Multivitamin supplements: who benefits, who does not, and what to check on the label

The term has no legal definition for strength or content. Products range from low-dose daily tablets to high-potency formulas with many times the daily reference amounts. Some add minerals such as zinc, iron or selenium, and some include herbal extracts. In the UK they are food supplements, not licensed medicines, so they are not assessed for treating disease.

NCCIH summarises mixed results from research. Taking a basic daily multivitamin and mineral product is unlikely to pose a risk for healthy people, but most studies have found little link between taking one and preventing disease. It therefore makes sense to treat a multivitamin as insurance for gaps rather than as a health intervention. MedlinePlus likewise says the best way to get enough vitamins is a balanced diet and that supplements may be needed in some cases.

The British Nutrition Foundation and the NHS summarise the national recommendations. Children from 6 months to 5 years are advised to have vitamins A, C and D as drops unless they take enough infant formula. Everyone over 5 is encouraged to consider vitamin D in autumn and winter, and all year for people with little sun exposure or darker skin. Women who are pregnant or could conceive should take folic acid, 400 micrograms daily until week 12 of pregnancy, with a higher dose prescribed for higher-risk cases.

A general multivitamin may cover some of these needs, but not always at the recommended amount, which is why a targeted product is often better than a broad one.

• Folic acid and vitamin D are the nutrients where a specific, labelled dose matters most.

• Check the vitamin D content in micrograms before assuming a multivitamin counts.

• For children under 5, the Healthy Start-style drops are designed for the age group.

People with coeliac disease, inflammatory bowel disease, cystic fibrosis, bariatric surgery, dialysis, restricted diets, or alcohol dependence may be advised to take a supplement by a doctor or dietitian. Older adults with poor appetite or people recovering from illness may also benefit. In these situations the product and doses should be tailored, and blood tests may guide the choice.

Three nutrients deserve particular attention. Vitamin A (retinol) is best avoided in pregnancy and limited with regular liver intake. Vitamin B6 is advised by the NHS at no more than 10mg a day in supplements unless a doctor says otherwise. Iron can be dangerous in overdose, and NCCIH specifically notes that iron supplements are a poisoning risk for young children, so products should be stored out of reach.

Add up everything you take. Combining a multivitamin, a cod liver oil capsule, a hair-and-nails tablet and a fortified drink can push fat-soluble vitamins and B6 above sensible levels without any single product looking excessive. MedlinePlus advises not to exceed 100 percent of the recommended amounts without medical supervision, particularly for fat-soluble vitamins that accumulate.

Tell your pharmacist or prescriber about supplements, especially if you take warfarin, thyroid hormone, antibiotics such as tetracyclines or quinolones, or medicines for epilepsy or cancer. Minerals can bind some drugs in the gut, vitamin K affects warfarin, and biotin can distort blood tests. Mention supplements before surgery too.