Ask anyone what vitamin C is for and they will say colds. Ironically, that is the claim with the weakest evidence. The better-supported vitamin C benefits are less famous: your body cannot make collagen properly without it, it protects cells from oxidative damage, and it can significantly increase how much iron you absorb from plant foods. Most people can get enough from food, and megadoses add little.
Here is what vitamin C does well, where the hype outruns the science, and how to get enough without overthinking it.
Key takeaways
- Adults need about 75–90 mg of vitamin C a day according to the NIH, plus 35 mg extra for smokers. One guava or a red capsicum covers it.
- Vitamin C is essential for building collagen; that is why severe deficiency (scurvy) causes bleeding gums and poor wound healing.
- Taking vitamin C with a meal can markedly improve absorption of non-haem iron from plant foods. Tea with meals does the opposite.
- A Cochrane review found regular vitamin C does not prevent colds in most people, though it may shorten them slightly.
- Absorption drops sharply above about 1 g a day, and high-dose supplements are linked to kidney stones in men.
What does vitamin C actually do?
Vitamin C (ascorbic acid) is a water-soluble vitamin that humans, unlike most animals, cannot make. We lost the enzyme needed to produce it somewhere in our evolutionary past, so it has to come from food.
It has three big jobs. It is an antioxidant, helping neutralise reactive molecules that damage cells. It is a cofactor for enzymes that build and stabilise collagen, the protein that holds together skin, blood vessels, tendons and gums. And it helps the body absorb iron from plant sources. It also plays a role in immune cell function, which is where the cold story began.
What are the main vitamin C benefits for skin?
This is where the collagen connection matters. Enzymes called prolyl and lysyl hydroxylases need vitamin C to fold and cross-link collagen fibres properly. Without it, collagen is weak and unstable. Scurvy shows this in extreme form: the NIH notes symptoms can appear after about a month of very low intake, starting with fatigue and progressing to bleeding gums, easy bruising and wounds that will not heal.
What about the rest of us, who are not deficient? Observational research is encouraging but not proof. A 2007 study in the American Journal of Clinical Nutrition, using data from over 4,000 US women aged 40–74, found that higher dietary vitamin C intake was associated with a lower likelihood of a wrinkled appearance and skin dryness, after accounting for age, sun exposure and other factors. People who eat more fruit and vegetables tend to differ in other ways too, so it does not prove vitamin C caused the difference.
If you are taking collagen supplements, it makes sense to cover your vitamin C, since collagen synthesis depends on it. We looked at the collagen evidence in detail in our no-nonsense guide to collagen supplements.
Oral or topical vitamin C?
They do different jobs. Oral vitamin C supports collagen production throughout the body but does not concentrate dramatically in skin once your levels are adequate. Topical serums deliver vitamin C directly to the skin, and according to Oregon State University's Linus Pauling Institute, L-ascorbic acid needs a concentration of around 10–20% and an acidic pH (below about 3.5) to penetrate well. It is unstable, which is why serums turn orange as they oxidise; store them away from light and heat, and toss them once they darken. Formulas combining vitamin C with vitamin E and ferulic acid are more stable and add some protection against UV damage. They complement sunscreen; they do not replace it.
How does vitamin C help iron absorption?
This is the most practical and least appreciated benefit. There are two types of dietary iron. Haem iron, from meat, poultry and fish, is absorbed fairly well. Non-haem iron, from beans, tofu, leafy greens, lentils and fortified cereals, is absorbed much less efficiently.
Vitamin C helps by converting non-haem iron into a more absorbable form and keeping it soluble in the gut. The NIH notes that vitamin C and meat both enhance non-haem iron absorption, while polyphenols in tea and coffee, calcium, and phytates in whole grains and legumes reduce it. In single-meal studies, adding vitamin C can increase non-haem iron absorption several-fold; over longer periods the effect is smaller but still useful for people who rely on plant foods.
This matters in Malaysia, where iron deficiency anaemia remains common among women of reproductive age, and where many of us drink tea with meals. Your teh tarik alongside nasi lemak is working against the iron on your plate. (It is also carrying a fair amount of sugar, as we found in our look at Malaysia's favourite drinks.)
Simple swaps that help:
- Add a vitamin C source to plant-iron meals: tomato and capsicum with tofu or dhal, a squeeze of lime on kangkung, a slice of guava or papaya after lunch.
