Do I need a multivitamin? What the evidence says

Quick answer: Probably not, if you eat a varied diet. The USPSTF found too little evidence that multivitamins prevent heart disease or cancer, and the NHS says most people get what they need from food. The exceptions are specific: folic acid if you could become pregnant, vitamin D (in winter, and daily from 51 in Canada), B12 for vegans and many over-50s, and vitamins for UK under-5s. Check with a pharmacist first if you take warfarin.

In this guide

Do I need a multivitamin? Who this is for, and when to ask a clinician first
Are multivitamins worth it? What the evidence says
Who should take a multivitamin, by age and diet
Can a multivitamin do harm?
What's free, and what guidance says in the US, Canada and UK
Compare: multivitamin guidance by age and life stage
What to do next
Common questions
Sources

Do I need a multivitamin? Who this is for, and when to ask a clinician first

This guide is for adults in the US, Canada and the UK wondering whether a daily multivitamin is worth buying for themselves or their family. It reports what official guidance and the main trials say. It can't tell you what your own body needs.

The short version: if you eat a varied diet, you probably don't need one. The NHS says most people should get all the nutrients they need from a varied and balanced diet, and Health Canada says supplements are not generally required when eating a variety of nutritious foods — with some specific exceptions, covered below.

Talk to a pharmacist, GP, family doctor or primary-care clinician before starting a multivitamin if you:

Take warfarin or another blood thinner. Vitamin K lowers warfarin's effect, and doctors base the dose partly on how much vitamin K you usually get, says the NIH Office of Dietary Supplements.
Are pregnant or trying to conceive — the product matters (see vitamin A below).
Have had weight-loss surgery. NHS bariatric teams such as University Hospitals Sussex say supplements are needed for life, with yearly blood tests, and that standard chewable shop multivitamins are not suitable. Use the regimen your team gives you.
Have symptoms such as unusual tiredness, breathlessness or numbness. These need a doctor's assessment, often with a blood test, rather than a supplement — see the blood tests worth asking for when you're always tired.

Are multivitamins worth it? What the evidence says

For preventing disease in well-nourished adults, the evidence is weak. For filling a specific gap, it's much stronger.

Heart disease and cancer

In 2022 the US Preventive Services Task Force concluded the evidence is insufficient to judge the benefits and harms of multivitamins for preventing cardiovascular disease or cancer in healthy, non-pregnant adults. It went further for two single nutrients: it recommends against beta-carotene and vitamin E supplements for this purpose. The recommendation doesn't apply to people who are pregnant or could become pregnant, children, or anyone with a known deficiency.

The NIH Office of Dietary Supplements reaches a similar view: most studies found multivitamins have little or no effect on cancer, heart disease, osteoporosis or risk of death. Part of the problem is that people who take them tend to eat better already.

Memory and thinking in older adults

The most-cited positive result comes from COSMOS, a large US trial in adults aged 60 and over. A 2024 combined analysis of three COSMOS sub-studies, about 5,200 people, found a daily multivitamin gave a small benefit to overall cognition and memory over about two years — the authors estimated it was equivalent to about two years less cognitive ageing. It measured scores on memory and thinking tests, not dementia, and comes from one trial programme. The NIH says that for people 60 and over a multivitamin "might" help maintain cognitive function.

Where supplements clearly help

Official guidance focuses on targeted nutrients rather than multivitamins: folic acid before and in early pregnancy to lower the risk of neural tube defects, vitamin D where sun is limited, and B12 for people who can't get or absorb enough from food. A multivitamin is one way to get these, but not the only one.

Who should take a multivitamin, by age and diet

Could become pregnant. Health Canada advises a daily multivitamin with 400 micrograms (0.4 mg) of folic acid for all adults and adolescents who could become pregnant. The NHS advises 400 micrograms of folic acid a day while trying and for the first 12 weeks; some people need a higher prescribed dose. The USPSTF advises 400–800 micrograms for anyone planning or capable of pregnancy.
Pregnant. Canada's Dietary Guidelines recommend a multivitamin with folic acid and 16–20 mg of iron. The NHS says not to take cod liver oil or supplements containing vitamin A (retinol) in pregnancy, because too much can harm the baby — so use a pregnancy-specific product.
Over 50. The NIH advises getting B12 from fortified foods or supplements because absorption from food can fall with age. Health Canada advises a 400 IU (10 microgram) vitamin D supplement daily from 51. Products for older adults usually contain more vitamin D and B12 and less iron.
Vegan. The NHS says a B12 supplement may be needed and suggests fortified foods or supplements for vitamin D, iodine, selenium and calcium. Our guide to what to test and what to take on a vegan diet goes into detail.
Restricted or low-calorie diets, or a poor appetite. The NIH lists these as reasons a multivitamin might be considered.
Babies and young children (UK). NHS Best Start in Life recommends daily vitamins A, C and D from 6 months to 5 years, and vitamin D from birth for breastfed babies.

Can a multivitamin do harm?

A basic once-a-day multivitamin is unlikely to harm you, the NIH says. The risks come from high-dose products, stacking several supplements, or the wrong product for your situation.

