Vitamin C (Ascorbic Acid)Vitamin

• Stopping colds from happeningNot shown to help

  The single most common reason people buy vitamin C, and the Cochrane review says no.
  
  Routine daily use of at least 200 mg/day did not reduce how often people in the general population caught colds [4].
  
  That is placebo-controlled trial evidence pooled across decades, not an absence of data [4]. ^[4]

• Colds under extreme physical or cold stressLikely helps

  The one population where the cold finding flips. In marathon runners, skiers and soldiers, prophylactic vitamin C cut cold incidence by about 50% [4].
  
  NIH's Office of Dietary Supplements reports the same figure [1]. Whether it generalises past that kind of extreme exertion or cold exposure is not established. ^[4]

• Cold duration, if you were already taking itLikely helps

  Regular use modestly shortened colds — about 8% in adults and 14% in children [1].
  
  On a week-long cold, 8% is roughly half a day. Real, consistent, and much smaller than the marketing implies [4].
  
  Starting vitamin C only after symptoms begin had no effect on duration or severity [1]. ^[1]

• Immune function generallyPossibly helps

  Carr and colleagues' review in Nutrients describes vitamin C supporting several innate and adaptive immune cell functions — neutrophil chemotaxis, phagocytosis, lymphocyte activity [13].
  
  Deficiency clearly impairs immunity and raises infection susceptibility [13].
  
  What that does not establish is a benefit from supplementing someone whose vitamin C status is already adequate [13]. ^[13]

• Skin and collagenPossibly helps

  The biochemistry is solid. Vitamin C is an essential cofactor for prolyl and lysyl hydroxylase, the enzymes that assemble collagen [1].
  
  Topical and dietary vitamin C are both associated with collagen support [1].
  
  Direct causal evidence for anti-ageing claims from oral supplementation specifically is much weaker than that biochemical rationale [1]. ^[1]

• Cancer riskNot shown to help

  Case-control studies link higher dietary vitamin C to lower risk of several cancers [1].
  
  Most randomised controlled trials found supplementation, alone or with other nutrients, did not reduce cancer risk [1].
  
  NIH ODS names a real limitation of those trials: plasma vitamin C is tightly regulated, so dosing people already at saturation may not move anything [1]. ^[1]

• Cardiovascular diseasePossibly helps

  The cohort studies do not agree with each other, per NIH ODS [1].
  
  The Nurses' Health Study found lower coronary heart disease risk with combined dietary and supplemental intake. A pooled analysis of 9 studies found benefit only above 700 mg/day supplemental [1].
  
  A 2008 meta-analysis concluded only dietary vitamin C was inversely associated with risk, not supplemental [1].
  
  Most intervention trials found no reduction in cardiovascular events. One — vitamin C plus vitamin E in postmenopausal women with existing coronary disease — showed increased all-cause mortality [1]. ^[1]

• Scurvy is the end state. Symptoms can appear within about one month of intake below roughly 10 mg/day
• Fatigue and malaise, with gum inflammation, come first
• Petechiae — small red or purple spots — along with ecchymoses and purpura
• Joint pain
• Poor wound repair
• Hyperkeratosis — rough, scaly skin
• Corkscrew-shaped body hairs
• Bleeding, swollen gums and tooth loss
• Easy bruising and nosebleeds
• Dry, splitting hair
• Reduced ability to resist infection
• Anemia, through impaired non-heme iron absorption plus bleeding
• Without correction, scurvy can be fatal^[1]

• Ascorbic acidMost people. Researchers still name plain, low-cost ascorbic acid the preferred supplemental source .

  Elemental content

  Plain vitamin C, the most common and best-studied supplement form [1]

  Absorption

  Bioavailability is equivalent to the ascorbic acid naturally present in foods such as orange juice or broccoli [1].

  Best for

  Most people. Researchers still name plain, low-cost ascorbic acid the preferred supplemental source [1].

• Mineral ascorbates and Ester-CPeople who find plain ascorbic acid harsh on the stomach.

  Elemental content

  Sodium ascorbate, calcium ascorbate and other mineral salts. Ester-C adds dehydroascorbate plus calcium threonate, xylonate and lyxonate [1]

  Absorption

  Human comparisons found no consistent, meaningful bioavailability advantage over plain ascorbic acid [1].
  
  One study did find Ester-C produced higher vitamin C concentrations inside white blood cells at 24 hours, despite similar plasma levels [1].

  Best for

  People who find plain ascorbic acid harsh on the stomach. The extra cost buys no demonstrated absorption gain [1].

• Ascorbic acid with bioflavonoidsNo distinct advantage has been shown over plain ascorbic acid .

  Elemental content

  Ascorbic acid combined with plant bioflavonoids [1]

  Absorption

  Grouped with the other alternative forms in NIH ODS's review, with no consistent bioavailability advantage found [1].

  Best for

  No distinct advantage has been shown over plain ascorbic acid [1].

