Vitamin
Vitamin C
Also known as: Ascorbic acid, L-ascorbic acid, Ascorbate, Sodium ascorbate
Vitamin C is an essential water-soluble antioxidant required for collagen synthesis, immune function, and iron absorption. Calcium ascorbate is a buffered form that reduces gastric irritation.
Last reviewed June 2026 · Evidence graded from peer-reviewed research, not editorial opinion. Educational only — not medical advice.
Every Vitamin C product we have scored
| # | Product | Score | Per serving |
|---|---|---|---|
| 1 | Nutricost Collagen Powder for Women | 93 A | $1.27 |
| 2 | BulkSupplements Acerola Cherry Extract Powder | 90 A | $0.05 |
| 3 | Thorne Thyroid Health Complex | 90 A | $0.33 |
| 4 | Thorne Vitamin C 1,000 mg | 90 A | $0.32 |
| 5 | Pure Encapsulations EyeProtect Basics without zinc | 90 A | $1.00 |
| 6 | Nature Made B-Complex with C Caplets | 90 A | $0.11 |
| 7 | Garden of Life Vitamin Code Raw Vitamin C | 90 A | $0.46 |
| 8 | Thorne Broccoli Seed Extract | 89 A | $1.12 |
| 9 | Pure Encapsulations EyeProtect Basics | 89 A | $1.05 |
| 10 | Nutricost Calcium Ascorbate Powder | 89 A | $0.07 |
| 11 | MegaFood Skin, Nails & Hair 2 | 89 A | $0.87 |
| 12 | Thorne Advanced Nutrients | 88 A | $2.40 |
Scored on dose accuracy, form, label transparency and third-party testing. Per-serving cost is list price divided by servings per container. No brand pays to be listed or ranked.
Common questions
How much Vitamin C should I take?
The typical range is 500-2000mg daily. Safe long-term
When should I take Vitamin C?
Divided doses. Optional.
Which form of Vitamin C is best?
Ascorbic acid powder — Economical, acidic. Other forms in the catalog: Sodium ascorbate, Liposomal, Liquid gel, Capsules, Ascorbic acid, Buffered/Ester-C, Buffered C, Liposomal C, Buffered, Liposomal vitamin C, Ester-C, Powder, Buffered (sodium ascorbate), Calcium ascorbate.
Is Vitamin C safe?
Commonly reported: GI upset at high doses, Diarrhea. Serious warnings: Kidney stones risk at very high doses. Caution with kidney stones history
Which Vitamin C supplement scores highest?
Nutricost Collagen Powder for Women, at 93/100. Scored on dose accuracy, form, label transparency and third-party testing — no brand pays to be listed or ranked.
Daily target & upper limit
90 mg / day · UL 2000 mgVitamin C has an established daily reference intake. See best forms, label synonyms, upper-limit warnings, and top-scoring supplements:
Vitamin C dosage reference →Primary uses
- Immune support
- Antioxidant
- Collagen synthesis
- Iron absorption
- Enhanced immune support
- High-dose C therapy
- Cortisol reduction
- Exercise recovery
- Adrenal support
- Cortisol production
- Stress resilience
What systematic reviews concluded
Outcomes that systematic reviews of Vitamin C reached a verdict on: 4 with a benefit, 5 with no effect, 1 with harm reported, 5 unclear. Each is quoted from a review and linked to it on PubMed. How these were read.
Reviews found a benefit (4)
“Most clinical studies support a beneficial role of vitamin C supplementation in functional iron deficiency and in alleviating symptoms of RLS within this population.” PMID 41829943
“The findings suggest that vitamin C supplementation may reduce SBP by approximately 3.7 mmHg.” PMID 41784995
“Regular supplementation trials have shown that vitamin C reduces the duration of colds, but this was not replicated in the few therapeutic trials that have been carried out.” PMID 23440782
“Patients reported significant improvements in symptoms, including a 43% reduction in daily pelvic pain and a 37% reduction in dysmenorrhea.” PMID 41683896 · 2 reviews
Reviews found no effect (5)
“evidence does not support routine use of high-dose IVC in sepsis” PMID 41815850
“vitamin C supplementation does not appear to consistently modify post-exercise inflammatory or oxidative stress biomarkers.” PMID 41687812
“The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified” PMID 23440782
“Based on a very limited number of small randomized trials, vitamin C supplementation does not appear to consistently modify post-exercise inflammatory or oxidative stress biomarkers.” PMID 41687812
“The failure of vitamin C supplementation to reduce the incidence of colds in the general population indicates that routine vitamin C supplementation is not justified, yet vitamin C may be useful for people exposed to brief periods of severe physical exercise.” PMID 23440782
Harm reported (1)
“Some of the major risks include oxalate nephropathy and hemolysis in patients with glucose-6-phosphate dehydrogenase deficiency, especially with very large or repeated doses, suggesting pre-screening to avoid these risks.” PMID 41815850
Not enough to say: secondary hyperparathyroidism; diastolic blood pressure; inflammatory markers; cognitive performance/dementia risk; chronic wound healing.
6 findings from reviews in specific patient groups (such as cancer, pregnancy or surgery) are not shown here.
How it works
- Collagen hydroxylation cofactor
- Electron donor antioxidant
- Immune cell support
- Enhances iron absorption
Dosage
- Typical range
- 500-2000mg daily
- Timing
- Divided doses
- With food
- Optional
- Duration
- Safe long-term
- Special populations
- Higher needs when sick
Forms
- Ascorbic acid powder
- Sodium ascorbate
- Liposomal
- Liquid gel
- Capsules
- Ascorbic acid
- Buffered/Ester-C
- Buffered C
- Ester-C
- Buffered (sodium ascorbate)
- Calcium ascorbate· 70/100
Safety
Common side effects
- GI upset at high doses
- Diarrhea
Contraindications
- Hemochromatosis
- G6PD deficiency (IV)
Products containing Vitamin C
Top-scoring supplements in our catalog that list Vitamin C on the label. Each product is graded on Formulate's ingredient-level rubric — dose accuracy, form, transparency, and third-party testing.
Known interactions
Evidence notes
Essential vitamin with extensive research
Grade A: Multiple well-designed human trials support the main claims.
Cited research for Vitamin C
Clinical studies referenced across Formulate guides that mention vitamin c. Each links to the full study page with PubMed source + the guides that cite it.
Vitamin C compared head-to-head
Related in Vitamin
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Medical disclaimer. This page is educational and does not replace advice from a qualified healthcare provider. Individual needs and risks vary — consult a professional before starting, stopping, or combining supplements, especially if you are pregnant or nursing, taking medication, or managing a health condition.