Doubling up. Multivitamins can push iron, vitamin A, zinc, niacin and folic acid too high if you also take other supplements or fortified foods. The NHS says folic acid above 1 mg a day can mask vitamin B12 deficiency.
Iron. Men and women aged 50 and over need about 8.7 mg a day, compared with 14.8 mg for women aged 19 to 49, according to the NHS. It says 17 mg or less a day from supplements is unlikely to cause harm, but very high doses can be fatal, especially to children — keep iron out of reach. If you're thinking of taking iron, read why to test before taking iron first.
Vitamin A. Beyond pregnancy, the NHS says more than 1.5 mg (1,500 micrograms) a day over many years may affect bones, and advises people past the menopause and older men to stay under this from food and supplements.
Smokers. The NIH says smokers, and perhaps former smokers, should avoid multivitamins with large amounts of beta-carotene or vitamin A, which might increase lung cancer risk.
Warfarin and vitamin K — see the list at the top.

What's free, and what guidance says in the US, Canada and UK

United States

There's no general recommendation for adults to take a multivitamin, and the USPSTF's 2022 statement found insufficient evidence for disease prevention. The NIH Office of Dietary Supplements points to folic acid for anyone who might become pregnant, prenatal vitamins in pregnancy, B12 after 50, and vitamin D for breastfed babies. There's no national free-supplement scheme; supplements are bought over the counter.

Canada

Canada's Dietary Guidelines say supplements are not generally needed with a varied diet, but recommend a daily multivitamin with 400 micrograms of folic acid for anyone who could become pregnant, a multivitamin with iron in pregnancy, and a daily vitamin D source for everyone, with a 400 IU supplement from age 51 (wording updated March 2026). Supplements are bought over the counter.

United Kingdom

The NHS advises folic acid when trying to conceive and through the first 12 weeks, 10 micrograms of vitamin D a day in autumn and winter (see our vitamin D winter guide), and vitamins A, C and D for children aged 6 months to 5 years. Families on the Healthy Start scheme can get free vitamins: tablets with folic acid and vitamins C and D for pregnancy until the baby's first birthday, and drops with vitamins A, C and D for children up to their fourth birthday.

Compare: multivitamin guidance by age and life stage

Group	What official guidance says	Multivitamin needed?
Babies and under-5s	UK: vitamin D from birth if breastfed; vitamins A, C and D from 6 months to 5 years. US and Canada: 400 IU vitamin D for breastfed babies	Only the drops above; children's products use smaller amounts (NIH)
Adults on a varied diet	Nutrients from food (NHS, Health Canada); evidence insufficient for prevention (USPSTF 2022)	Usually not; consider vitamin D in winter
Could become pregnant	Folic acid 400 micrograms daily (all three countries); Canada says as a multivitamin	Folic acid essential; a multivitamin is one way
Pregnant	Folic acid to 12 weeks (UK); multivitamin with folic acid and 16–20 mg iron (Canada); no vitamin A/retinol supplements (NHS)	Pregnancy-specific product only
Over 50	B12 from fortified foods or supplements (NIH); 400 IU vitamin D daily from 51 (Canada)	Optional; targeted B12 and vitamin D may be enough
Vegan	B12 needed; consider vitamin D, iodine, selenium, calcium (NHS)	B12 essential; a vegan multi is one option
After weight-loss surgery	Lifelong supplements and yearly bloods set by the bariatric team	Yes, as prescribed — not a standard shop product
Smokers	Avoid high-dose beta-carotene and vitamin A (NIH); against beta-carotene for prevention (USPSTF)	Check the label if you take one

Guidance checked 20 October 2026.

What to do next

Start with your diet. If you eat a varied diet and none of the groups above fits, the evidence doesn't support a daily multivitamin for prevention.
Cover the specific gaps that apply to you: folic acid if you could become pregnant, vitamin D in winter or from 51 in Canada, B12 if you're vegan or over 50.
Check the label for vitamin A (retinol), beta-carotene, iron and vitamin K, and add up what you take from every product.
Ask a pharmacist first if you take warfarin or other regular medicines, are pregnant, or have had weight-loss surgery.
Feeling unwell or exhausted? See your doctor for tests rather than buying supplements blind.

If a supplement is right for you, a pharmacy or supermarket own-brand product meeting the amounts above is fine.

Common questions

Are multivitamins worth it?

For most well-fed adults, the evidence for preventing disease is weak. The USPSTF found it insufficient for heart disease and cancer, and the NIH says most studies show little or no effect. They are worth it when they fill a known gap, such as folic acid before pregnancy or B12 on a vegan diet.

Who should take a multivitamin?

Official guidance points to specific groups: anyone who could become pregnant (a multivitamin with 400 micrograms of folic acid in Canada), pregnant people, older adults who may absorb less B12, vegans, people on very low-calorie or restricted diets, and people after weight-loss surgery, whose team prescribes a specific regimen.

Can you take too many vitamins?

Yes. Multivitamins can push some nutrients past safe limits, especially iron, vitamin A, zinc, niacin and folic acid, if you also take other supplements or fortified foods. Add up everything you take. Too much vitamin A in pregnancy can harm the baby, and high iron doses can be fatal to children.

Should I take a multivitamin if I'm vegan?

You don't necessarily need a full multivitamin, but you do need a reliable source of B12, because it isn't found naturally in plant foods. The NHS also suggests fortified foods or supplements for vitamin D, iodine, selenium and calcium. A targeted vegan supplement or fortified foods can cover these.

Sources

General information, not medical advice — see our medical disclaimer. Written to the WhereToStart editorial policy. Next scheduled review: 20 April 2027.

Do I need a multivitamin? What does the evidence say by age and diet?