Key takeaways
- Ten nutrients have an authorised claim for the normal function of the immune system (UK and EU): vitamins A, B6, B12, C, D, folate and copper, iron, selenium, zinc. A product needs only 15% of the NRV of one of them per daily dose to use it.
- "Boosts" or "stimulates" your immune system is not an authorised claim. No supplement has been shown to make a healthy immune system work better than normal.
- Echinacea, elderberry, propolis and other botanicals have no authorised claim. In a Cochrane review, echinacea showed at best a weak, uncertain effect on colds.
- The 2025 update of the largest vitamin D meta-analysis (46 trials, over 64,000 people) found no statistically significant protection against respiratory infections overall. Vitamin D in winter is about avoiding a deficiency.
- The best evidence for colds is modest: zinc started early may shorten a cold by about two days, and daily vitamin C shortens colds by about 8% in adults.
The short answer
No supplement makes a healthy immune system work “better”. What the law allows, and what the evidence supports, is narrower: ten vitamins and minerals contribute to the normal function of the immune system, which matters if you are short of one of them. In winter, the nutrient most people in northern Europe run low on is vitamin D. For colds, the best evidence is for zinc started early and daily vitamin C, and even there the effects are small.
What “supports your immune system” on a label means
UK and EU law allow exactly one immune claim for ten nutrients: the nutrient contributes to the normal function of the immune system. A product may use it as soon as a daily dose gives 15% of the NRV (the reference intake printed on labels) of one of them.
| Nutrient | Minimum per daily dose for the claim (15% NRV) | Good to know |
|---|---|---|
| Vitamin C | 12 mg | A second claim covers intense exercise: 200 mg on top of the normal intake |
| Vitamin D | 0.75 µg | A separate claim covers children; the NHS advises 10 µg a day in autumn and winter |
| Zinc | 1.5 mg | Long-term high doses block copper absorption |
| Selenium | 8.3 µg | Brazil nuts are a rich food source |
| Vitamin A | 120 µg | Avoid supplements with vitamin A in pregnancy |
| Vitamin B6 | 0.21 mg | High doses over time can damage nerves |
| Vitamin B12 | 0.38 µg | Essential to supplement on a vegan diet |
| Folate | 30 µg | |
| Iron | 2.1 mg | Only take iron if you need it; see our iron guide |
| Copper | 0.15 mg |
Two things follow:
- The threshold is low. A gummy with 12 mg of vitamin C may print the same immune claim as a tablet with 1,000 mg. The claim tells you a nutrient is present, not that the dose does anything extra.
- The wording is fixed. UK guidance on claim wording accepts “supports the normal function of the immune system”, but not “stimulates” or “optimises”. “Boost your defences” is marketing, not an authorised claim.
What trials show for winter colds
| Supplement | What the best review found | Certainty |
|---|---|---|
| Vitamin D, daily | 2025 meta-analysis of 46 trials (64,086 people): a small effect on respiratory infections that is no longer statistically significant overall; daily dosing looked better than large weekly or monthly doses | Moderate; overall result not significant |
| Vitamin C, daily | Does not prevent colds in the general population; shortens them by about 8% in adults and 14% in children (Cochrane 2013) | Moderate |
| Zinc, started early | May shorten a cold by about 2 days; no clear benefit for prevention (Cochrane 2024) | Low |
| Probiotics | May reduce the number of people with at least one upper respiratory infection (Cochrane 2022); depends on the strain | Low |
| Echinacea | No clear benefit for treatment; non-significant trends for prevention, of questionable clinical relevance (Cochrane 2014) | Low |
The details for vitamin C and zinc, including doses and side effects, are in zinc and vitamin C for colds.
Echinacea, elderberry, propolis: no authorised claim
Claims for plants and plant extracts have been on hold in the EU since 2010, and Great Britain took over the same list in 2021. None has been authorised since, so echinacea, elderberry and other herbal “immune” products cannot rely on an authorised claim. Bee products such as propolis and royal jelly are not on the authorised list either.
This is why so many winter complexes add a small amount of vitamin C or zinc: it is the ingredient that carries the legal claim on the pack, while the herb takes the space on the front. Our guide to approved health claims explains how the system works.
Vitamin D: the one most people actually need in winter
Between about October and March the sun in the UK and most of Europe is too weak for your skin to make vitamin D. The NHS advises everyone to consider 10 µg (400 IU) a day in autumn and winter, and all year for people who are rarely outdoors, cover their skin or have dark skin. That advice is about bones and muscles, and about not running low; it is not a promise of fewer colds. See vitamin D in a European winter for who needs more and how to choose a product.
What to check before you buy
- Find the nutrient behind the claim. If the front says “immune” and the back lists 12 mg of vitamin C next to a herb, the claim rests on the vitamin C.
- Don’t stack high doses. An immune complex, a multivitamin and a separate zinc tablet can add up to more than the NHS figure of 25 mg zinc a day. The NHS says less than 1,000 mg of vitamin C a day is unlikely to cause harm; Germany’s BfR advises at most 250 mg per daily dose in a supplement.
- Check the maximum in your country. Limits differ a lot; our maximum levels guide has the table.
- Be wary of “shots” and gummies sold for immunity: they often give small amounts of vitamins with added sugar.
Compare the ingredients and the products we have checked on our immune support page.
FAQ
Which supplements are allowed to say they support the immune system?
Vitamins A, B6, B12, C, D and folate, and the minerals copper, iron, selenium and zinc. Each may claim to contribute to the normal function of the immune system if a daily dose provides at least 15% of its NRV. No herb, probiotic or bee product has an authorised immune claim.
Can you boost your immune system with supplements?
Not in the sense the word suggests. The authorised claims say a nutrient contributes to the normal function of the immune system: that matters if you are short of it. UK guidance on claim wording says terms such as "stimulates" or "optimises" are not acceptable.
Does vitamin D prevent colds?
Not clearly. The 2025 update of the largest meta-analysis of vitamin D trials found a small effect that was no longer statistically significant overall. Daily doses looked better than large weekly or monthly ones. The NHS still advises 10 µg a day in autumn and winter to avoid deficiency.
Does echinacea work?
A 2014 Cochrane review of 24 trials found no clear benefit for treating colds and only non-significant trends for prevention, of questionable clinical relevance. Products differ greatly by plant species and part, and echinacea has no authorised health claim.
Do probiotics help against colds?
A 2022 Cochrane review found that probiotics may reduce the number of people who get at least one upper respiratory infection, on low-certainty evidence, with results depending on the strain. No probiotic has an authorised health claim.
Sources
- European Commission — EU Register of nutrition and health claims
- Commission Regulation (EU) No 432/2012 — list of permitted health claims
- Commission Regulation (EU) 2016/1389 — vitamin D and the immune system in children
- DHSC — Health claims, principles on flexibility of wording (2012)
- DHSC — Great Britain nutrition and health claims (NHC) register
- Jolliffe DA et al. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Lancet Diabetes Endocrinol, 2025
- Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev, 2013
- Nault D et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev, 2024
- Zhao Y et al. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev, 2022
- Karsch-Völk M et al. Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev, 2014
- NHS — Vitamin D
- NHS — Vitamin C
- EFSA — Overview of tolerable upper intake levels (2024)