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Ester-C 24 Hour Immune Support 1000 mg

NatureSmart
4.9
★ ★ ★ ★ ★
(13098 ratings)
Vitamin C 1000 mg
Flavonoid (mixture) 102 mg
Product Image
Score84
Convenient one-tablet Ester-C with a substantial dose and good value. The small proprietary bioflavonoid blend is supportive but not transparent.
How scoring works
Quantity:120 Tablet(s) • (120 servings)
Goals:
Immunity
General Health
Anti-Inflammatory Support
Skin Health
Vision Support

Score 84

Convenient one-tablet Ester-C with a substantial dose and good value. The small proprietary bioflavonoid blend is supportive but not transparent.
How scoring works
$14.12($0.11 per serving)
iHerb
$ 16.84
Walmart
$ 14.12
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Analysis

The 1000 mg Ester-C serving supplies a high amount of vitamin C in buffered calcium ascorbate form. It is well aligned with immune, antioxidant, and collagen-related support while potentially being gentler than unbuffered acid.

C-Sorb adds 102 mg of citrus bioflavonoids, providing a useful but secondary complement to vitamin C. Because the blend has no constituent breakdown, its specific flavonoid contribution cannot be assessed closely.

One tablet provides a full serving, and the 120-serving format is convenient for consistent daily use. The narrow formula is less suitable for people seeking broad vision or multisystem coverage.

Who is it for
  • Adults seeking one-tablet buffered vitamin C
  • People who prefer a simple formula
  • Users sensitive to plain ascorbic acid
Best for
  • Daily immune support
  • Antioxidant support
  • Convenient long-term use

Pros

  • 1000 mg buffered vitamin C
  • One-tablet serving
  • Lean active-ingredient list
  • Strong serving value

Cons

  • Bioflavonoid constituents are not disclosed
  • Only 102 mg of the complementary complex
  • Does not cover key nutrients used in broader vision formulas

Warnings

  • A 1000 mg vitamin C dose may cause digestive upset or loose stools
  • People with recurrent calcium oxalate stones should seek individualized advice before long-term high-dose use
  • The calcium ascorbate provides 110 mg of calcium per serving

Nutrient quality

92 Highest impact

Buffered calcium ascorbate provides a well-regarded form at a meaningful amount. Compatible citrus bioflavonoids add support without making the formula filler-heavy.

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Ingredient transparency

76 High impact

Active names and amounts are clearly stated, with no hidden proprietary dose. Complete intake directions and a full inactive-ingredient list are not included in the supplied data.

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Customer satisfaction

73 High impact

Supplied satisfaction metrics indicate a strong result with a meaningful response pool. Detailed experience themes are absent, so recurring complaints and real-world purpose fit remain uncertain.

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Value for money

97 Highest impact

Serving value appears favorable relative to the disclosed form and amount. The focused formula avoids low-value extras.

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Report analysis

Goals

Immunity
Immunity
Impact
Highest effect
A Goal FitA+ Strength of SupportC+ CoverageA+ Formula Quality
Vitamin C · 1000 mg

Buffered calcium ascorbate provides a strong vitamin C amount for antioxidant protection and immune-cell support. Clear calcium disclosure and a meaningful bioflavonoid complex strengthen the focused formula.

The tablet is streamlined and may be easier on the stomach than ordinary ascorbic acid. Its main limitation is narrow pathway coverage because it does not add zinc, vitamin D, or barrier-focused nutrients.

Study evidence
Vitamin C Supportive 53 studies
General Health
General Health
Impact
Highest effect
A- Goal FitA+ Strength of SupportC+ CoverageA Formula Quality
Vitamin C · 1000 mg

Buffered calcium ascorbate delivers a substantial vitamin C amount with good label clarity. The form may be easier on the stomach than plain ascorbic acid.

Citrus bioflavonoids complement the focused antioxidant formula without excessive complexity. Coverage is still narrow because the product does not address other common nutrient gaps.

Study evidence
Vitamin C Supportive 56 studies
Anti-Inflammatory Support
Anti-Inflammatory Support
Impact
Highest effect
B Goal FitA Strength of SupportC+ CoverageA Formula Quality
Vitamin C · 1000 mg

The 1,000 mg buffered vitamin C amount provides substantial antioxidant support relevant to oxidative inflammatory stress. Citrus bioflavonoids add a complementary but secondary antioxidant pathway.

Ester-C offers a well-disclosed, stomach-friendly form with a meaningful single-tablet serving. The vitamin C amount may still cause loose stools in sensitive users, particularly when combined with other high-dose vitamin C sources.

Study evidence
Vitamin C Supportive 50 studies
Skin Health
Skin Health
Impact
High effect
B- Goal FitA Strength of SupportC CoverageB+ Formula Quality
Vitamin C · 1000 mg

Buffered vitamin C supplies a substantial amount needed for normal collagen synthesis and antioxidant defense. The disclosed mineral ascorbate form may be gentler on the stomach than plain ascorbic acid.

The focused formula provides strong depth for one nutrient but does not supply collagen, ceramides, or direct hydration support. Supporting bioflavonoids add antioxidant context without making the product comprehensive.

Study evidence
Vitamin C Supportive 53 studies
Vision Support
Vision Support
Impact
High effect
D+ Goal FitA Strength of SupportD CoverageA- Formula Quality
Vitamin C · 1000 mg

Vitamin C contributes retinal antioxidant protection but cannot cover macular pigment or structural needs alone. Vitamin C is part of established ocular nutrient combinations, though standalone evidence is limited for broad vision outcomes.

The vitamin C amount is substantial and the bioflavonoid complex is meaningfully disclosed. Buffered Ester-C and the citrus complex are clearly identified with exact amounts.

