Evidence-based·Last reviewed May 31, 2026·How we grade evidence

Vitamin C (ascorbic acid)

VitaminL-ascorbic acid

An essential water-soluble vitamin needed for collagen synthesis, immune function, and non-heme iron absorption. Reliably prevents and treats scurvy; modestly shortens cold duration when taken daily; doesn't prevent colds in the general population.

Quick decision guide

May help most

Preventing or correcting scurvy, improving non-heme iron absorption from plant foods, and possibly shortening colds when taken daily long-term.

Common dosing range

75–200 mg/day for general supplementation; up to 1,000–2,000 mg/day short-term for cold or iron-absorption use.

When to expect effects

Days for scurvy reversal; weeks of regular use for cold-duration benefit.

Watch out for

Doses above 2,000 mg/day commonly cause diarrhea, and chronic high doses may increase kidney stone risk in susceptible people.

Evidence snapshot

Scurvy prevention and treatmentStrong

Non-heme iron absorptionStrong

Common cold duration (regular use)Moderate

Cold incidence (general population)Low

Cardiovascular and cancer preventionLow

What is it

Ascorbic acid is the chemical name for vitamin C, the water-soluble vitamin essential for collagen synthesis, antioxidant defense, and immune function. It is the most common form found in supplements.

Is it worth it for you?

Use this as a quick fit check, not a diagnosis.

Worth considering if…

Your diet is low in fresh fruits and vegetables (especially citrus, peppers, kiwi, berries)

You smoke, which raises your daily requirement by 35 mg/day

You're treating iron-deficiency anemia and taking non-heme iron from plant sources or supplements

You're an endurance athlete or face frequent extreme physical stress (marathon, military training, cold exposure)

You want a modest reduction in cold duration with daily, long-term use

Probably skip if…

You already eat varied produce daily and just want 'extra immunity' — daily megadoses don't prevent colds in most adults

You're hoping to prevent or cure cancer with high-dose oral vitamin C — no consistent clinical-trial benefit

You have hemochromatosis or another iron-overload disorder — high vitamin C boosts iron absorption

You're prone to oxalate kidney stones and considering chronic doses >1,000 mg/day

You're on chemotherapy without first clearing it with your oncologist

Evidence at a glance

Goal	Effect	Best fit	Time
Scurvy prevention and treatment Strong Evidence	Symptom reversal within 1–2 weeks at 100–300 mg/day; the RDA of 75–90 mg/day prevents recurrence indefinitely	Adults with restricted produce intake, alcohol use disorder, severe eating disorders, food insecurity, or rare malabsorption	Days to 2 weeks
Non-heme iron absorption Strong Evidence	2–3× single-meal non-heme iron uptake at 25–100 mg vitamin C; modest (~0.14 g/dL) hemoglobin gain over iron alone in IDA	Vegetarians, vegans, premenopausal women with low iron stores, anyone treating iron-deficiency anemia with non-heme iron supplements	Single meal for absorption; weeks–months for hemoglobin change
Common cold duration (regular daily use) Good Evidence	8% shorter colds in adults / 14% in children with daily ≥200 mg; no incidence reduction in non-athletes	People who can commit to daily intake well before cold season; endurance athletes; soldiers in cold conditions	Weeks (must be taken regularly before infection)
Cardiovascular disease prevention Limited Evidence	No consistent reduction in CV events from supplementation in long-term RCTs	People who can replace supplements with daily fruit/vegetable intake	Not established for supplementation
Cancer prevention Mixed Evidence	No consistent oral-supplement effect; IV vitamin C is investigational and separate	Research participants in IV vitamin C oncology trials under medical supervision	Not established

Scurvy prevention and treatment

Strong Evidence

Effect: Symptom reversal within 1–2 weeks at 100–300 mg/day; the RDA of 75–90 mg/day prevents recurrence indefinitely
Best fit: Adults with restricted produce intake, alcohol use disorder, severe eating disorders, food insecurity, or rare malabsorption
Time: Days to 2 weeks

