Linus Pauling won two Nobel Prizes, and then spent his later career insisting that megadoses of vitamin C could cure everything from the common cold to cancer. He was brilliant, stubborn, and mostly wrong about the megadose part. But his obsession did one useful thing: it made vitamin C the most studied vitamin in history. And the actual evidence — stripped of hype and wishful thinking — is still genuinely impressive.
Vitamin C (ascorbic acid) is a water-soluble antioxidant that humans can't synthesize. Most mammals make their own. We lost that ability somewhere in our evolutionary past when the gene for L-gulonolactone oxidase mutated into a pseudogene. So we're stuck eating it. Every day. Forever.
What Vitamin C Actually Does
Collagen synthesis. This is vitamin C's most fundamental role. It's a required cofactor for prolyl and lysyl hydroxylase — the enzymes that stabilize collagen's triple-helix structure. Without vitamin C, collagen falls apart. Literally. That's what scurvy is: your connective tissue disintegrating because your body can't make functional collagen. Bleeding gums, loose teeth, poor wound healing, and eventually death.
Antioxidant defense. Vitamin C donates electrons to neutralize reactive oxygen species (free radicals) before they damage DNA, proteins, and cell membranes. It also regenerates vitamin E after vitamin E has neutralized a free radical — an elegant recycling system.
Immune function. Vitamin C accumulates in immune cells (neutrophils, lymphocytes, phagocytes) at concentrations 10-100 times higher than plasma levels. It supports both innate and adaptive immunity by enhancing neutrophil migration, phagocytosis, and microbial killing. A review in Nutrients (2017) documented that vitamin C deficiency significantly impairs immune function and increases susceptibility to infections.
Iron absorption. Vitamin C converts ferric iron (Fe3+) to ferrous iron (Fe2+) in the gut, dramatically improving non-heme iron absorption. Taking 200 mg of vitamin C with an iron-rich meal or supplement can increase absorption 2-3 fold.
Neurotransmitter synthesis. Vitamin C is a cofactor for dopamine beta-hydroxylase, the enzyme that converts dopamine to norepinephrine. It's also involved in serotonin synthesis.
The Cold Question: Settled (Mostly)
Let's address the elephant in the room. Does vitamin C prevent or treat colds?
A landmark Cochrane review (2013, updated) analyzed 29 trials with over 11,000 participants on regular vitamin C supplementation (200 mg/day or more) for cold prevention:
- Prevention in the general population: Vitamin C did not reduce the incidence of colds. You get just as many colds whether you take it daily or not.
- Duration: Regular supplementation reduced cold duration by 8% in adults and 14% in children. That's about half a day shorter.
- Severity: Modestly reduced.
- Extreme physical stress: In five trials involving marathon runners, skiers, and soldiers in subarctic conditions, regular vitamin C supplementation reduced cold incidence by 52%. If you're running ultramarathons in January, vitamin C earns its keep.
- Therapeutic use (starting after symptoms begin): No consistent benefit. Taking vitamin C after you're already sick doesn't meaningfully shorten your cold.
The takeaway: daily vitamin C offers modest protection against cold duration if you're already taking it regularly. But it's not a treatment once you're symptomatic, and it doesn't prevent colds in most people.
Skin: Where Vitamin C Gets Interesting
Vitamin C's role in collagen synthesis makes it directly relevant to skin health. The skin contains high concentrations of vitamin C, particularly in the epidermis, where it serves dual roles as an antioxidant (protecting against UV-induced oxidative damage) and a collagen cofactor.
Topical vitamin C (L-ascorbic acid, typically in serums at 10-20% concentration) has better evidence for skin benefits than oral supplementation:
- Reduces photoaging (UV-induced wrinkles and pigmentation)
- Brightens skin by inhibiting tyrosinase (the enzyme that produces melanin)
- Enhances collagen production in the dermis
- Works together with vitamin E and ferulic acid for enhanced antioxidant protection
A study in the Journal of Clinical and Aesthetic Dermatology (2013) demonstrated that a stabilized topical vitamin C formulation improved wrinkles, roughness, and skin tone over 12 weeks.
Oral vitamin C supports skin health from the inside, but the effects are less dramatic than topical application because blood vitamin C levels plateau at relatively low supplemental doses.
