Goal · Immune support
Food and the immune system: the nutrients it needs and what trials show
Your immune system needs adequate zinc, vitamin C and vitamin D, which a varied diet usually supplies. Extra beyond that has small, specific effects at best; vaccines, sleep and handwashing do more.
By the editors of Alimentotherapy Last reviewed 4 min read Not medical advice
The short answer
The immune system needs zinc, vitamin C and vitamin D to work normally, and the NIH Office of Dietary Supplements sets daily amounts most people can meet from food NIH ODS; NIH ODS; NIH ODS. Taking more than you need has not been shown to make you less likely to catch a cold, though regular vitamin C and zinc lozenges started early slightly shortened colds in trials Hemila 2013; Nault 2024. The evidence-based protection against flu is the yearly vaccine CDC.
Foods and herbs for immune support, graded
Every claim from our remedy pages that relates to immune support, strongest evidence first. Each row links to the full page and its sources.
| Food or herb | Grade | What the research found |
|---|---|---|
| ProbioticsFewer upper respiratory infections (colds) | Limited | A Cochrane review of 23 trials (6,950 people) found probiotics may reduce the number of people with at least one upper respiratory infection (risk ratio 0.76) and may shorten episodes by about a day, mostly on low-certainty evidence. |
Nutrients the immune system needs
Getting enough matters; getting more than enough is a different claim. Per the NIH Office of Dietary Supplements:
- Zinc helps the immune system fight off invading bacteria and viruses. Adults need 8 mg (women) or 11 mg (men) a day, and the upper limit from all sources is 40 mg. Vegetarians and vegans are more likely to run low NIH ODS.
- Vitamin C helps the immune system work properly. Adults need 75 mg (women) or 90 mg (men) a day, plus 35 mg for smokers, with an upper limit of 2,000 mg NIH ODS.
- Vitamin D is needed by the immune system to fight off bacteria and viruses. Adults need 15 mcg (600 IU) a day, or 20 mcg (800 IU) from age 71. Very few foods contain it naturally, and older adults, people with dark skin and people who rarely get sun make less NIH ODS.
Oysters, meat, fish, poultry, beans, nuts and whole grains supply zinc NIH ODS; citrus, peppers, kiwifruit, broccoli and strawberries supply vitamin CNIH ODS; fatty fish and fortified milk, plant milks and cereals supply most vitamin D. A blood test is one way to find out whether your vitamin D is lowNIH ODS.
Zinc lozenges and vitamin C for colds
Vitamin C. The Cochrane review found regular vitamin C did not lower the chance of catching a cold in the general population, but shortened colds by about 8% in adults and 14% in children. Starting it once a cold had begun showed no consistent effect Hemila 2013.
Zinc. The 2024 Cochrane review (34 trials, 8,526 people) found that zinc may make little or no difference to the chance of catching a cold; used once symptoms start, it may shorten a cold by about two days, with low certainty, and non-serious side effects were more common Nault 2024. An analysis of individual data from three zinc acetate lozenge trials (199 patients, 80 to 92 mg of zinc a day) found 70% of the zinc group had recovered by day five, against 27% on placebo Hemila 2017. The NIH fact sheet sums it up: lozenges started early may speed recovery but do not seem to change how bad symptoms are, and the best dose and form are unsettled NIH ODS. Those lozenge doses are above the 40 mg upper limit, so use them for a few days only, not as a daily habit.
Garlic, elderberry and echinacea are graded on their own pages and in the table on this page; the elderberry vs echinacea page sets them side by side. For everyday cold care, see colds.
What protects you more than any food
Vaccines. The CDC recommends a flu vaccine every season for everyone 6 months and older, with rare exceptions, and calls it the best way to reduce the risk of flu and its serious complicationsCDC. Ask your clinician or pharmacist which other vaccines are due for your age.