Non-heme iron absorption

Strong Evidence

Effect: 2–3× single-meal non-heme iron uptake at 25–100 mg vitamin C; modest (~0.14 g/dL) hemoglobin gain over iron alone in IDA
Best fit: Vegetarians, vegans, premenopausal women with low iron stores, anyone treating iron-deficiency anemia with non-heme iron supplements
Time: Single meal for absorption; weeks–months for hemoglobin change

Common cold duration (regular daily use)

Good Evidence

Effect: 8% shorter colds in adults / 14% in children with daily ≥200 mg; no incidence reduction in non-athletes
Best fit: People who can commit to daily intake well before cold season; endurance athletes; soldiers in cold conditions
Time: Weeks (must be taken regularly before infection)

Cardiovascular disease prevention

Limited Evidence

Effect: No consistent reduction in CV events from supplementation in long-term RCTs
Best fit: People who can replace supplements with daily fruit/vegetable intake
Time: Not established for supplementation

Cancer prevention

Mixed Evidence

Effect: No consistent oral-supplement effect; IV vitamin C is investigational and separate
Best fit: Research participants in IV vitamin C oncology trials under medical supervision
Time: Not established

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Scurvy prevention and treatment

Corrects deficiency

Strong Evidence

Vitamin C is the proximate cure for scurvy, a deficiency disease caused by intake below ~10 mg/day for several weeks. Symptoms (gum bleeding, fatigue, poor wound healing, perifollicular hemorrhage) reverse within days at typical adult doses. Scurvy is rare in the general population but appears in alcohol use disorder, restrictive eating, severe food insecurity, and some psychiatric or autistic patients with very limited diets.

Effect size

Symptom reversal within 1–2 weeks at 100–300 mg/day; the RDA of 75–90 mg/day prevents recurrence indefinitely

Time to effect

Days to 2 weeks

Best fit

Adults with restricted produce intake, alcohol use disorder, severe eating disorders, food insecurity, or rare malabsorption

Less likely

Adults eating any varied diet with fruits and vegetables — frank scurvy is rare

Bottom line: Definitive: vitamin C cures scurvy. Make sure intake stays ≥75–90 mg/day from food or supplements.

SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

Non-heme iron absorption

Supplement benefit

Strong Evidence

Ascorbic acid reduces dietary ferric iron (Fe³⁺) to the absorbable ferrous form (Fe²⁺) and forms a soluble complex that survives the alkaline duodenum. Single-meal studies consistently show 2–3× increases in non-heme iron uptake. Long-term effects on hemoglobin and ferritin are smaller — a 2023 meta-analysis found adding vitamin C to iron supplements raised hemoglobin by only ~0.14 g/dL above iron alone in iron-deficient adults.

Effect size

2–3× single-meal non-heme iron uptake at 25–100 mg vitamin C; modest (~0.14 g/dL) hemoglobin gain over iron alone in IDA

Time to effect

Single meal for absorption; weeks–months for hemoglobin change

Best fit

Vegetarians, vegans, premenopausal women with low iron stores, anyone treating iron-deficiency anemia with non-heme iron supplements

Less likely

People with hemochromatosis or iron overload — extra iron absorption is harmful

Bottom line: Take vitamin C with iron-rich meals and iron supplements — it works, but the clinical hemoglobin gain over iron alone is modest.

SourceHooper et al., 2017 — Proceedings of the Nutrition Society Li et al., 2023 — Blood (ASH)

Common cold duration (regular daily use)

Supplement benefit

Good Evidence

The 2013 Cochrane review (29 trials, 11,306 participants) found regular ≥200 mg/day vitamin C does NOT reduce cold incidence in the general population (RR 0.97). It does shorten cold duration by 8% in adults and 14% in children when taken every day. Therapeutic vitamin C started after symptoms begin showed no consistent benefit. A striking subgroup — marathon runners, skiers, soldiers on subarctic training — saw cold incidence halved (RR 0.48), suggesting benefit is concentrated in extreme physical/cold stress.

