# Vitamin C: Immune Support and Antioxidant Power

Essential Vitamins | By Longevity Futures Research Team | Updated November 2025

Vitamin C, also known as ascorbic acid, is perhaps the most well-known vitamin worldwide. This essential water-soluble nutrient is critical for immune function, collagen synthesis, antioxidant protection, and numerous other physiological processes that impact longevity and healthy aging.

Unlike most animals, humans cannot synthesize vitamin C and must obtain it from diet or supplements. This genetic quirk—shared with guinea pigs and some primates—means that maintaining adequate intake is essential for survival and optimal health.

Beyond Scurvy: While vitamin C is famous for preventing scurvy, optimal levels do far more than prevent deficiency disease. Higher intakes support robust immune function, protect against oxidative stress, enhance collagen production for skin and joints, and may reduce the risk of chronic diseases associated with aging.
90 mg
RDA for Men
75 mg
RDA for Women
2,000 mg
Upper Limit
200 mg
Optimal Daily Intake

## Immune System Support

Vitamin C is concentrated in immune cells at levels 10-100 times higher than blood plasma, highlighting its importance for immune function:

- Neutrophil function: Enhances the ability of these first-responder immune cells to engulf and destroy pathogens
- Lymphocyte proliferation: Supports the rapid multiplication of T and B cells during infection
- Antibody production: Required for optimal immunoglobulin synthesis
- Interferon production: Supports antiviral signaling molecules
- Barrier function: Maintains skin and epithelial integrity against pathogen entry

Cold and Flu Evidence: Meta-analyses show that regular vitamin C supplementation reduces cold duration by 8% in adults and 14% in children. While it doesn't prevent colds in the general population, it reduces cold incidence by 50% in people under physical stress (marathon runners, soldiers, skiers). Higher doses (1-2g daily) at cold onset may further reduce duration.

## Antioxidant Protection

Vitamin C is one of the body's primary water-soluble antioxidants, protecting against oxidative damage that contributes to aging and disease:

- Free radical neutralization: Directly scavenges reactive oxygen species
- Vitamin E regeneration: Recycles oxidized vitamin E back to its active form
- Glutathione support: Helps maintain levels of this master antioxidant
- DNA protection: Reduces oxidative damage to genetic material
- LDL oxidation prevention: May protect against atherosclerosis

The Antioxidant Network: Vitamin C doesn't work alone—it's part of an interconnected antioxidant network. It regenerates vitamin E, supports glutathione, and works synergistically with other antioxidants. This is why whole-food sources and comprehensive supplementation often outperform isolated high-dose vitamin C.

## Collagen Synthesis

Vitamin C is absolutely essential for collagen production—without it, collagen synthesis stops completely. This affects:

- Skin health: Collagen provides structure, firmness, and elasticity to skin
- Wound healing: Collagen is essential for tissue repair
- Joint health: Cartilage contains significant collagen
- Blood vessel integrity: Collagen strengthens arterial walls
- Bone health: Collagen provides the organic matrix for bone
- Gum health: Collagen maintains gum tissue structure

Skin Aging Research: Studies show that higher vitamin C intake is associated with less skin wrinkling and better skin appearance. Topical and oral vitamin C both contribute to skin health by supporting collagen synthesis and providing antioxidant protection against UV damage.

## Iron Absorption

Vitamin C dramatically enhances non-heme iron absorption (the type found in plants and supplements):

- Reduces iron to absorbable form: Converts Fe3+ to Fe2+
- Overcomes absorption inhibitors: Counters phytates and tannins in plant foods
- Important for vegetarians: Can increase iron absorption 2-6 fold

Taking vitamin C with iron-rich meals or supplements significantly improves iron status, especially important for women, vegetarians, and those with iron deficiency.

## Best Food Sources of Vitamin C

#### Red Bell Peppers

190 mg per cup raw. Exceptionally rich—more than oranges.

#### Oranges

70 mg per medium orange. Classic source with additional bioflavonoids.

#### Kiwi

71 mg per fruit. Excellent source with fiber and vitamin K.

#### Broccoli

81 mg per cup cooked. Retains vitamin C well with light cooking.

#### Strawberries

89 mg per cup. Delicious source with antioxidant polyphenols.

#### Brussels Sprouts

97 mg per cup cooked. High vitamin C with fiber and other nutrients.

## Forms of Vitamin C Supplements

### Ascorbic Acid

The standard form, well-absorbed and effective. May cause GI upset in large doses due to acidity. Most affordable option.

### Buffered Vitamin C

Ascorbic acid combined with minerals (calcium, magnesium, sodium). Gentler on the stomach; good for those with sensitivity.

### Liposomal Vitamin C

Encapsulated in lipid spheres for enhanced absorption. May achieve higher blood levels than regular ascorbic acid. More expensive but potentially more effective.

### Ester-C

Calcium ascorbate with vitamin C metabolites. Non-acidic and well-tolerated. Contains dehydroascorbate which may have additional benefits.

## Optimal Dosing

While the RDA (75-90mg) prevents scurvy, optimal health may require higher intakes:

- Basic health maintenance: 200-500mg daily
- Enhanced immune support: 500-1000mg daily
- During illness: 1000-2000mg in divided doses
- High stress or heavy exercise: 500-1000mg daily
- Smokers: Add 35mg minimum; 500mg+ recommended

Divided Doses: Vitamin C absorption decreases with increasing doses. Taking 250-500mg multiple times daily achieves higher sustained blood levels than a single large dose. Excess vitamin C is excreted in urine within hours, so spread intake throughout the day.

## Vitamin C and Longevity

Higher vitamin C intake and blood levels are associated with multiple longevity-related benefits:

- Reduced mortality: Studies link higher vitamin C with lower all-cause mortality
- Cardiovascular protection: Supports endothelial function and may reduce blood pressure
- Cancer prevention: Higher intake associated with reduced risk of certain cancers
- Cognitive preservation: May protect against age-related cognitive decline
- Skin aging: Supports collagen and protects against photoaging
- Telomere length: Some studies suggest vitamin C may help preserve telomere length

## Recommended Vitamin C Supplement

### Thorne Vitamin C 500mg with Bioflavonoids

Vitamin C enhanced with citrus bioflavonoids from oranges for improved absorption and synergistic antioxidant benefits. Supports immune function, cellular energy production, and collagen synthesis. Third-party certified, gluten-free. 90 servings.

$21.00
View on Amazon

## Related Articles

- Vitamin E: Cellular Protection and Skin Health
- Vitamin D: Bone Health and Immune Function
- Best Collagen Supplements for Anti-Aging
- Antioxidants for Skin: Vitamin C, E, and Astaxanthin