Sleep. In a study where 164 healthy adults had their sleep measured for a week and were then given a cold virus, those sleeping under 6 hours were more likely to develop a cold than those sleeping more than 7 Prather 2015.
Handwashing. The CDC calls handwashing with soap one of the best ways to stay healthy and to stop respiratory and diarrheal infections spreading CDC.
Be wary of 'immune' products
Check the label of any "immune" product, and add up what you take from all of them. Megadose products can push zinc above the 40 mg daily upper limit and vitamin C above 2,000 mg, the most the NIH advises from all sources combined NIH ODS; NIH ODS. If you have a condition or take a medicine that weakens the immune system, ask your clinician rather than a label.
When to see a clinician, not the pantry
- Trouble breathing, chest pain, or a high fever that will not come down.
- Infections that keep coming back, are unusually severe, or take much longer than usual to clear.
- A fever while you take a medicine that weakens the immune system, such as chemotherapy or a transplant drug: call your care team straight away.
- Losing weight without trying, night sweats or swollen glands that last more than a couple of weeks.
Common questions
What vitamins does the immune system need?
The NIH Office of Dietary Supplements says the immune system needs zinc, vitamin C and vitamin D to fight off bacteria and viruses. Adults need 8 to 11 mg of zinc, 75 to 90 mg of vitamin C and 15 mcg (600 IU) of vitamin D a day, or 20 mcg after age 70, mostly reachable from food.
Do zinc lozenges help a cold?
They may shorten it if started early. The 2024 Cochrane review estimated about two days shorter, with low certainty, and an analysis of three zinc acetate lozenge trials found 70% recovered by day five versus 27% on placebo. Lozenges do not seem to make symptoms milder, and daily zinc did not stop colds.
Does vitamin C stop you catching colds?
Not in the general population. A Cochrane review found regular vitamin C did not reduce the chance of catching a cold but shortened colds by about 8% in adults and 14% in children. Taking it after a cold starts showed no consistent benefit.
Sources
Primary research and government sources, each checked on the date this page was reviewed.
- NIH ODSNIH Office of Dietary Supplements. Zinc: Fact Sheet for Consumers.
- NIH ODSNIH Office of Dietary Supplements. Vitamin C: Fact Sheet for Consumers.
- NIH ODSNIH Office of Dietary Supplements. Vitamin D: Fact Sheet for Consumers.
- CochraneHemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013. PMID 23440782.
- CochraneNault D, et al. Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev. 2024. PMID 38719213.
- PubMedHemilä H, et al. Zinc acetate lozenges may improve the recovery rate of common cold patients: an individual patient data meta-analysis. Open Forum Infect Dis. 2017. PMID 28480298.
- PubMedPrather AA, et al. Behaviorally assessed sleep and susceptibility to the common cold. Sleep. 2015. PMID 26118561.
- GuidelineCenters for Disease Control and Prevention. Key Facts About Seasonal Flu Vaccine.
- GuidelineCenters for Disease Control and Prevention. About Handwashing.
Keep reading
- GoalFood and colds: honey, zinc, vitamin C and chicken soupNo food stops a cold. Honey has good evidence for easing cough in children over one, and regular vitamin C slightly shortens colds; most other remedies are comfort.
- RemedyGarlicGarlic supplements have shown small drops in blood pressure in people with hypertension. The cholesterol and cold evidence is weaker, and supplements can interact with some drugs.
- RemedyElderberryA popular syrup with a short, conflicting trial record. Early small studies suggested faster recovery from flu; the most carefully run recent trial found none. Raw berries are toxic until cooked.
- RemedyEchinaceaOne of the most-tested herbs for colds. The trials point to, at best, a small drop in the chance of catching a cold and no clear effect on how long one lasts.
- ComparisonElderberry vs echinacea for coldsBoth are sold for colds, and both have thin evidence. Elderberry has a few small positive trials and one careful negative one; echinacea's big Cochrane review found little effect on how long a cold lasts.