- Move tea and coffee to between meals, ideally an hour or so away from your main iron-rich meal.
Does vitamin C prevent colds?
For most people, no. A 2013 Cochrane review by Harri Hemilä and Elizabeth Chalker pooled 29 trials with over 11,000 participants and found regular vitamin C supplementation did not reduce how often people caught colds. It did modestly shorten them: by about 8% in adults and 14% in children, or roughly half a day for a typical week-long cold.
The exception was people under heavy short-term physical stress, such as marathon runners, skiers and soldiers in subarctic conditions, whose risk of catching a cold was roughly halved. Taking vitamin C only after symptoms start showed no consistent benefit. Zinc lozenges have somewhat better evidence for shortening colds; we covered that in our guide to zinc.
How much vitamin C do you need, and where do you get it?
The NIH recommends 90 mg a day for men and 75 mg for women, with an extra 35 mg for smokers. The upper limit is 2,000 mg a day; above this, diarrhoea and stomach upset are common.
| Food | Approx. vitamin C |
|---|---|
| Guava (jambu batu), 100 g | ~228 mg |
| Red capsicum, raw, half a cup | ~95 mg |
| Orange, 1 medium | ~70 mg |
| Kiwifruit, 1 medium | ~64 mg |
| Papaya, 100 g | ~60 mg |
| Broccoli, cooked, half a cup | ~51 mg |
| Strawberries, half a cup | ~49 mg |
Vitamin C is destroyed by heat and leaches into cooking water, so steaming, stir-frying briefly or eating produce raw preserves more than long boiling.
Your body absorbs 70–90% of vitamin C at typical intakes, but absorption falls below 50% above about 1 g a day, and the excess is excreted. In other words, a 1,000 mg tablet is mostly expensive urine. If you want a convenient daily top-up, THRIVE combines vitamin C with iron, zinc and a greens blend in one effervescent tablet, which suits the iron-plus-vitamin-C pairing described above. It works alongside fruit and vegetables, not instead of them.
Who should be careful with high doses?
- Men prone to kidney stones: a large Swedish cohort study found men taking vitamin C supplements had about twice the risk of kidney stones as non-users.
- People with haemochromatosis (iron overload), since vitamin C increases iron absorption.
- People having medical tests: high doses can interfere with some blood glucose and stool tests. Tell your doctor what you take.
- People undergoing cancer treatment should discuss any antioxidant supplements with their oncology team.
This article is general information, not medical advice. Talk to a doctor or pharmacist before starting supplements, especially if you are pregnant, take medication or are managing a health condition.
Frequently asked questions
Is it better to get vitamin C from food or supplements?
Food first. Fruit and vegetables provide vitamin C along with fibre, potassium and other beneficial compounds, and one or two servings usually cover your daily needs. Supplements are a convenient backup if your diet is limited, but high doses add little benefit.
Can you take too much vitamin C?
Yes. The upper limit for adults is 2,000 mg a day. Above this, diarrhoea, nausea and stomach cramps are common, and long-term high-dose use is linked to kidney stones in some people, particularly men.
Should I take vitamin C with iron supplements?
Taking vitamin C with iron can help absorption of non-haem iron, and it is a common pairing. Avoid taking iron with tea, coffee or calcium supplements, which reduce absorption. Follow your doctor's advice if you are being treated for anaemia.
Does vitamin C help with dark spots?
Topical vitamin C has some evidence for gradually improving uneven pigmentation and protecting against UV-related damage. Results are modest and take weeks to months. Daily sunscreen remains the most important step for preventing dark spots.
What time of day should I take vitamin C?
Timing matters less than consistency. Taking it with a meal can reduce stomach upset and helps with iron absorption from that meal. Splitting larger amounts across the day is absorbed more efficiently than one big dose.
Sources
- NIH Office of Dietary Supplements — Vitamin C: Fact Sheet for Health Professionals
- NIH Office of Dietary Supplements — Iron: Fact Sheet for Health Professionals
- Linus Pauling Institute, Oregon State University — Vitamin C
- Linus Pauling Institute — Vitamin C and Skin Health
- Hemilä & Chalker (2013), Vitamin C for preventing and treating the common cold, Cochrane Database of Systematic Reviews (PubMed)
- NHS — Vitamin C