Dosing: The Plateau Effect
Vitamin C absorption is dose-dependent and saturates quickly:
- At 200 mg, absorption is nearly 100%
- At 500 mg, absorption drops to about 75%
- At 1,000 mg, absorption is roughly 50%
- Above 1,000 mg, absorption continues to decline and unabsorbed vitamin C can cause osmotic diarrhea
Plasma levels plateau at oral doses of about 200-400 mg/day. Taking 2,000 mg doesn't double your blood levels — it mostly just increases what you excrete.
The RDA is 90 mg/day for men and 75 mg/day for women. Smokers need an additional 35 mg/day due to increased oxidative stress. Most nutrition researchers suggest 200-500 mg/day as a reasonable supplemental target — enough to saturate plasma without wasting money on megadoses.
The Tolerable Upper Intake Level is 2,000 mg/day. Above this, the primary risks are GI distress (diarrhea, nausea, cramps) and, in susceptible individuals, increased oxalate production that may raise kidney stone risk.
Food Sources: Easier Than You Think
You don't need supplements if you eat fruits and vegetables regularly:
| Food | Serving | Vitamin C (mg) |
|---|---|---|
| Red bell pepper | 1/2 cup raw | 95 |
| Orange | 1 medium | 70 |
| Kiwi | 1 medium | 64 |
| Broccoli | 1/2 cup cooked | 51 |
| Strawberries | 1/2 cup | 49 |
| Brussels sprouts | 1/2 cup cooked | 48 |
| Grapefruit | 1/2 medium | 39 |
| Tomato | 1 medium | 17 |
A single red bell pepper gets you over the RDA. Two kiwis do it. This is not a hard nutrient to get from food — unless your diet is genuinely devoid of fruits and vegetables.
Liposomal and Buffered Forms: Worth the Premium?
Liposomal vitamin C encapsulates ascorbic acid in phospholipid spheres (liposomes), theoretically improving absorption by bypassing the saturable intestinal transporter. Some small studies suggest modestly higher plasma levels compared to standard vitamin C at equivalent doses. Whether this translates to meaningful clinical benefits is unproven. It costs considerably more.
Buffered vitamin C (calcium ascorbate, sodium ascorbate) is less acidic, making it gentler on sensitive stomachs. Equally effective for raising vitamin C levels. A good option if plain ascorbic acid causes GI discomfort.
Ester-C is a branded form containing calcium ascorbate plus small amounts of vitamin C metabolites (dehydroascorbate, threonate). Marketing claims of superior absorption are not convincingly supported by independent research.
When to Talk to a Pro
Consult a healthcare provider if:
- You have a history of kidney stones (high-dose vitamin C increases urinary oxalate)
- You have hemochromatosis or other iron-loading conditions (vitamin C enhances iron absorption, which can worsen iron overload)
- You have G6PD deficiency (high-dose IV vitamin C can cause hemolytic anemia — relevant for IV protocols, not standard oral doses)
- You're undergoing cancer treatment (vitamin C can interfere with certain chemotherapy drugs)
- You have symptoms of scurvy (rare but occurs in people with extremely limited diets — elderly, people experiencing food insecurity, individuals with eating disorders)
FAQ
Does cooking destroy vitamin C? Partially. Vitamin C is heat-sensitive and water-soluble. Boiling vegetables can reduce vitamin C content by 50% or more. Steaming, microwaving, or stir-frying retains more. Raw is best for maximizing vitamin C, but cooked vegetables still contribute meaningful amounts.
Can vitamin C cause kidney stones? At high doses (above 1,000 mg/day), vitamin C is partially metabolized to oxalate, which can increase urinary oxalate and theoretically raise kidney stone risk. A Swedish cohort study found a modestly elevated risk in men taking vitamin C supplements above 1,000 mg/day. If you're stone-prone, keep supplemental doses moderate.
Is IV vitamin C better than oral? IV vitamin C can achieve plasma concentrations 30-70 times higher than oral doses — bypassing the intestinal absorption limit. This is used in some integrative cancer protocols and critical care research. For general health, it's unnecessary. Oral vitamin C at 200-500 mg/day saturates normal physiological needs.
A note from Living & Health: We're a lifestyle and wellness magazine, not a doctor's office. The information here is for general education and entertainment — not medical advice. Always talk to a qualified healthcare professional before making changes to your health routine, especially if you have existing conditions or take medications.
