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Water-soluble vitamin

Vitamin C

ascorbic acid

Collagen synthesis, antioxidant, iron absorption, wound healing, immune function

Essential nutrient

Reference intakes (RDA or AI) are set by the National Academies of Sciences, Engineering, and Medicine. Deficiency thresholds come from clinical and WHO guidance.

At a glance

Women, 19-50

75 mg (+35 mg if smoker)

Men, 19-50

90 mg (+35 mg if smoker)

Upper limit (adults)

2,000 mg/day

How common is deficiency?

Uncommon (scurvy is rare); low blood levels are more common in smokers and people with very limited diets

Food sources

Animal sources

Small amounts in raw liver and fish roe

Plant sources

Bell peppers, citrus fruits, kiwi, strawberries, guava, broccoli, Brussels sprouts, tomatoes, potatoes

Deficiency and testing

Signs of deficiency

Scurvy: fatigue, bleeding/swollen gums, easy bruising, corkscrew hairs, poor wound healing, joint pain, loose teeth

Who is at higher risk

Smokers, very restricted diets, alcohol/drug dependence, dialysis, older adults living alone, severe malabsorption

How it is tested

Plasma/serum ascorbic acid (HPLC); leukocyte (buffy coat) vitamin C - better long-term marker

Cut-offs

Plasma vitamin C <11 umol/L (<0.2 mg/dL) = deficiency; 11-23 umol/L = low

Symptoms are not specific. Only a clinician with the right tests can tell whether you are deficient.

Supplement forms

Common forms

ascorbic acid, buffered (sodium/calcium/magnesium ascorbate), Ester-C (calcium ascorbate + metabolites), liposomal vitamin C, with bioflavonoids, time-release, gummies, IV (clinical).

More effective

plain ascorbic acid or buffered ascorbate in divided doses of about 200-500 mg (well absorbed, cheap); buffered forms are gentler on the stomach. Oral absorption falls sharply above about 1 g in one dose.

Less effective

'megadose' single servings (most is excreted, may cause diarrhea); time-release and bioflavonoid blends (no clear advantage over plain ascorbic acid); liposomal vitamin C (higher blood levels in some small studies, but limited clinical evidence and higher cost); Ester-C (no consistent advantage in human trials).

Safety, interactions and halal notes

Safety and interactions

Upper limit for adults: 2,000 mg/day. Going above the upper limit over time can cause harm, so check labels and talk to a clinician before high-dose supplements.

Halal note

The nutrient itself is not a halal question. For supplements, check the delivery form: gelatin (pork or non-halal bovine), capsule shells, glycerin, and alcohol-based carriers need halal certification. Ask for the halal certificate, not just a label claim. This is general guidance, not a certification.

Frequently asked questions

How much Vitamin C do adults need per day?

Women 19-50: 75 mg (+35 mg if smoker). Men 19-50: 90 mg (+35 mg if smoker). Upper limit: 2,000 mg/day. Needs change with age, pregnancy and health conditions.

What are the signs of Vitamin C deficiency?

Scurvy: fatigue, bleeding/swollen gums, easy bruising, corkscrew hairs, poor wound healing, joint pain, loose teeth. These signs are not specific, so only a clinician with the right tests can confirm a deficiency.

What are the best food sources of Vitamin C?

Animal sources: Small amounts in raw liver and fish roe. Plant sources: Bell peppers, citrus fruits, kiwi, strawberries, guava, broccoli, Brussels sprouts, tomatoes, potatoes.

Which form of Vitamin C supplement is best?

Sources

NIH Office of Dietary Supplements fact sheet

← Back to the full nutrient guide

This page is for education only and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Supplements are not intended to diagnose, treat, cure or prevent any disease. Talk to a qualified clinician before starting a supplement, especially if you are pregnant, breastfeeding, take medicine or have a medical condition. Daily needs are US reference intakes for adults 19-50.

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