“Take more vitamin D
to stop getting sick” is
more complicated than it sounds.
Getting sick often — catching every cold that goes round the office, the school gate or the metro — isn’t just bad luck. Vitamin D, zinc and vitamin C are all genuinely involved in how your immune system works. But the popular advice — “take vitamin D”, “suck on zinc”, “load up on vitamin C” — skips over research that is more specific, and more useful, than a blanket fix.
Worth saying first: frequent illness has many causes beyond nutrition — stress, poor sleep, allergies and medical conditions among them. This guide covers the nutrition side. Genuinely frequent or severe illness deserves a doctor’s evaluation, not a guess.
Vitamins for immunity: why nutrients matter at all
Immune cells need specific nutrients to develop and work properly. Vitamin D, vitamin C, zinc, vitamin B6, vitamin B12 and folate all contribute to the normal function of the immune system. A real shortfall can leave that system working below par — but taking more than you need doesn’t turn it into a super-system.
Your immune system isn’t one thing — it’s a network of specialised cells that have to be built correctly and supplied properly to do their job. Several nutrients are directly involved: vitamin D, vitamin C, zinc, vitamin B6, vitamin B12 and folate (Vitamin B9) all contribute to the normal function of the immune system.1 That part is settled biology.
The harder question — and the one most advice skips — is whether taking more of any single nutrient, once you already have enough, means fewer colds. Think of the parent whose child brings home every bug from school, the analyst on a packed Delhi metro every morning, or the runner deep in a training block. The answer is different for each nutrient, and it’s more specific than “yes”.
Zinc for colds: real evidence — at a dose most people don’t realise
Zinc lozenges can shorten a cold, but only at high doses. Trials giving more than 75 mg of zinc a day as zinc acetate lozenges cut cold duration by about 42%; trials below 75 mg a day found no effect. That is a short-term treatment started at the first symptoms — not the same thing as a daily zinc supplement.
The popular claim “zinc helps colds” is true but incomplete. When researchers pooled every placebo-controlled lozenge trial, the results only made sense once they looked at the dose. Five trials giving less than 75 mg of zinc a day found no effect at all. Three trials using zinc acetate above 75 mg a day shortened colds by 42%, and other zinc salts at similar doses by about 20%.2
A follow-up analysis of the three zinc acetate trials, at 80–92 mg a day, found shorter nasal discharge, congestion, sore throat, hoarseness, cough and muscle aches — but no clear effect on headache or fever. The authors’ conclusion was specific: lozenges at about 80 mg a day, started within 24 hours of symptoms and used for less than two weeks.3
So a daily zinc supplement — typically around 10–15 mg — is a different tool. It supports normal immune function and helps correct a shortfall over time, but it isn’t shown to shorten a cold you already have. Treating the two as interchangeable oversells both. (Our zinc deficiency guide covers the everyday side.)
If you use zinc daily, look for a chelated form such as zinc bisglycinate, a sensible dose (around 10–15 mg), and copper alongside it — long-term zinc on its own can quietly drain your copper. If you’re buying lozenges for a cold, check the zinc per lozenge and the form: the positive trials used zinc acetate.
Vitamin D and immunity: a small, uncertain effect on colds — and why it still matters
The largest analysis of vitamin D and respiratory infections (2025, over 60,000 people) found a small reduction in risk that was not statistically significant, with no clear difference by starting vitamin D level or dosing schedule. Vitamin D still contributes to normal immune function — so correcting a deficiency makes sense, but it isn’t a proven cold shield.
This is the claim that has shifted most. A 2021 meta-analysis of 46 trials found vitamin D slightly reduced the risk of respiratory infections, with protection showing up mainly in daily doses of 400–1,000 IU.4 But the 2025 update, adding several large new trials, found the overall effect was small and no longer statistically significant — and it found no clear difference by baseline vitamin D level, dose size or dosing frequency.5
That doesn’t make vitamin D irrelevant. It contributes to normal immune function, bones and muscles,1 and deficiency is extremely common in India — most Indian studies find 80–90% of adults below the healthy range, indoor lives and all.6 The honest position: fix a real deficiency with a steady daily dose, for everything vitamin D does — just don’t expect it to stop colds on its own. Our vitamin D guide covers testing and dosing.
“The research doesn’t say vitamin D is useless for immunity. It says the effect on catching colds is small and uncertain — so treat it as fixing a gap, not buying a shield.”
What the 2025 evidence actually supports
Vitamin C for colds: the surprise is who it works for
Across 29 trials and 11,306 people, regular vitamin C did not change how often ordinary people caught colds. It modestly shortened colds, and it halved the risk of catching one only in people under extreme physical stress, such as marathon runners, skiers and soldiers. Those trials used at least 200 mg a day.
Vitamin C is the most popular “immunity” supplement, and the evidence is clear — just not in the way most people assume. In the Cochrane review, regular vitamin C had no effect on how often the general population caught colds. It did produce a modest, consistent reduction in how long colds lasted. And in five trials of people under short bursts of extreme physical stress — marathon runners, skiers, soldiers on sub-arctic exercises — it halved the risk of catching a cold. Taking large doses only once a cold had started showed no consistent benefit.7
Those trials all used 200 mg a day or more. Vitamin C still contributes to normal immune function and to collagen formation at everyday doses,1 but if you’re training for an ultra or a HYROX race, that higher-dose finding is the one that applies to you. Our vitamin C guide covers the everyday role.