Effect size

8% shorter colds in adults / 14% in children with daily ≥200 mg; no incidence reduction in non-athletes

Time to effect

Weeks (must be taken regularly before infection)

Best fit

People who can commit to daily intake well before cold season; endurance athletes; soldiers in cold conditions

Less likely

Adults wanting to abort an active cold by starting vitamin C after symptom onset

Bottom line: Worth it for endurance athletes and people who'll take it daily through cold season. Don't start it after you're already sick — that doesn't help.

SourceHemilä & Chalker, 2013 — Cochrane Database of Systematic Reviews

Cardiovascular disease prevention

Supplement benefit

Limited Evidence

Observational studies link higher vitamin C intake from food (not supplements) with lower CV mortality, but large RCTs of vitamin C supplementation have not shown reduced cardiovascular events. The Physicians' Health Study II (500 mg/day for ~10 years) found no overall effect on major CV events. Dietary produce intake — which carries vitamin C plus fiber, potassium, and many other nutrients — is the actionable target, not the isolated vitamin.

Effect size

No consistent reduction in CV events from supplementation in long-term RCTs

Time to effect

Not established for supplementation

Best fit

People who can replace supplements with daily fruit/vegetable intake

Less likely

Adults already meeting RDA and seeking a CV-mortality benefit from extra supplementation

Bottom line: Eat the produce. Isolated vitamin C supplements have not been shown to prevent heart disease.

SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

Cancer prevention

Mechanism only

Mixed Evidence

Vitamin C is a potent antioxidant in vitro, and dietary intake correlates with lower risk of some cancers in observational studies. However, randomized trials of oral vitamin C supplementation have not shown reduced cancer incidence or mortality. High-dose intravenous vitamin C is a separate, active research area in oncology — it should not be confused with oral supplements, which cannot reach the pharmacologic plasma levels achieved by IV.

Effect size

No consistent oral-supplement effect; IV vitamin C is investigational and separate

Time to effect

Not established

Best fit

Research participants in IV vitamin C oncology trials under medical supervision

Less likely

Healthy adults using oral megadoses for cancer prevention

Bottom line: Don't take oral high-dose vitamin C to prevent or treat cancer — it doesn't work that way and may interact with chemotherapy.

SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

How it works

Ascorbic acid acts as a cofactor for enzymes that build collagen, the protein that gives structure to skin, blood vessels, tendons, and bones. It also recycles other antioxidants like vitamin E, supports neurotransmitter synthesis, and substantially increases absorption of non-heme iron from plant foods. It is absorbed in the small intestine through both passive diffusion and active transport. At low to moderate doses absorption is highly efficient, but at very high oral doses (above 1,000 mg) the fraction absorbed drops sharply and excess is excreted in urine.

How to take it

1. Typical dose

• 75–90 mg/day to meet the RDA (women / men) • 200–500 mg/day for cold-season prophylaxis (only modest benefit; daily commitment required) • 25–100 mg taken with non-heme iron sources to boost iron absorption • Smokers add 35 mg/day to whatever target

2. Higher studied dose

Up to 1,000–2,000 mg/day for short-term use; doses above 2,000 mg/day commonly cause diarrhea and offer no proven additional benefit for healthy adults.

3. Timing

Take with food or water. With iron supplements, take vitamin C at the same time as iron to enhance absorption.

4. With food

With or without food; with food if it causes stomach upset.

5. Split dosing

Single daily dose at 75–500 mg is fine. Split doses above 500 mg/day across the day — absorption saturates at ~200 mg per dose and high single doses are excreted in urine.

6. How long to try

Indefinite at RDA-level doses. For cold-duration benefit, take daily through cold season (Nov–Mar in temperate climates).

What to track

Cold duration (days from first symptom to resolution) if using for that purpose

GI symptoms — diarrhea or cramps signal you're above your tolerance threshold

Iron status (ferritin, hemoglobin) if pairing with iron for IDA treatment

Kidney stone history — discuss high doses with your clinician if you've had stones

Bottom line: Most people don't need a supplement — a single orange or red pepper covers a day's RDA. If you supplement, 75–500 mg/day is the practical safe range; doses above 2,000 mg/day cause diarrhea without added benefit.

