Every September, the same ritual starts again: someone in the office sneezes, and by Wednesday half the building is necking vitamin C tablets like it's a race. It isn't, quite. But it isn't nothing either β the confusion mostly comes from people arguing past each other about what vitamin C is actually proven to do.
What vitamin C actually does once it's in your system
Vitamin C contributes to the normal function of the immune system β that's not a marketing line, it's the wording of the authorised health claim itself, evaluated and approved by the European Food Safety Authority.[1] It also helps with collagen formation, iron absorption and protecting cells from oxidative stress, which is why it shows up in everything from skin supplements to post-workout blends. Your body can't make it and can't store much of it, so unlike vitamin D or B12, there's no topping up a reserve β you need a fresh supply, ideally daily.[2]
The cold study everyone quotes half of
Here's where it gets more interesting, and slightly less flattering for vitamin C than the supplement aisle would have you believe. The most cited body of evidence β a long-running Cochrane review led by the Finnish researcher Harri HemilΓ€ β found that regular vitamin C supplementation does not reduce your chances of catching a cold in the general population. What it does do, consistently, across dozens of trials, is shorten how long the cold lasts once you've got it: by about 8% in adults and 14% in children.[3] Not nothing. Not a cure, either.
That marathon-runner finding is the detail most headlines leave out. Under genuine physical stress β a race, a cold-weather expedition, sustained heavy training β vitamin C's protective effect on cold risk was far stronger than in everyday life.[3] If you're not in that category, the honest expectation is a shorter cold, not a cold-free winter.
Why the zinc in this bottle comes with copper
Zinc has its own authorised claim β it "contributes to the normal function of the immune system" β plus roles in wound healing and making new cells.[4] Copper carries the same immune-function claim, and it matters here for a less obvious reason: copper and zinc share an absorption pathway in the gut, so a large, sustained dose of zinc on its own can gradually crowd out copper, which is one of the ways high-dose zinc supplementation is linked to copper deficiency and, over time, anaemia.[5] Formulating the two together is a straightforward way to avoid creating a new problem while fixing another.
Worth being upfront about: the NHS guidance is not to exceed 25mg of zinc a day from supplements unless a doctor advises otherwise.[6] A two-capsule dose of a combined vitamin C, zinc and copper formula can sit above that on its own β which is exactly why it's worth checking what else is already covering your zinc before adding a standalone supplement, particularly if you're also taking a multivitamin. If you've never checked what a zinc shortfall actually looks like, we've covered the signs separately β it's worth reading before you assume more is better.
How much you actually need, and when more stops helping
The NHS recommended intake for adults is 40mg of vitamin C a day β achievable from a couple of pieces of fruit and veg, no supplement required.[1] Anything above roughly 1,000mg a day risks stomach pain, diarrhoea or wind, symptoms that resolve once you stop.[1] For zinc, adult men need about 9.5mg and women 7mg from diet alone, with 25mg a day as the sensible ceiling from supplements.[6]
"More vitamin C doesn't mean more immunity. Past a certain point, it just means a less comfortable afternoon."
Two capsules of Oxford Origins' Vitamin C and Zinc Capsules deliver 1200mg of vitamin C, 40mg of zinc and 2mg of copper β a high-strength dose built for someone actively fighting something off, not a daily maintenance top-up. If your stomach runs sensitive, taking it with food helps, and there's a reasonable case for splitting the two capsules across the day β one with breakfast, one with dinner β rather than taking both at once.
A few things worth checking before you add any zinc or vitamin C supplement to your shelf:
- Check your multivitamin first β most all-in-ones already include a meaningful zinc dose, so a standalone high-strength supplement can push your total past the 25mg guidance without you noticing.
- Take with food if needed β high-dose vitamin C on an empty stomach is the most common cause of the stomach upset people blame on "not agreeing with them."
- Match the dose to the moment β a high-strength formula makes more sense during an illness or a run of late nights than as a permanent daily habit.
None of this is about hitting a "gold standard" number on a label. It's about knowing what a claim is actually backed by, and taking the dose that fits what you're using it for β not the biggest one on the shelf.
Frequently asked questions
How long does it take for vitamin C to start helping with a cold?
The evidence is strongest for taking it regularly, before you're ill, rather than starting once symptoms appear. Trials that only began dosing after cold onset generally didn't show the same benefit β the duration reduction shows up in people who were already supplementing when the cold started.
Can you take vitamin C and zinc together every day?
You can, but a high-strength combined dose like 1200mg vitamin C and 40mg zinc is better suited to short, targeted periods β a cold, a run of poor sleep, heavy travel β than an indefinite daily habit, given the NHS's zinc guidance of 25mg or less from supplements long-term.
Is 1000mg of vitamin C a day too much?
Not according to NHS guidance β under 1,000mg a day is considered unlikely to cause harm. Above that, the main risks are digestive: stomach pain, diarrhoea or wind, which clear up once you stop taking it.
Do I need a zinc supplement if I already take a multivitamin?
Possibly not, or not at this strength. Check the zinc dose on your multivitamin's label first β if you're already close to 25mg a day from that alone, adding a high-strength combined formula could take you well past the recommended ceiling. Our guide to zinc deficiency signs covers how to tell if you're actually short in the first place.
Sources
- NHS β Vitamin C: how much you need and safe upper intake. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-c/
- EFSA β Scientific Opinion on vitamin C and contribution to the normal function of the immune system (authorised health claim). https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2015.4298
- HemilΓ€ H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD000980.pub4/full
- EFSA β Scientific Opinion on zinc and normal function of the immune system (authorised health claim). https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2014.3653
- EFSA β Scientific Opinion on copper and maintenance of the normal function of the immune system (authorised health claim). https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2011.2079
- NHS β Others: zinc and copper daily requirements and safe upper intakes. https://www.nhs.uk/conditions/vitamins-and-minerals/others/
At Oxford Origins, your wellbeing is our priority, and although we pride ourselves on our expertise in nutrition and supplementation, it's important to acknowledge the individuality of each person. Articles published by Oxford Origins are not intended to treat, diagnose, cure or prevent any disease, or replace the advice of your GP. We always recommend consulting with a healthcare provider if you encounter any health concerns, and we'll always be here to support you so you're never alone on your journey.