Other real causes of getting sick often
Frequent illness usually has more than one cause. Chronic stress, short sleep, allergies, heavy exposure (young children, crowded commutes, travel), air pollution and underlying medical conditions all play a part. Nutrition is one factor you can test and correct — not the automatic explanation.
Common non-nutritional causes
- Chronic stress and short sleep, both of which affect immune function
- Allergies, which can mimic or worsen “always sick” symptoms
- Heavy exposure — young children at home, crowded commutes, frequent travel
- Air pollution, which irritates the airways
- Underlying medical conditions, including immune deficiencies
Where nutrition fits
- Vitamin D, zinc and vitamin C each have documented immune roles
- Testing your levels beats assuming one fix suits everyone
- Worth checking alongside — not instead of — a proper medical evaluation
When getting sick often is worth a doctor’s visit
See a doctor if you’re ill more often than every few weeks, if infections are unusually severe or slow to clear, if a fever lasts more than a few days, or if you notice breathlessness, unexplained weight loss or night sweats. A doctor can look for causes that no supplement will fix.
Daily nutrients for normal immune function — at honest doses.
Two products cover the nutrients in this guide, kept separate on purpose so minerals and vitamins don’t compete for absorption. Neither is a cold treatment — they’re the everyday baseline.
Bioactive Multivitamin
600 IU vegan vitamin D3 every day — a steady daily dose in the range the 2021 analysis flagged — plus 80 mg buffered vitamin C, and active B6, B12 and folate, all of which contribute to normal immune function. One capsule at breakfast.
See the multivitamin →Element 5
13 mg zinc bisglycinate balanced with 1.3 mg copper — a maintenance dose for normal immune function, not a high-dose lozenge protocol — alongside 300 mg magnesium. Two capsules in the evening.
See Element 5 →What to actually do if you keep getting sick
See a doctor first if illness is frequent or severe. Then check your vitamin D and B12, cover the everyday nutrients with a steady daily routine, and save high-dose zinc lozenges for the first day of a cold. If you train hard, vitamin C at 200 mg or more is the evidence-backed extra.
- See a doctor if illness is frequent or severeRecurrent or stubborn infections can have causes beyond nutrition that need proper evaluation.
- Test before you guessA 25-OH vitamin D test and a B12 test tell you whether a real gap exists.
- Cover the basics every daySteady daily vitamin D, vitamin C, zinc and B-vitamins at normal doses — alongside sleep and stress, which matter just as much.
- Use zinc lozenges only as a short treatmentThe evidence supports zinc acetate above 75 mg a day, started within 24 hours of symptoms, for under two weeks.
- Add vitamin C if you train hardThe halved-risk finding applies to heavy physical stress, at 200 mg a day or more.
Immunity and nutrients, answered plainly.
Why do I get sick so often?
Does vitamin D prevent colds?
Do zinc lozenges work for colds?
Is a daily zinc supplement the same as zinc lozenges?
Does vitamin C prevent colds?
Which nutrients support the immune system?
Is getting sick often a sign of a nutrient deficiency?
When should I see a doctor about getting sick often?
Can a multivitamin help me get sick less often?
Why are these nutrients split across two Evo Hominus™ products?
Studies behind this guide
- European Commission. Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods (vitamin D, vitamin C, zinc, vitamin B6, vitamin B12, folate — normal function of the immune system). Official Journal of the European Union. 2012;L136:1–40.
- Hemilä H. Zinc lozenges may shorten the duration of colds: a systematic review. Open Respir Med J. 2011;5:51–58 — 13 trial comparisons; no effect below 75 mg/day, 42% shorter colds with zinc acetate above 75 mg/day.
- Hemilä H, Chalker E. The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis. BMC Fam Pract. 2015;16:24. PMID 25888289 — three trials, 80–92 mg zinc/day.
- Jolliffe DA, et al. Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials. Lancet Diabetes Endocrinol. 2021;9(5):276–292. DOI 10.1016/S2213-8587(21)00051-6.
- 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;13(4):307–320. PMID 39993397 — OR 0.94 (95% CI 0.88–1.00); no effect modification by baseline status, dose or frequency.
- Aparna P, Muthathal S, Nongkynrih B, Gupta SK. Vitamin D deficiency in India. J Family Med Prim Care. 2018;7(2):324–330. PMID 30090772
- Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;(1):CD000980. PMID 23440782 — 0.2 g/day or more; 29 comparisons, 11,306 participants.
Nutrition Science Hub
Why most Indians are low in vitamin D
Testing, dosing, and why sunshine alone doesn’t fix it.
Read the guide → ZincZinc deficiency in India
The everyday role of zinc, beyond colds — and the best-absorbed forms.
Read the guide → Zinc & copperWhy zinc needs copper
The quiet depletion long-term zinc can cause — and the 10:1 fix.
Read the guide →