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What vitamin C does
Vitamin C (ascorbic acid) is a water-soluble vitamin humans can't make, so it has to come from food. The body needs it to build collagen (for skin, blood vessels, gums and wound healing), to absorb iron from plant foods, and as an antioxidant. It also supports immune cells.
Severe deficiency causes scurvy: bleeding gums, easy bruising, poor wound healing and fatigue. Scurvy is rare, but low vitamin C levels are common, especially in older adults with limited diets.
Absorption is capped. In a careful NIH study, a single 200 mg dose was fully absorbed, but at 500 mg and above the body absorbed a smaller share and excreted the extra in urine. Blood levels level off at a few hundred milligrams a day, however much more you take. [1]
Clinical evidence — what the trials show
| Study | What was tested | Design | Key finding | Grade |
|---|---|---|---|---|
| Hemilä & Chalker (2013) — Cochrane Review doi:10.1002/14651858.CD000980.pub4 |
Regular vitamin C (≥200 mg/day) and treatment at cold onset | Systematic review | Daily vitamin C didn't reduce how many colds ordinary people caught (29 comparisons, 11,306 people). It shortened colds by 8% in adults and 14% in children. Taking it only once symptoms started showed no consistent benefit. | A |
| Same review — physically stressed groups | Marathon runners, skiers, soldiers in subarctic exercises | 5 trials, n = 598 | Vitamin C roughly halved the risk of catching a cold (risk ratio 0.48). | A |
| Levine et al. (1996) — PNAS doi:10.1073/pnas.93.8.3704 |
30–2,500 mg/day, inpatient study | Pharmacokinetic study, n = 7 | 200 mg was fully absorbed. At 500 mg and above, absorption fell and the excess was excreted. | A |
| Thomas et al. (2013) — JAMA Intern Med doi:10.1001/jamainternmed.2013.2296 |
Vitamin C supplement use | Cohort, Swedish men, 11 years | Users of vitamin C supplements had about twice the risk of kidney stones. Multivitamins, which contain less vitamin C, showed no link. | B |
How much you need
Evidence-based protocol
Daily need: ICMR-NIN 2020 sets 80 mg/day for men and 65 mg/day for women. [5] If you supplement: 200–500 mg a day covers everything the evidence supports. More than that is mostly excreted. [1] For colds: the modest benefit comes from taking it daily, not from starting when you feel ill. [2] Upper limit: 2,000 mg/day for adults; above that, diarrhoea and stomach upset become common. [6]
Food first. Amla, guava, oranges, lemon, bell peppers, tomatoes and green leafy vegetables are rich sources. An amla or a guava alone can cover a day's need. Vitamin C is destroyed by long cooking, so raw or lightly cooked sources count most.
India-specific context
Cheap in food, yet common deficiency
Deficiency in older Indians is a real problem: nearly three in four adults over 60 in the north Indian study were deficient. [4] Those most at risk are older adults, people with limited diets, smokers, and people who eat little fresh fruit or raw vegetables. Vitamin C also improves iron absorption from plant foods, which matters in a largely vegetarian country with high rates of anaemia. See our iron deep-dive.
Indian brand comparison
| Product | Price | Dose | Score | Our take |
|---|---|---|---|---|
| Wellbeing Nutrition Vitamin C Melts | ₹599 / 30 days | 500 mg ascorbic acid | 6.6 (C) | A sensible dose. The dissolving strip adds convenience but little absorption, since vitamin C isn't absorbed through the mouth. |
| Himalayan Organics Vitamin C 1000 mg | ₹499 / 90ct | 1,000 mg ascorbic acid | 6.4 (C) | Clean single ingredient, but more than you can absorb in one dose. Splitting the tablet halves the cost. No COA. |
| Himalayan Organics Collagen Builder Vitamin C | ₹499 / 60ct | Vitamin C with amla | 5.8 (D) | Marketed for collagen, but it's a vitamin C supplement, not a collagen supplement. |
Scores and prices come from our product database (2026). A plain, cheap ascorbic acid tablet is all most people need, if they need one at all.
Safety
Kidney stones
Part of excess vitamin C is turned into oxalate, a component of the most common kidney stones. Men taking vitamin C supplements had about twice the risk in a large Swedish study. [3] If you've had kidney stones, avoid high-dose supplements.
Stomach upset at high doses
Above about 2,000 mg a day, diarrhoea, cramps and nausea are common. That's why the upper limit is set there. [6]
Iron overload
Because vitamin C increases iron absorption, people with haemochromatosis or thalassaemia on transfusions should only take it on medical advice.
Can interfere with some tests
High doses can affect some lab and glucose-meter readings. Tell your doctor or lab if you take gram doses.
Commonly taken together
Iron (plant sources)
High synergyVitamin C in the same meal improves absorption of iron from plant foods. With iron tablets, though, a separate vitamin C pill didn't add much in trials. See the iron deep-dive.
Zinc
ModerateOften paired for colds. Each has separate evidence; neither is a cure. See our zinc deep-dive.
Collagen
ModerateVitamin C is needed to make collagen, so it's often added to collagen products. Most people already get enough from food.
Vitamin D3
Different roleBoth are sold for immunity. In India, vitamin D deficiency is far more common and more consequential. See our vitamin D3 deep-dive.
Scoring rubric — full breakdown
1. Evidence quality
A large Cochrane review gives a clear, modest answer on colds, and deficiency correction is well established. We deduct because the popular uses (preventing colds, treating them at onset) aren't supported. [2]
2. Dosage confidence
Absorption and plateau data make it clear that 200–500 mg covers the benefit, and the RDA and upper limit are well defined. [1][5][6]
3. India market fit
Deficiency is common in older adults, and vitamin C helps iron absorption in a mostly vegetarian country. But cheap foods like amla make supplements unnecessary for most people. [4]
4. Safety profile
Very safe at normal doses. We deduct for the kidney-stone link with supplements in men and stomach upset at gram doses. [3]
5. Label accuracy (tested)
Simple ingredient, clearly labelled, but few brands publish COAs, and some products overstate their format or purpose. [7]
References
- 1Levine M, et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci USA. 1996;93(8):3704–9.doi:10.1073/pnas.93.8.3704
- 2Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;CD000980.doi:10.1002/14651858.CD000980.pub4
- 3Thomas LDK, et al. Ascorbic acid supplements and kidney stone incidence among men: a prospective study. JAMA Intern Med. 2013.doi:10.1001/jamainternmed.2013.2296
- 4Ravindran RD, et al. Prevalence and risk factors for vitamin C deficiency in north and south India: a two centre population based study in people aged 60 years and over. PLoS One. 2011;6(12):e28588.doi:10.1371/journal.pone.0028588
- 5ICMR–National Institute of Nutrition. Nutrient Requirements for Indians: Recommended Dietary Allowances and Estimated Average Requirements. Hyderabad: ICMR-NIN; 2020.
- 6NIH Office of Dietary Supplements. Vitamin C — Health Professional Fact Sheet (tolerable upper intake level). ods.od.nih.gov
- 7Naked Compound product database (2026): vitamin C products, prices and scores.
Medical note. This page is educational and not a diagnosis. See a doctor for bleeding gums, easy bruising or wounds that won't heal, which can signal deficiency or another condition.
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