-3, IFOS seals confirm contents and purity.

Popular supplements and what not to combine them with

These are the interactions people ask about most. For pairs of supplements, see our vitamin compatibility chart.

If you take medication, are pregnant or have a long-term condition, speak to your GP or pharmacist before you order. A quick way is to take a photo of your bottles and show it to the pharmacist when you next collect a prescription.

Ordering from iHerb to the UK and EU

iHerb is an established retailer. It sells third-party brands, so check expiry dates, the Supplement Facts panel and testing seals. Our step-by-step answer to is iHerb legit and how to order covers the whole process.

• UK. iHerb includes VAT in its UK prices and says it aims to cover import duty, so most parcels arrive with nothing extra to pay. Couriers and limits are in our iHerb UK delivery and VAT guide.
• EU. iHerb is registered for IOSS, so VAT is collected at checkout on parcels up to €150. Since 1 July 2026 the EU also charges a €3 duty per customs category on small parcels, which iHerb offsets on orders over €10. Read iHerb shipping to Europe and VAT.
• Before you pay. Estimate the total with our iHerb VAT and duty calculator.

Find your way around DozaVita

• Supplements by goal: sleep, immunity, energy, skin, and women’s and men’s health.
• Supplements A–Z: every nutrient we cover, with its key dose.
• Supplement calculators: zinc intake, omega-3 softgels, B6 and cost per day.
• Popular iHerb brands: what the best-known brands sell and what to check on their labels.