Short answer. Adults need 75 to 90 mg of vitamin C a day and children aged 1 to 13 need 15 to 45 mg, according to the NIH Office of Dietary Supplements. One orange gives about 70 mg. The upper limit is 2,000 mg for adults and 400 mg for toddlers, and above 1 gram a day the body absorbs less than half.
Vitamin C forms at a glance
| Form | What the research shows | What to know |
|---|---|---|
| Ascorbic acid (synthetic or from food) | Chemically identical to the vitamin C in fruit; every steady-state human comparison found no difference in bioavailability | The most common and least expensive form |
| Mineral ascorbates (sodium, calcium, magnesium) | The same vitamin C bound to a mineral; a common supplement form | Each one adds its mineral to the day's total |
| Ester-C (calcium ascorbate with vitamin C metabolites) | In 36 adults, 1,000 mg gave the same plasma levels as ascorbic acid, with a higher white-cell level at 24 hours | Single-dose studies; another study found no difference in plasma or urine |
| Liposomal vitamin C | In 27 adults, 500 mg raised peak plasma levels 27% more than standard vitamin C | Formulations vary widely; long-term data are limited |
Source: NIH Office of Dietary Supplements; Carr 2013 (PMID 24169506); Mitmesser 2016 (PMID 27512620); Purpura 2024 (PMID 39237620).
What does vitamin C do in the body?
Vitamin C, also called L-ascorbic acid, is a water-soluble vitamin. Most animals make their own, but humans cannot, so it has to come from food or supplements every day (NIH Office of Dietary Supplements).
The body uses it to build collagen, the protein in connective tissue that holds skin, blood vessels, gums and cartilage together and that plays a vital role in wound healing. It is also needed to make L-carnitine and certain neurotransmitters, and it takes part in protein metabolism. Vitamin C is an important antioxidant in the body and can regenerate other antioxidants, including vitamin E. It plays a role in normal immune function and improves the absorption of nonheme iron, the form found in plant foods (NIH Office of Dietary Supplements).
How much vitamin C do children and adults need?
The Recommended Dietary Allowance (RDA) covers the needs of nearly all healthy people. The upper limit (UL) covers food and supplements combined.
| Age | Boys and men | Girls and women | Upper limit |
|---|---|---|---|
| 0–6 months | 40 mg (Adequate Intake) | 40 mg (Adequate Intake) | Not established |
| 7–12 months | 50 mg (Adequate Intake) | 50 mg (Adequate Intake) | Not established |
| 1–3 years | 15 mg | 15 mg | 400 mg |
| 4–8 years | 25 mg | 25 mg | 650 mg |
| 9–13 years | 45 mg | 45 mg | 1,200 mg |
| 14–18 years | 75 mg | 65 mg | 1,800 mg |
| 19 years and older | 90 mg | 75 mg | 2,000 mg |
| Pregnancy | — | 80 mg (14–18), 85 mg (19+) | 1,800 mg (14–18), 2,000 mg (19+) |
| Lactation | — | 115 mg (14–18), 120 mg (19+) | 1,800 mg (14–18), 2,000 mg (19+) |
Source: NIH Office of Dietary Supplements.
People who smoke need 35 mg more per day than people who do not. For infants, breast milk or formula and food should be the only sources of vitamin C. The Daily Value on labels is 90 mg for adults and children 4 and older. A child's supplement dose is a question for the pediatrician.
Vitamin C in common foods
| Food and serving | Vitamin C, mg |
|---|---|
| Red bell pepper, raw, ½ cup | 95 |
| Orange juice, ¾ cup | 93 |
| Orange, 1 medium | 70 |
| Kiwifruit, 1 medium | 64 |
| Green bell pepper, raw, ½ cup | 60 |
| Broccoli, cooked, ½ cup | 51 |
| Strawberries, sliced, ½ cup | 49 |
| Brussels sprouts, cooked, ½ cup | 48 |
| Potato, baked, 1 medium | 17 |
Source: NIH Office of Dietary Supplements.
Five varied servings of fruits and vegetables a day can provide more than 200 mg. Heat and long storage destroy vitamin C; steaming or microwaving keeps more of it (NIH Office of Dietary Supplements). In US surveys, average food intakes were 105.2 mg a day for men and 83.6 mg for women, so most people already meet the RDA.
Does taking more vitamin C mean the body gets more?