6 commercial forms

Compare the main delivery options and what they’re best suited for.

Ascorbic acid

Standard

The original supplemental form and the same molecule found in food. Cheap, well absorbed, and the form used in most clinical trials. Mildly acidic, which can cause stomach upset at high single doses.

Reference form; fully bioavailable up to ~200 mg per dose.

Sodium ascorbate

Buffered

Non-acidic sodium salt — gentler on the stomach than ascorbic acid. Each 1,000 mg contributes ~111 mg of sodium; not ideal if you're on a sodium-restricted diet.

Equivalent to ascorbic acid; better tolerated at high doses.

Calcium ascorbate (Ester-C)

Buffered + calcium

Buffered with calcium for stomach tolerance. Marketing claims of dramatically higher bioavailability are not consistently supported by independent research.

Comparable to ascorbic acid; tolerability advantage only.

Liposomal vitamin C

Premium claim

Vitamin C encapsulated in phospholipid vesicles. Some absorption studies show higher peak plasma levels than equivalent oral doses, but the clinical advantage over plain ascorbic acid is unclear for most uses.

Possibly higher than oral; rarely worth the price markup.

Intravenous vitamin C

Medical use only

Bypasses gut absorption to reach much higher plasma concentrations than oral dosing can achieve. Investigational in some oncology research. Not interchangeable with oral supplements and not used for general supplementation.

Reaches pharmacologic plasma levels; oral cannot match.

Food (whole produce)

Best source

A single medium orange, half a red bell pepper, or a kiwi covers the daily RDA. Whole food sources come with fiber, potassium, and other phytonutrients; observational evidence ties produce intake — not supplements — to lower mortality.

Naturally well absorbed; preferred source.

Safety

Know the common side effects, key cautions, and who should avoid it.

Common side effects

diarrhea (at >2,000 mg/day)bloatingstomach crampsnauseaheadache

Serious risks

Doses above the UL of 2,000 mg/day commonly cause GI symptoms (diarrhea, cramps); the threshold varies person-to-person.
SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet
Chronic high doses (≥1,000 mg/day) may modestly increase oxalate kidney stone risk in people prone to them, since vitamin C is partially metabolized to oxalate.
SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet
Increases non-heme iron absorption — a problem in hemochromatosis or other iron-overload conditions where extra iron causes organ damage.
SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet
May cause hemolysis in people with G6PD deficiency when given in very high IV doses; oral supplementation at typical doses appears safe.
SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

Who should avoid it

People with hemochromatosis, thalassemia, or other iron-overload disorders — vitamin C drives more iron absorption.
SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet
People with a history of oxalate kidney stones considering chronic doses >1,000 mg/day — discuss with a clinician.
SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet
Anyone undergoing chemotherapy or radiation without first clearing high-dose vitamin C with their oncologist.
SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

Pregnancy & breastfeeding

Pregnancy RDA is 80–85 mg/day (lactation 115–120 mg/day). Doses within RDA are safe. Doses above the 2,000 mg/day UL haven't been studied for teratogenic risk and are not recommended.

SourceMotherToBaby Vitamin C Fact Sheet — OTIS / NCBI Bookshelf

Bottom line: Very safe up to about 1,000 mg/day for almost everyone. Hemochromatosis, oxalate stone history, and active chemotherapy are the main reasons to be cautious with higher doses.

Interactions

chemotherapy and radiation therapyModerate

Vitamin C in supplements (especially high doses) may interact with oxidative cancer therapies. Talk to your oncologist before taking vitamin C above the RDA during active treatment.

SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

statins (especially with niacin)Minor

Vitamin C combined with other antioxidants may attenuate the HDL-raising effect of simvastatin/niacin combination therapy. Effect is modest and only relevant to that specific combination.

SourceNIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

non-heme iron (food or supplements)Minor

This is a beneficial interaction in iron-deficient people: vitamin C significantly boosts non-heme iron absorption. It's a problem in iron overload (hemochromatosis).

