Deficiency/Immunity/Heart

Vitamin C

Water-soluble vitamin that prevents deficiency, modestly shortens colds, and best helps adults with low produce intake.

Vitamin C

Water-soluble vitamin that prevents deficiency, modestly shortens colds, and best helps adults with low produce intake.

score

evidence

Safe

risk

Proven Benefits

01Corrects deficiency/scurvy

02Shortens common cold duration

03Lowers blood pressure modestly

04May improve vascular function

Chemical Forms

Recommended

Ascorbic acid
Sodium ascorbate
Calcium ascorbate

Avoid

Liposomal vitamin C sold at large price premiums (no clear outcome advantage for routine use)
Time-release megadose products (more expensive, no clear clinical advantage)

Expert Note

Plain ascorbic acid is the reference form used in most trials and is well absorbed at usual doses. Buffered mineral ascorbates can be easier on the stomach for sensitive users. Percentage absorption is highest at smaller doses and falls as doses rise, so premium delivery systems have not shown clearly superior everyday outcomes.

Protocol

Amount

200-500 mg

Frequency

Once daily

When

Any time of day — consistency matters more than timing; take with food if you get stomach upset.

Condition-Based Dosing

Low fruit and vegetable intake

200-500 mg daily— Usually enough to cover the gap when diet quality is inconsistent.

Smokers or frequent secondhand smoke exposure

250-500 mg daily— Smoking increases oxidative turnover and tends to lower blood vitamin C levels.

At first signs of a cold

500 mg 1-2 times daily for up to 5-7 days— Evidence is stronger for regular daily use than for starting only after symptoms begin.

Safety & Limits

Upper Safe Limit

2000 mg/day (IOM UL for adults)

Cycling

Safe for continuous use

Contraindications

Hemochromatosis or other iron-overload disorders — can increase non-heme iron absorption

History of calcium oxalate kidney stones or hyperoxaluria — high doses may raise urinary oxalate

Severe kidney disease — high doses may increase oxalate burden

Synergies

Iron

Vitamin C reduces ferric to ferrous iron and forms soluble complexes, improving absorption of non-heme iron from supplements and plant foods.

Collagen peptides

Vitamin C is required for hydroxylation of proline and lysine during collagen synthesis, so it provides a needed cofactor when taking collagen.

Vitamin E

Vitamin C can help regenerate oxidized vitamin E, supporting antioxidant activity in cell membranes.

Avoid Combining With

✕Smoking or secondhand smoke exposure (increases turnover and lowers plasma vitamin C)
✕Heavy alcohol use (associated with lower status and poorer dietary intake)
✕High-heat cooking or long storage of produce (destroys vitamin C in food)

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