Cold season creeps in, supermarket shelves brim with citrus, and you reach for fizzing tablets promising defence. The ritual feels reassuring, almost automatic.
Yet the question nags: does vitamin c prevent colds, or shorten them once you are bunged up? Evidence from high‑quality trials paints a cooler picture.
What the evidence actually shows
Vitamin c is not a silver bullet against the common cold. Decades of controlled studies suggest a modest benefit only when taken regularly before you fall ill, and very little impact if you start at the first sneeze.
When taken daily, around 200–500 mg of vitamin c can slightly reduce how long and how hard a cold hits. Starting it after symptoms begin rarely changes the course.
Meta-analyses report small but measurable effects. In adults, routine vitamin c cut cold duration by roughly 8%; in children, by about 14%. Symptom intensity dips a little too. These averages hide big individual variation, which explains why some people swear by it while others notice nothing.
Where it seems to make a real difference
There is one standout group. People under sustained, heavy physical stress in cold conditions—think endurance athletes and military recruits—show far fewer colds when taking vitamin c daily. In several trials, the risk of catching a cold was roughly halved in these settings. For most of us, though, incidence doesn’t budge much.
If you’re already ill: will vitamin c help?
Starting vitamin c once your nose is blocked and your throat raspy offers little to no benefit. Multiple trials find no meaningful change in duration or severity when begun after symptoms appear. You might still feel comforted by the ritual; the infection itself will run its course.
For treatment, timing is everything—and the window seems to be before you’re ill, not after symptoms start.
Dose, safety and the line you shouldn’t cross
In the UK, adults generally need about 40 mg of vitamin c a day, easily met by normal food. Many supplements deliver 200–500 mg; that range is where prevention data mostly sit. Mega-doses are a different story.
More is not better: above about 2 g per day, the odds of unpleasant effects rise without extra benefits.
High intakes can trigger diarrhoea, stomach cramps, acid reflux and nausea. In people predisposed to kidney stones, frequent high doses may increase risk. Vitamin c also enhances iron absorption, which is unhelpful for those with iron overload conditions. If you take prescription medicines or have a history of stones, ask a clinician before supplementing heavily.
- Reasonable daily target for prevention during high-exposure weeks: 200–500 mg
- Avoid routine intakes above 2,000 mg per day
- Split doses with food if you’re sensitive to stomach upset
- Stop if you notice persistent gut symptoms
What to try when a cold actually hits
Once a cold is underway, supportive measures matter more than vitamin c. These options carry better evidence for shortening misery or easing symptoms:
- Zinc lozenges taken within 24 hours of onset may trim duration, especially if the total daily elemental zinc is around 75 mg. Expect a metallic taste and occasional nausea.
- Fluids and rest help your immune system clear the virus efficiently.
- Saline nasal rinses can decongest without rebound effects.
- Honey at bedtime can soothe coughs in adults and older children.
- Paracetamol or ibuprofen can manage fever and aches when needed.
- Vitamin d helps if you’re deficient; routine megadoses bring no quick fix.
- Some probiotics show small benefits in reducing respiratory infections across a season.
Food first: easy ways to reach effective intakes
A varied diet covers most people’s needs and provides other helpful compounds. You can hit preventive levels without a single tablet if you plan a little.
| Food | Typical portion | Vitamin c (approx.) |
|---|---|---|
| Red pepper | 1/2 large (75 g) | 100–120 mg |
| Kiwi | 1 medium | 70–80 mg |
| Strawberries | 1 cup (150 g) | 80–90 mg |
| Orange | 1 medium | 60–70 mg |
| Broccoli (steamed) | 1 portion (80 g) | 40–50 mg |
Two simple meals can cover you: a pepper-and-broccoli stir-fry at lunch and a kiwi or orange at tea time. That puts you squarely in the 200–300 mg range without effervescence.
Prevention versus treatment at a glance
| Goal | What vitamin c can do | What to consider |
|---|---|---|
| Prevent colds | Slightly fewer symptoms and shorter duration with daily use | 200–500 mg/day; bigger impact if you face heavy physical stress |
| Treat a cold | Little to no benefit when started after onset | Focus on zinc (early), rest, fluids, saline, and symptom relief |
| Athletes in cold | Lower chance of catching a cold with daily use | Consider a seasonal course during intense training blocks |
How to apply this without wasting money
Decide your aim. If you want a small nudge on duration over the season, choose a modest daily dose and build meals around rich produce. If you only act when you feel rough, direct your budget towards zinc lozenges for day one, tissues and time off.
Think of vitamin c as a gentle seasonal insurance, not an emergency fire extinguisher.
Practical extras you might not have considered
Track your own pattern. Over one winter, note dates and duration of colds with and without daily vitamin c. Personal data beats anecdotes and helps you judge if a routine supplement is worth it for you.
Be mindful of context. If you have a history of kidney stones, iron overload, or take medicines affected by acidity, speak to a healthcare professional before high-dose regimens. Store tablets away from humidity to preserve potency, and avoid “time‑release” claims that encourage overshooting sensible doses.
For parents, food sources work well and are safer than large tablets. A lunchbox with strawberries and peppers can cover a child’s daily needs comfortably, while keeping the focus on a balanced plate.
Are we basicaly paying £15 for fancy fizz when 200–500 mg would do?