Only up to a point. Absorption depends on a transporter in the gut that saturates. About 70% to 90% of vitamin C is absorbed at intakes of 30 to 180 mg a day, but above 1 gram a day absorption falls to less than 50%, and the extra is passed in urine (NIH Office of Dietary Supplements).
The clearest data come from an NIH study in which 7 healthy volunteers lived in hospital for 4 to 6 months on a diet with less than 5 mg of vitamin C a day, then received doses from 30 to 2,500 mg. Blood levels rose steeply between 30 and 100 mg a day and were fully saturated at 1,000 mg. A single 200 mg dose was completely absorbed, while at single doses of 500 mg and more, absorption declined and the absorbed extra went out in urine (Levine 1996).
Modeling cited by the NIH suggests that even 3 g every 4 hours would raise peak blood levels to only 220 micromoles per liter, compared with 135 micromoles per liter from 1.25 g a day.
Who is most likely to run low on vitamin C?
True deficiency is rare in the US. In the 2003–2004 national survey of 7,277 people aged 6 and older, 7.1% had a deficient blood level (below 11.4 micromoles per liter). Adult smokers had levels about one-third lower than nonsmokers, and low income raised the risk (Schleicher 2009).
The NIH lists these groups as more likely to fall short of the RDA:
- People who smoke and people exposed to secondhand smoke. Their blood and white-cell levels are lower, partly because of extra oxidative stress.
- Infants fed evaporated or boiled cow's milk. Cow's milk has very little vitamin C and heat destroys what is there; breast milk and infant formula supply enough.
- People who eat a narrow range of foods, including some older adults who cook for themselves and, occasionally, children with very limited diets.
- People with severe intestinal malabsorption or on long-term hemodialysis.
When intake stays below about 10 mg a day, signs can appear within a month: tiredness, inflamed or bleeding gums, small red spots and easy bruising on the skin, joint pain, slow wound healing and corkscrew-shaped hairs (NIH Office of Dietary Supplements). These are reasons to talk with a doctor and review the diet, not to self-diagnose. A blood test mostly reflects recent intake.
Which form of vitamin C is best?
Natural and synthetic vitamin C are the same molecule. A review found that every steady-state comparison in humans showed no difference in bioavailability between them (Carr 2013), and the NIH states that ascorbic acid in supplements is as bioavailable as the vitamin C in orange juice and broccoli. Vitamin C from acerola or rose hips is still ascorbic acid. For daily needs, plain ascorbic acid works and costs the least; the other forms differ mainly in what comes with the vitamin C and in blood levels after a single dose.
- Buffered mineral ascorbates (sodium, calcium or magnesium ascorbate) carry the same vitamin C. They also add their mineral, which counts toward the day's sodium, calcium or magnesium.
- Ester-C is calcium ascorbate with vitamin C metabolites. In a crossover trial of 36 adults given 1,000 mg, plasma levels did not differ from ascorbic acid, but the white-cell vitamin C level rose more by 24 hours (Mitmesser 2016). Another comparison found no difference among ascorbic acid, Ester-C and ascorbic acid with bioflavonoids (NIH Office of Dietary Supplements).
- Liposomal vitamin C is wrapped in fat-based bubbles. In a crossover trial of 27 adults, 500 mg of a liposomal form raised peak plasma vitamin C 27% and peak white-cell vitamin C 20% more than 500 mg of standard vitamin C (Purpura 2024). A 2025 scoping review found higher blood levels with liposomal forms in 9 of 10 studies, but the products and doses varied widely and no study measured urinary loss (Carr 2025).
All of these studies looked at blood levels after one dose, not at long-term outcomes.
Can you take too much vitamin C?
Vitamin C has low toxicity. The most common problems with high doses are diarrhea, nausea and abdominal cramps, caused by unabsorbed vitamin C pulling water into the gut. That is the reason for the upper limits in the table (NIH Office of Dietary Supplements).
Two cautions apply to specific people. High intakes can raise oxalate and uric acid in urine; studies on kidney stones have conflicting results, and the best evidence of a link is in people who already have high urine oxalate. In the NIH study, oxalate and urate excretion were higher at 1,000 mg a day (Levine 1996). And because vitamin C increases iron absorption, people with inherited iron overload (hemochromatosis) are advised to avoid vitamin C supplements; in healthy people extra iron absorption does not appear to be a concern (NIH Office of Dietary Supplements).
Should you take vitamin C with iron?
