Foods that support your immune system: what the research says

Every winter the "immune-boosting foods" lists come round again, and most of them are the same 15 foods with the same vague promises. The honest version is shorter and more useful. You can't "boost" an immune system that's working normally, and you wouldn't want to; an over-active immune system is what allergy and autoimmune disease are. What you can do is stop short-changing it. The immune system is built and run from nutrients, sleep and movement, and when any of those is short, it shows. Here's what the research supports, and what it doesn't.

What "supports immunity" means

Immune cells are made from protein, turn over quickly, and depend on a handful of vitamins and minerals to work: vitamins A, C, D and E, zinc, selenium, iron and folate among them. A 2020 review of the evidence put it plainly: deficiency in any of these impairs immune function, and correcting it restores it. That's the whole mechanism. Food can't make a replete immune system stronger, but a lot of people aren't replete, particularly for vitamin D, zinc and iron, and the fix is on the plate.

The foods that do the work

Protein at every meal. Antibodies and immune cells are protein, and a protein-short diet is the most reliable way to weaken a defence. Eggs, fish, chicken, meat, dairy, legumes, and, yes, a scoop of collagen in your coffee counts towards the day's total. Women over 40 tend to under-eat protein, and this is one of the reasons it matters.

Vitamin C foods: red peppers, citrus, kiwi, broccoli, strawberries. The famous one, and the one most people over-rate. The Cochrane review of 29 trials found that taking vitamin C every day does not stop ordinary people catching colds; it shortens them slightly, by about 8% in adults, roughly half a day. The exception is people under heavy physical stress (marathon runners, soldiers in the cold), where regular vitamin C halved the number of colds. Eat the foods, which is easy; 1 red pepper covers the day. A large dose once you're already ill does little.

Vitamin D: oily fish, egg yolks, and sunlight. The best-supported of the lot. A 2017 analysis of 25 trials in nearly 11,000 people found vitamin D supplements cut acute respiratory infections by about 12% overall, and the benefit was concentrated in people who started out deficient. Food alone rarely supplies enough; 15 minutes of midday sun on arms and legs in summer does, and in a Johannesburg or Cape winter, a modest supplement is reasonable. Ask your doctor for a level if you're not sure.

Zinc: meat, shellfish, pumpkin seeds, legumes, cheese. Zinc deficiency is common in older adults and plant-based eaters, and it directly weakens immune cells. For colds specifically, zinc acetate lozenges started within 24 hours shortened them by about a third in a 2017 meta-analysis, which is better than vitamin C manages. That's lozenges at the first scratch, not daily tablets.

Selenium: 1 or 2 Brazil nuts a day. Needed for several immune enzymes, and 2 Brazil nuts cover it. More isn't better; selenium is toxic in excess, so this is not a food to eat by the handful.

Fermented foods: plain yoghurt, kefir, sauerkraut, kimchi. About 70% of the immune system sits in the gut wall, and the bacteria living there train it. Live-culture foods help keep that population diverse. Choose plain yoghurt with "live cultures" on the label, and sweeten it yourself.

Colour: dark leafy greens, carrots, sweet potato, berries. Vitamin A (as beta-carotene) keeps the linings of the nose, throat and gut intact, which is the immune system's first wall. Berries and greens bring the polyphenols that the "antioxidant" claims are based on. The evidence for any single food is thin; the evidence for a diet with a lot of vegetables in it is strong.

Garlic, ginger and turmeric. They're on every list, so here's the honest line: good flavours, some lab and animal evidence, little human evidence for preventing infection. Cook with them because they're delicious. Don't rely on them.

The things that undo it

• Short sleep. In a study that exposed 164 volunteers to a cold virus, people sleeping under 6 hours a night were 4 times more likely to come down with the cold than people sleeping 7 hours or more. Sleep is the single largest lever on this list, and no food replaces it. Our sleep article covers it.
• Alcohol, which suppresses immune cells for hours after each drink and wrecks sleep.
• Chronic stress. Cortisol dampens the immune response; the stress article has the practical part.
• Sitting still, and over-training. Regular moderate exercise (a brisk daily walk) is linked to fewer infections; very hard, long training temporarily does the opposite, which is why the marathon runners needed the vitamin C.
• Smoking, which damages the airway lining that keeps viruses out.

What about supplements?

They fix deficiencies, and that's their job. Vitamin D in winter if your level is low; zinc lozenges at the first sign of a cold; a multivitamin if your diet is patchy. What they don't do is lift a replete person's immunity above normal, and the mega-dose products sold on that promise have no evidence behind them. If you take anything long-term, know why, and know your level.

Frequently asked questions

What is the best food for the immune system?
There isn't one. The closest honest answer is "enough protein, enough vitamin D, and vegetables at every meal". Any list that crowns a single superfood is selling it.

Does vitamin C prevent colds?
Not in ordinary daily life, according to the Cochrane review. It shortens them slightly, and it prevents them in people under extreme physical stress. Eat the foods; skip the 1,000 mg tablets.

Does collagen support the immune system?
As protein, yes, in the ordinary way all protein does. It isn't an immune product and we don't sell it as one. Its own evidence is for skin, joints and bone, which you can read in our collagen library.

Should I take vitamin D in winter?
If your level is low, yes, and in South Africa's winter a lot of people's are, especially with darker skin or an indoor job. Ask your doctor for a blood test rather than guessing a dose.

Can food protect me from flu or Covid?
No food or supplement prevents a specific infection, and nothing here replaces vaccination where it's recommended for you. Good nutrition gives a normal immune system the materials to do its job; that's the claim, and it's enough.

The sources

• Gombart AF, Pierre A, Maggini S (2020). A review of micronutrients and the immune system: working in harmony to reduce the risk of infection. Nutrients 12:236. View →
• Hemilä H, Chalker E (2013). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews CD000980. 29 trials, 11,306 participants. View →
• Martineau AR et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ 356:i6583. 25 trials, 10,933 participants. View →
• Hemilä H (2017). Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open 8:2054270417694291. View →
• Prather AA, Janicki-Deverts D, Hall MH, Cohen S (2015). Behaviorally assessed sleep and susceptibility to the common cold. Sleep 38:1353–1359. View →

Find out more

• How sleep improves your health
• Tips to reduce stress naturally
• 6 health benefits of staying hydrated
• The collagen library

This article is general information, not medical advice. If you're getting infections more often than seems right, or they're taking longer to clear, that's a reason to see a doctor, not to change your shopping list.

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