SourceHooper et al., 2017 — Proceedings of the Nutrition Society NIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet

aluminum-containing antacidsMinor

Vitamin C may increase aluminum absorption from antacids. Probably not clinically meaningful for most people, but separate doses if you have chronic kidney disease.

Protocols featuring Vitamin C (ascorbic acid)

Evidence-backed routines where Vitamin C (ascorbic acid) plays a role.

Birth Control Companion

medication

Combined oral contraceptives (estrogen + progestin) are one of the most-prescribed medications globally, with hundreds of millions of users. Long-term use is documented to deplete several nutrients: B6, B12, folate, magnesium, zinc, CoQ10, and vitamin C — with the depletion mechanism varying by nutrient (some via altered absorption, others via increased turnover). The clinical relevance: depleted B vitamins are implicated in oral contraceptive-related mood changes, fatigue, headaches, and elevated homocysteine. Magnesium depletion may contribute to migraines and PMS-like symptoms common in pill users. This protocol is for women ACTIVELY on combined oral contraceptives, progestin-only pills, or other hormonal contraceptives (patch, ring, implant, IUD with hormone, injection). It''s NOT for non-hormonal IUDs (copper) or barrier methods. CRITICAL: this protocol does NOT advise stopping contraception. It supports nutritional status while you''re on hormonal birth control. If you''re experiencing mood changes, fatigue, headaches, or other side effects you suspect are pill-related, this stack may help — but also consider discussing alternative formulations or methods with your prescriber. Different pills affect different women differently.

Daily Immune Foundation

immunity

Year-round immune support is mostly about correcting common nutrient gaps rather than "boosting" immunity (a misleading framing — you can''t make a healthy immune system more reactive without causing autoimmune problems). The four supplements with the strongest evidence for general immune support are vitamin D3 (the single most-evidenced supplement for respiratory infection prevention in deficient adults), zinc, vitamin C (modest cold-prevention effect), and quercetin (mast cell modulation + general antiviral activity in vitro). This stack is for daily use during cold/flu season, in immunocompromising situations (heavy training, chronic stress, frequent travel), or as preventive maintenance. For acute cold/flu treatment, see Cold/Flu Recovery (Acute). The most-leveraged immune intervention is sleep, not supplementation. A single night of poor sleep reduces natural killer cell activity by ~70%.

Skin & Collagen Support

beauty

Skin appearance is driven by hydration, collagen turnover, oxidative stress, and UV damage — most of which are downstream of lifestyle. Supplements can support but not replace topical sunscreen, sleep, hydration, and a diverse diet. The strongest evidence is for hydrolyzed collagen peptides (multiple trials show improvements in skin hydration and elasticity after 8-12 weeks) and vitamin C (cofactor in collagen synthesis). Hyaluronic acid taken orally has emerging evidence for skin hydration. The "anti-aging" supplement category is rife with overpromising — the gains are real but modest, and 90% of skin appearance comes from sun protection and not smoking.

Cold/Flu Recovery (Acute)

immunity

Acute upper respiratory infection treatment is fundamentally different from daily immune support — different dosing, different ingredients, and a short-cycle (7-10 day) approach rather than chronic supplementation. The supplements with the best acute evidence are elderberry (Sambucus nigra) for influenza specifically, high-dose zinc lozenges (zinc acetate or gluconate) for cold duration reduction, vitamin C at higher doses started at symptom onset, and NAC for mucus thinning and antioxidant support. The Cochrane reviews on these are reasonably positive for elderberry and zinc; vitamin C is modest; NAC has clean evidence for respiratory symptom reduction. This is a 7-day protocol — START at first symptom (sore throat, fatigue, body aches before the cold/flu is fully established) and continue through resolution. If you have severe symptoms (high fever, difficulty breathing, dehydration, chest pain), are at high risk (over 65, immunocompromised, pregnant, multiple comorbidities), or symptoms worsen instead of improving after 5-7 days — see your doctor. Bacterial pneumonia, flu requiring antivirals, and COVID requiring monitoring all need medical attention beyond supplementation.