For plant-based iron, yes. Vitamin C helps the gut absorb nonheme iron from food and supplements. In a trial in 34 women with low iron stores, taking 100 mg of iron with 80 mg of vitamin C raised iron absorption by 30%; a 500 mg dose of vitamin C added nothing more. Coffee cut absorption by 54% (von Siebenthal 2023). There is more on timing in our article on iron.
Does vitamin C interact with medicines?
The NIH lists these:
- Chemotherapy drugs and radiation therapy. Antioxidants might change how drugs such as cyclophosphamide and doxorubicin, and radiation, act on the cells they target. Anyone receiving these should ask the doctor managing them before taking vitamin C or other antioxidants, especially in high doses.
- Simvastatin with niacin (Zocor plus niacin). Vitamin C together with other antioxidants may blunt the rise in HDL cholesterol from this combination; the prescriber may want to monitor lipid levels.
Which ASDHelp products contain vitamin C?
Doses are copied from each label. Add up the vitamin C from every product and fortified food and compare it with the upper limit for each person's age.
- Spectrum C: 600 mg per capsule, as ascorbic acid and acerola, with citrus bioflavonoids, rutin and quercetin. Label directions: 1 capsule a day; the capsule can be opened into food or a drink; no children's dose. One capsule is above the 400 mg upper limit for ages 1 to 3.
- Formula C: 500 mg per 6 capsules, as L-ascorbic acid, inside a multivitamin-mineral. Label directions: adults and children 4 years or older, 6 capsules daily with food; under 4, as directed by a healthcare professional.
- Spectrum Formula Advance: 300 mg per scoop (about 5.2 g), as L-ascorbic acid, inside a multivitamin powder. Label directions: adults, 1 scoop daily with food or a drink; children as directed by a healthcare professional.
- Spectrum Formula Chewable + Iron: 250 mg per 4 chewable tablets, as ascorbic acid, with 3 mg of iron. Label directions: children 1 to 3 years, one to two tablets twice daily; 4 years or more, two to four tablets twice daily. The top label use stays below the upper limit for each age.
- MITOboost Protein Powder Strawberry: 250 mg per scoop (29.6 g), as calcium ascorbate. Label directions: 1 scoop once daily; no children's dose.
- Spectrum Electrolytes: 1,734 mg per 8 g scoop, as ascorbic acid, calcium ascorbate and magnesium ascorbate, with 80 mg of magnesium. Label directions: one scoop in 10 to 12 ounces of water a day; no children's dose. One scoop is above the upper limit for every age through 13 and close to the limit for teens and adults.
Questions to take to your doctor
- Does our diet already cover the RDA for each person's age, and is a supplement needed at all?
- If a supplement makes sense, what dose and which form, and is any of our products above the upper limit for a child's age?
- Given any history of kidney stones or iron overload in the family, should we keep vitamin C supplements low?
- Do any of our medicines or upcoming treatments call for avoiding antioxidant supplements?
Sources
- NIH Office of Dietary Supplements. Vitamin C fact sheet for health professionals. ods.od.nih.gov
- NIH Office of Dietary Supplements. Iron fact sheet for health professionals. ods.od.nih.gov
- National Academies. Dietary Reference Intakes tables (NCBI Bookshelf). ncbi.nlm.nih.gov/books/NBK545442
- Levine M et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci U S A 1996. PMID 8623000
- Carr AC, Vissers MC. Synthetic or food-derived vitamin C: are they equally bioavailable? Nutrients 2013. PMID 24169506
- Schleicher RL et al. Serum vitamin C and the prevalence of vitamin C deficiency in the United States: 2003–2004 NHANES. Am J Clin Nutr 2009. PMID 19675106
- Mitmesser SH et al. Determination of plasma and leukocyte vitamin C concentrations in a randomized, double-blind, placebo-controlled trial with Ester-C. Springerplus 2016. PMID 27512620
- Purpura M et al. Liposomal delivery enhances absorption of vitamin C into plasma and leukocytes: a double-blind, placebo-controlled, randomized trial. Eur J Nutr 2024. PMID 39237620
- Carr AC. Do liposomal vitamin C formulations have improved bioavailability? A scoping review. Basic Clin Pharmacol Toxicol 2025. PMID 40506693
- von Siebenthal HK et al. Effect of dietary factors and time of day on iron absorption from oral iron supplements in iron deficient women. Am J Hematol 2023. PMID 37357807
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is educational and is not medical advice.