Immunity: what strengthens it (beyond vitamin C)

"Boost your immunity" has been one of the most durable wellness slogans of the last twenty years. Most of what gets sold under that banner does not meaningfully change how your immune system works. Here's the evidence-aware version — what matters for everyday immune function, which nutrients carry authorised UK and EU claims, and what to put in your cupboard.

How your immune system works (in short)

Your immune system is not a single thing you can "boost" — it is a distributed, layered set of cell types, chemical signals, and physical barriers running constantly in the background. Innate immunity (the always-on first line: skin, mucous membranes, certain white blood cells). Adaptive immunity (the memory-based second line: B cells, T cells, antibodies). Both layers need raw materials from your diet, recovery time from your sleep, and signals from the rest of your physiology that you are not under sustained stress.

"Strengthening" immunity, in any meaningful sense, is about removing deficits — not about adding more of things you already have plenty of.

The nutrients with authorised EU/UK immune-function claims

There are only a handful of nutrients with formally authorised claims that contribute to the normal function of the immune system. They are worth memorising.^[1]

• Vitamin D — contributes to the normal function of the immune system. The single most common UK nutrient shortfall in winter; covered in depth in our vitamin D guide and paired with K2 in our Vitamin D3+K2.
• Vitamin C — contributes to the normal function of the immune system during and after intense physical exercise (specific claim); also contributes to normal immune function more broadly.^[2]
• Zinc — contributes to the normal function of the immune system.
• Selenium — contributes to the normal function of the immune system.
• Copper — contributes to the normal function of the immune system.
• Iron — contributes to the normal function of the immune system.
• Vitamin A — contributes to the normal function of the immune system.
• Folate (B9) — contributes to the normal function of the immune system.
• Vitamin B6 — contributes to the normal function of the immune system.
• Vitamin B12 — contributes to the normal function of the immune system.

Anything not on this list — echinacea, elderberry, sambucus, mushroom blends, fancy-branded immune complexes — does not carry an authorised EU immune claim, regardless of what the front of the box says.

The two most common UK shortfalls

Vitamin D through winter. At UK latitude, the sun is too low from October to March to drive meaningful skin synthesis of vitamin D. Most British adults sit below the sufficiency threshold by late February on a typical diet. SACN recommends 10 µg/day from October through March for the general population.^[3] Supplementing 10-25 µg of D3 daily through the darker half of the year is the single most useful immune-related nutritional move for most UK adults.

Low zinc intake on plant-leaning diets. Zinc from plants is less bioavailable than from animal foods; diets that exclude or minimise red meat, shellfish, and dairy can run low. A 2014 review of B12 status in vegetarians and vegans found high deficiency rates particularly in vegans, infants and pregnant women — worth checking alongside zinc when on a plant-leaning diet.^[4] Pumpkin seeds, legumes, and wholegrains help but often are not enough on their own.

Why we pair vitamin D with K2

Our Vitamin D3+K2 MK-7 combines the D3 behind the immune and bone claims with K2 in the MK-7 form that covers the calcium-direction biochemistry. MK-7 has a notably longer plasma half-life than K1, which is why daily supplementation gives stable serum levels.^[5] One capsule a day through autumn and winter covers the immune-relevant D3 dose and keeps the downstream calcium pathway running coherently. Fuller discussion in our D3+K2 guide.

Where omega-3 fits

Omega-3 does not carry an authorised immune health claim specifically, but the research on EPA and DHA in broader inflammatory and immune biology is active and interesting. EPA and DHA contribute to normal heart function (authorised, at 250 mg/day combined), and the inflammatory-signalling work that touches immune biology sits next to that.

Both our Omega-3 fish oil and life'sOMEGA algae oil clear the 250 mg daily threshold comfortably.

What vitamin C does (and does not)

Vitamin C has a genuine immune role — one of the authorised claims covers exactly that. NHS guidance is that vitamin C is needed for the normal functioning of the immune system; most adults can get enough from a varied diet (citrus, peppers, kiwi, broccoli) at 40 mg/day for adults.^[2] What it does not do is "prevent a cold when you take a handful at the first sneeze." The Cochrane review of vitamin C and common colds has been clear for years: regular daily intake in the normal range may reduce the duration of symptoms slightly; megadosing at symptom onset does not.

The non-supplement factors that matter more

• Consistent sleep — the single biggest immune lever. One night of significant sleep loss measurably impairs immune function markers the next day.
• Adequate protein. Your immune cells are proteins; producing them requires amino acids.
• Movement on most days. Moderate activity is associated with fewer infections; sedentary and over-trained both correlate with more.
• Fruit and vegetable diversity. The dietary polyphenols and fibre that feed the gut microbiome are part of the immune picture in ways we are still mapping.
• Stopping smoking. Nothing else a supplement can do comes close to the immune impact of quitting.

A sensible daily immune-support routine

1. Vitamin D3+K2 daily through autumn and winter — covers the single biggest UK nutrient gap.
2. Omega-3 daily (fish oil or algae) — at least 250 mg EPA+DHA.
3. Zinc and selenium from food — oysters, pumpkin seeds, Brazil nuts, legumes. A B-complex covers the Bs and folate.
4. Food variety and colour. If your plate looks monochromatic, that is a signal.
5. Sleep discipline and stress discipline. Supplements cannot out-run chronic sleep debt.

Who should speak to a doctor first

• Anyone with an immune-compromising condition — these need individualised medical guidance, not supplement self-prescription.
• Anyone on immunosuppressant medications — check interactions before starting new supplements.
• Anyone with a recent significant change in immune function — frequent infections, unusual fatigue, unexplained fevers — investigate first.

In practice

Real immune support is a short list of authorised-claim nutrients (especially vitamin D through winter), adequate sleep, moderate movement, and a diverse diet. Anything sold as a dramatic "immune booster" is mostly marketing. The supplement layer worth paying for is the one that closes the genuine nutritional gaps.

References

1. European Commission. EU Register of Nutrition and Health Claims Made on Foods. ec.europa.eu
2. NHS. Vitamin C. nhs.uk
3. Scientific Advisory Committee on Nutrition. SACN Vitamin D and Health Report (2016). gov.uk
4. Pawlak R, Parrott SJ, Raj S, Cullum-Dugan D, Lucus D. How prevalent is vitamin B(12) deficiency among vegetarians? Eur J Clin Nutr. 2014;68(5):541–548. PubMed: 24667752
5. Schurgers LJ, Teunissen KJF, Hamulyák K, et al. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8):3279–3283. PubMed: 17158229

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