Adrenal / Burnout Recovery

hormones

"Adrenal fatigue" is not a recognized medical condition — the adrenals don''t actually get tired. What IS real is occupational burnout (recognized by the WHO) and HPA-axis dysregulation: chronic stress flattens the normal diurnal cortisol curve, producing morning fatigue, "tired but wired" evenings, and emotional exhaustion. This pattern is distinct from depression or anxiety, though it overlaps with both. The supplement stack here targets HPA-axis modulation (ashwagandha, rhodiola), cortisol-utilization cofactors (vitamin C, B-complex), and acute cortisol blunting (phosphatidylserine). It does NOT replace addressing the upstream cause — chronic occupational, financial, or relationship stress — which is the only durable fix. Supplements support recovery; they don''t enable continued burnout. If you''re experiencing significant emotional exhaustion, cynicism, reduced sense of accomplishment, sleep disruption, and physical symptoms — those are clinical burnout signs, and addressing them often requires more than supplements (workload reduction, therapy, sometimes time away from work).

Kids Immune Support

kids

Frequent cold and flu illness in children is developmentally normal — young children get 6-10 viral upper respiratory infections per year as their immune system encounters new pathogens for the first time. This protocol is for: prevention during the school year (especially fall and winter), acute treatment when illness starts, and recovery support. The pediatric evidence base is smaller than for adults but the three core supplements — elderberry, zinc, and vitamin C — have reasonable trial evidence in children. CRITICAL: This is for OTHERWISE HEALTHY children with garden-variety cold and flu illness. Children with high fever, difficulty breathing, dehydration, prolonged symptoms, or chronic conditions need pediatric medical evaluation, not supplementation. Pediatric dosing matters. Adult doses are inappropriate for kids. Use age-appropriate pediatric formulations.

Seasonal Allergy Relief

immunity

Seasonal allergies (hay fever, allergic rhinitis, allergic conjunctivitis) affect 20-30% of adults — and the supplement category for them is dramatically under-developed relative to the demand. The mechanism behind allergy symptoms is mast cell histamine release in response to pollens, mold, or other seasonal allergens. The supplements with the strongest mast-cell-stabilizing and antihistamine evidence are quercetin (the most-studied natural antihistamine), vitamin C (modest antihistamine activity at higher doses), and stinging nettle (small trials specifically for allergic rhinitis). Butterbur has rigorous trial evidence comparable to cetirizine but requires PA-free formulations and short-course use. This stack is for mild-to-moderate seasonal symptoms and as a complement to standard antihistamines. Severe asthma or anaphylaxis-prone individuals need a proper allergist evaluation, not a supplement protocol.

Travel Immunity Kit

travel

Air travel is an immune-compromise event: dry cabin air dries out mucous membranes, recirculated air increases viral exposure, sleep disruption suppresses immune function, and physical stress raises cortisol. The goal isn't "boost" immunity (a misleading framing) — it's correct any nutrient gaps that would otherwise dim the immune response, and reduce the severity and duration of any infection you do pick up. Vitamin D and zinc are the highest-leverage nutrients here. Vitamin C and quercetin have smaller, supportive roles. This is a 10-day protocol: start 3 days before travel and continue for 7 days after.

Food sources

Food	Amount	%DV
Red pepper, sweet, raw	½ cup (95 mg)	106%
Orange juice	¾ cup (93 mg)	103%
Orange, medium	1 fruit (70 mg)	78%
Grapefruit juice	¾ cup (70 mg)	78%
Kiwifruit, medium	1 fruit (64 mg)	71%
Green pepper, sweet, raw	½ cup (60 mg)	67%
Broccoli, cooked	½ cup (51 mg)	57%
Strawberries, fresh sliced	½ cup (49 mg)	54%
Grapefruit, half medium	½ fruit (39 mg)	43%
Tomato juice	¾ cup (33 mg)	37%
Cantaloupe	½ cup (29 mg)	32%
Cabbage, cooked	½ cup (28 mg)	31%
Potato, baked	1 medium (17 mg)	19%
Tomato, raw	1 medium (17 mg)	19%