• Liposomal vitamin CNothing settled yet. A 2025 scoping review notes many trials used 1–10 g doses that sidestep vitamin C's normal dose-de…

  Elemental content

  Ascorbic acid encapsulated in lipid vesicles — a delivery format, not a different vitamin [8]

  Absorption

  Small randomised crossover trials found meaningfully higher blood levels at matched doses.
  
  +30% area-under-curve for liposomal powder at 1,000 mg, +77% for a liquid suspension at the same dose, +35% for sodium ascorbate at about 4.25 g [8].
  
  Across formulations the range runs roughly 1.3x to nearly 2.4x higher AUC, with longer-lasting elevation [8].

  Best for

  Nothing settled yet. A 2025 scoping review notes many trials used 1–10 g doses that sidestep vitamin C's normal dose-dependent absorption, and asks for longer steady-state studies [8].

• Gastrointestinal upset at high doses

  The most common problem with large doses is unabsorbed vitamin C reaching the gut [1].
  
  That presents as diarrhea, nausea and abdominal cramps [1]. ^[1]

• Chemotherapy and radiation

  Vitamin C's antioxidant activity could in theory shield tumour cells from the oxidative damage those therapies rely on [1].
  
  The data are inconsistent, and some research suggests the opposite — that it shields normal tissue instead [1].
  
  NIH ODS recommends anyone undergoing chemotherapy or radiation consult their oncologist first, especially at high doses [1]. ^[1]

• Kidney stones in men

  The sources genuinely conflict, and this page is not settling it.
  
  A Swedish cohort of about 23,000 men followed 11 years found supplement users had roughly double the kidney stone risk of non-users [6]. A Harvard-cited Curhan study found the same.
  
  The signal sat at around 1,000 mg/day or more, in men specifically. Dietary vitamin C and general multivitamin use showed no such effect, and a near-identical study in women found no association [6].
  
  NIH ODS calls the overall vitamin C and oxalate evidence conflicting, and limits the best causal case to people who already have hyperoxaluria [1].
  
  The proposed mechanism is that some ingested vitamin C converts to oxalate [5]. ^[6]

• Hereditary hemochromatosis

  The same iron effect runs the wrong way here. In people with hereditary hemochromatosis, chronic high-dose vitamin C could in theory worsen iron overload [1]. ^[1]

• Warfarin

  Case reports describe high-dose vitamin C reducing warfarin's anticoagulant effect [14].
  
  The doses involved were roughly 1,000 mg/day and up, reaching about 16,000 mg/day in one case [14].
  
  Anyone on warfarin should speak to a physician before starting high-dose vitamin C [14]. ^[14]

• Non-heme iron absorption

  Vitamin C substantially increases absorption of non-heme, plant-based iron by reducing ferric iron to the more absorbable ferrous form [1].
  
  This one is usually welcome — it is the reason pairing lentils with citrus is standard advice [1]. ^[1]

• Niacin plus simvastatin

  Vitamin C, alongside other antioxidants, may blunt the HDL-cholesterol-raising effect of combined niacin and simvastatin therapy [1].
  
  NIH advises monitoring lipid levels in people taking statins and antioxidant supplements together. Whether this extends to other statin regimens is unclear [1]. ^[1]

Fruit and vegetables carry almost all of it. Vitamin C is not naturally present in grains, though it is added to some fortified breakfast cereals [1].

Per serving, against the 90 mg Daily Value: raw red sweet pepper, ½ cup — 95 mg (106% DV). Orange juice, ¾ cup — 93 mg (103% DV) [1].

One medium orange — 70 mg (78% DV). Grapefruit juice, ¾ cup — 70 mg (78% DV) [1].

One medium kiwifruit — 64 mg (71% DV) [1].

Raw green sweet pepper, ½ cup — 60 mg (67% DV). Cooked broccoli, ½ cup — 51 mg (57% DV) [1].

Fresh sliced strawberries, ½ cup — 49 mg (54% DV). Cooked Brussels sprouts, ½ cup — 48 mg (53% DV) [1].

Lower down: cantaloupe, ½ cup — 29 mg (32% DV). One medium raw tomato — 17 mg (19% DV) [1].

Cooked spinach, ½ cup — 9 mg (10% DV) [1].

Five varied servings of fruit and vegetables a day can supply more than 200 mg — well past the RDA, without a supplement in sight [1].

Cleveland Clinic's guidance is to take water-soluble vitamins like C on an empty stomach with a glass of water, since water is needed to absorb them [10].

That is about pairing with water, not about a particular hour [10].

The dose-response is where timing actually bites. NIH pharmacokinetic data show 70–90% absorption at moderate intakes of 30–180 mg/day [1].

Above 1 g/day absorption falls below 50%, with the surplus excreted in urine [1]. That is the physiological argument some sources make for splitting large doses across the day.

NIH's own fact sheet does not recommend dose-splitting as general practice [1].

Topical serum is a different route with different advice. Healthline's dermatologist sources suggest applying morning and night on freshly washed skin, before moisturiser and sunscreen, with reapplication roughly every 8 hours [11].