Do I need a multivitamin? Who benefits, what the big trials found and how to choose the best multivitamin in the UK

Do I need a multivitamin?

If you’re healthy and eat a varied diet, you probably don’t. A multivitamin won’t replace food or protect you from disease. But sometimes it fills real gaps:

• your diet is limited, you eat very little or you’re on a strict diet;
• you’re vegan and don’t eat fortified foods;
• you’re over 50, when B12 from food is absorbed less well;
• you could get pregnant or are planning to, so you need folic acid;
• your doctor has told you that you don’t absorb nutrients well.

Not sure where to start? Our quick vitamin check shows whether you need a multivitamin or just one or two single supplements.

Multivitamin benefits: what the large trials found

Multivitamins have been tested in tens of thousands of people, and the result is sobering: no clear protection against the major diseases.

The COSMOS memory results are interesting, but the effect was small and the people were older. They’re no reason to take a multivitamin “for your brain” at 30. Figures are taken from the NIH ODS review.

Who might benefit from a multivitamin

NIH ODS lists several groups that may gain from one:

• women who could get pregnant, for the folic acid. The dose matters, though – see our folic acid guide;
• people over 50, for vitamin B12, which is absorbed better from supplements than from food;
• vegans and strict vegetarians, for B12 and sometimes iron, zinc, iodine and vitamin D;
• people with conditions that affect absorption, on medical advice.

If your gap is one nutrient, a single supplement is usually more precise. Vegans need a B12 supplement first, and in the UK the NHS advises vitamin D for everyone in autumn and winter.

If you do want a multivitamin, the right formula depends on who you are. Pick the option that fits:

Who doesn’t need one, or needs a different product

• If you have a confirmed deficiency. Multivitamin doses are for prevention, and low iron, B12 or vitamin D is treated separately.
• If you’re pregnant: a standard multivitamin may contain retinol. You need a pregnancy formula; see our guide to pregnancy vitamins.
• If your bathroom cabinet already holds three or four single supplements. A multivitamin on top tends to cause overlap rather than benefit.
• Children. Adult formulas aren’t suitable. Children’s doses depend on age and weight, so follow the label and your GP or health visitor.

What to look for: doses vs NRV

UK and EU labels show the share of the NRV (nutrient reference value for adults). US bottles on iHerb show % DV, a similar figure based on US values. A good everyday multivitamin gives about 100% of the reference for most vitamins. More isn’t better without a reason.

Calcium and magnesium are almost always low in a one-a-day tablet, because the full amount simply won’t fit. If you need them, count them separately. Tap the lines of a typical label below to see what to check.

Iron, vitamin A and beta-carotene: three common traps

Iron. Men and women over 50 need 8.7 mg of iron a day; women aged 19–50 need 14.8 mg (Food Standards Scotland). Your body has almost no way to get rid of excess iron. So men and post-menopausal women without a deficiency should choose an iron-free formula. If you do need iron, our guide to iron tablets compares the forms.

Vitamin A (retinol). The NHS warns that more than an average of 1.5 mg (1,500 mcg) of vitamin A a day over many years may affect your bones. In pregnancy, too much preformed vitamin A can cause birth defects. On the label, retinol appears as retinyl palmitate or retinyl acetate.

Beta-carotene. This plant form of vitamin A doesn’t carry the bone and pregnancy risks of retinol. But if you smoke, avoid it in supplements. In two large trials in smokers (one also included people exposed to asbestos), 20–30 mg of beta-carotene a day raised lung cancer risk by 18% and 28%. One of the trials added retinol. EFSA says smokers should avoid supplements containing beta-carotene. The NHS says the same for anyone exposed to asbestos, and advises everyone else to take no more than 7 mg a day from supplements unless a doctor suggests more.

What this means when you choose:

• if you don’t smoke and aren’t planning a pregnancy, a mix of retinol and beta-carotene is fine;
• in pregnancy, choose a formula with no retinol;
• if you smoke or used to, pick a formula without beta-carotene, or with little vitamin A.

Multivitamin gummies

Gummies suit people who struggle to swallow tablets. But they have their downsides:

• they often contain fewer minerals – iron, zinc, calcium and magnesium may be missing altogether;
• a serving usually contains sugar or sugar alcohols – check the Total Sugars line;
• a serving is often 2–3 gummies, and the label doses refer to that serving;
• they look like sweets, so keep the jar out of children’s reach.

If you mainly want vitamins D and B12, gummies are fine. If you need minerals, compare the label with a tablet.

Multivitamins and medicines: when to ask your GP

• Levothyroxine. The NHS lists calcium and iron supplements among the products that affect it. A gap of at least 4 hours is the usual advice; check with your pharmacist.
• Warfarin. Vitamin K affects clotting. Don’t start or stop a multivitamin without advice.
• With kidney disease, take magnesium, potassium and vitamins A and D only on medical advice.
• In pregnancy and breastfeeding the formula and doses are different, so agree them with your midwife or GP.
• If you take several supplements at once, check the pairs in our vitamin compatibility chart.

How to choose the best multivitamin on iHerb

1. Decide whether you need a multivitamin at all, or just one supplement (B12, vitamin D, folic acid).
2. Choose a formula that fits you: men’s or women’s, under or over 50. See supplements for women and supplements for men for the details.
3. Compare doses with the table above: about 100% NRV, B6 no more than 10 mg, vitamin D 10–25 mcg.
4. Men and post-menopause: iron-free. Smokers: no beta-carotene. Pregnancy: no retinol.
5. Add up the doses across all your bottles, especially vitamin D, zinc, iron and B6.
6. Look for independent quality marks (USP, NSF or similar).

How to read Supplement Facts and tell % DV from NRV is covered in our guide to supplement labels.