Red pepper, sweet, raw

Amount: ½ cup (95 mg)
%DV: 106%

Orange juice

Amount: ¾ cup (93 mg)
%DV: 103%

Orange, medium

Amount: 1 fruit (70 mg)
%DV: 78%

Grapefruit juice

Amount: ¾ cup (70 mg)
%DV: 78%

Kiwifruit, medium

Amount: 1 fruit (64 mg)
%DV: 71%

Green pepper, sweet, raw

Amount: ½ cup (60 mg)
%DV: 67%

Broccoli, cooked

Amount: ½ cup (51 mg)
%DV: 57%

Strawberries, fresh sliced

Amount: ½ cup (49 mg)
%DV: 54%

Grapefruit, half medium

Amount: ½ fruit (39 mg)
%DV: 43%

Tomato juice

Amount: ¾ cup (33 mg)
%DV: 37%

Cantaloupe

Amount: ½ cup (29 mg)
%DV: 32%

Cabbage, cooked

Amount: ½ cup (28 mg)
%DV: 31%

Potato, baked

Amount: 1 medium (17 mg)
%DV: 19%

Tomato, raw

Amount: 1 medium (17 mg)
%DV: 19%

Choosing a product

What to look for on the label — and what to be skeptical of.

Look for…

Look for 'ascorbic acid' or 'sodium ascorbate' — both are well absorbed and inexpensive

Third-party tested (USP, NSF, ConsumerLab) — confirms label dose

75–500 mg per capsule is the practical daily-use range

Time-release / extended-release formulations may modestly improve absorption above ~200 mg

Buffered ascorbate (sodium, calcium, or magnesium ascorbate) is gentler if plain ascorbic acid causes stomach upset

Be skeptical of…

'Mega-dose immune booster' at 5,000–10,000 mg per serving — excess is excreted in urine and causes diarrhea

'Liposomal' delivery claims of dramatically higher absorption — evidence is limited and not strong enough to justify the price markup for most uses

'Cures the common cold' — daily use shortens duration modestly; nothing aborts a cold once symptoms start

'Cancer-fighting' or 'anti-aging' claims on oral vitamin C — not supported by RCTs

'Bioflavonoid' or 'rose hip' blends marketed as superior — bioflavonoids don't measurably improve vitamin C absorption in healthy adults

Frequently asked questions

Is ascorbic acid the same as vitamin C?⌄

Yes. Ascorbic acid is the chemical name for vitamin C and is the form your body uses. Other forms in supplements (sodium ascorbate, Ester-C) are also vitamin C, just buffered.

Does ascorbic acid hurt the stomach?⌄

Some people experience stomach upset at higher doses because of its acidity. Taking it with food or using buffered forms helps.

How much ascorbic acid can I take per day?⌄

The upper limit is 2,000 mg per day for adults. Beyond that you risk gastrointestinal side effects with no added benefit.

Does ascorbic acid help iron absorption?⌄

Yes, substantially. Taken at the same time as iron from plants or supplements, ascorbic acid can multiply absorption.

Can I get enough ascorbic acid from food?⌄

Yes. One serving of citrus fruit, bell pepper, broccoli, or strawberries provides the daily requirement for most adults.

References by claim

Scurvy prevention and treatment

NIH Office of Dietary Supplements — Vitamin C — Health Professional Fact Sheet (2021) link

Common cold duration (regular daily use)

Hemilä & Chalker, 2013 — Cochrane Database of Systematic Reviews (2013) link

Non-heme iron absorption

Hooper et al., 2017 — Proceedings of the Nutrition Society (2017) link

Li et al., 2023 — Blood (ASH) (2023) link

Safety

MotherToBaby Vitamin C Fact Sheet — OTIS / NCBI Bookshelf (2024) link

Other references

Vitamin C (ascorbic acid) on Wikidata — Wikidata link

L-ascorbic acid (ChEBI:29073) — ChEBI link

Vitamin C on NIH DSLD — NIH Dietary Supplement Label Database link

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Evidence-based·Last reviewed May 31, 2026·Evidence current as of May 31, 2026·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.