Study evidence
Vitamin C Disputed 24 studies

Ingredients

IngredientAmount per serving
Vitamin C (Ester-C Calcium Ascorbate)
 1000 mg
Calcium (Ester-C Calcium Ascorbate)
 110 mg
C-Sorb Citrus Bioflavonoid Complex
102 mg
Gluten Free Adults 18–50 Dairy Free Sugar Free Vegetarian
Report overview
Vitamin C (Ester-C Calcium Ascorbate) · 1000 mg OverallScore96
A- Active Ingredient Quality & BioavailabilityA+ Dose, Safety & Label TransparencyA+ Value

Ester-C supplies a buffered, pH-neutral form designed for digestive comfort. The 1000 mg serving sits within the optimal range, and the listed formula avoids sugar-based fillers and artificial colors. Cost per effective amount is exceptionally economical for the form.

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Loading alternative details
87 Performance

Ester-C with Citrus Bioflavonoids

American Health
<p>A full Ester-C amount and substantial citrus bioflavonoid complex preserve the original’s key buffered profile. The supplied quality and goal evidence is slightly more balanced, although the individual flavonoids are not broken out.</p>
86 Performance

C

Swanson
<p>A full amount of calcium ascorbate plus a clearly stated citrus bioflavonoid amount creates a focused buffered formula. The more concise active profile is easier to interpret than the original, though it supplies less total bioflavonoid material.</p>
89 Performance

C-500 Calcium Ascorbate-C

NOW
<p>A clearly stated calcium ascorbate amount and a small citrus bioflavonoid addition make this a focused buffered option. The supplied quality evidence is stronger, but the vitamin C and flavonoid amounts are lower than in the original.</p>
84 Budget

Ester-C 500 mg With Citrus Bioflavoinds

American Health
<p>The same buffered vitamin C amount and broad citrus bioflavonoid profile are provided at a lower serving cost. Ingredient fit is nearly identical to the original, making the smaller package a more economical way to obtain the same core formula.</p>
89 Budget

Pure Buffered Calcium Ascorbate

NOW
<p>Buffered calcium ascorbate supplies a substantial vitamin C amount at a lower serving cost. Citrus bioflavonoids are omitted, but the buffered form preserves the original formula’s main stomach-comfort advantage while reducing cost.</p>
87 Budget

100% Pure Vitamin C Powder

Swanson Premium Brand
<p>Single-ingredient ascorbic acid powder provides a full vitamin C amount at a lower serving cost. It lacks buffered calcium ascorbate and citrus bioflavonoids, so it favors economy and dose simplicity over the original’s broader profile.</p>
86 Value

Buffered Vitamin C + Citrus Bioflavonoids

Jarrow Formulas
<p>Buffered calcium ascorbate and a substantial bioflavonoid amount provide a useful balance of ingredient fit and value. The vitamin C amount is lower than in the original, while the flavonoid coverage remains meaningful.</p>
80 Value

Supreme C Complex

Swanson Premium Brand
<p>Vitamin C, a substantial citrus bioflavonoid complex, and added rutin create broad flavonoid support with favorable value. Ascorbic acid replaces the original’s buffered form, so stomach comfort may be a more important trade-off.</p>
87 Value

Pure Buffered Magnesium Ascorbate

NOW
<p>Buffered magnesium ascorbate supplies a substantial vitamin C amount with favorable value and adds magnesium from the same compound. It omits citrus bioflavonoids, but keeps a buffered mineral ascorbate form while lowering formula complexity.</p>
Report alternatives

Sources

Published studies used for the product analysis and the top-ranked studies for each ingredient and goal.

  1. Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis.
    Bjelakovic G; Nikolova D; Gluud LL; Simonetti RG; Gluud C · JAMA · 2007
    Meta-analysis232,606 participants68 studies pooledGeneral Health forVitamin C
  2. Vitamin C intake and multiple health outcomes: an umbrella review of systematic reviews and meta-analyses.
    Xu K; Peng R; Zou Y; Jiang X; Sun Q; Song C · International journal of food sciences and nutrition · 2022
    Meta-analysis76 studies pooledGeneral Health forVitamin C
  3. Vitamin C supplementation in kidney failure: effect on uraemic symptoms.
    Singer RF · Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association · 2011
    Randomized trial99 participantsGeneral Health forVitamin C
  4. Vitamin C and contribution to the normal function of the immune system: evaluation of a health claim pursuant to Article 14 of Regulation (EC) No 1924/2006.
    EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) · EFSA journal. European Food Safety Authority · 2026
    Guideline / consensusImmunity forVitamin C
  5. Effect of Vitamin C Supplements on Respiratory Tract Infections: A Systematic Review and Meta-Analysis.
    Keya TA; Leela A; Fernandez K; Habib N; Rashid M · Current reviews in clinical and experimental pharmacology · 2022
    Meta-analysis10 studies pooledImmunity forVitamin C
  6. Enhanced Vitamin C Delivery: A Systematic Literature Review Assessing the Efficacy and Safety of Alternative Supplement Forms in Healthy Adults.
    Calder PC; Kreider RB; McKay DL · Nutrients · 2025
    Systematic review13 studies pooledImmunity forVitamin C
  7. Dietary nutrient intakes and skin-aging appearance among middle-aged American women.
    Cosgrove MC; Franco OH; Granger SP; Murray PG; Mayes AE · The American journal of clinical nutrition · 2007
    Cross-sectional study4,025 participantsSkin Health forVitamin C
  8. Double-blind, half-face study comparing topical vitamin C and vehicle for rejuvenation of photodamage.
    Fitzpatrick RE; Rostan EF · Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.] · 2002
    Non-randomized trial10 participantsSkin Health forVitamin C
  9. Vitamin C and postoperative outcomes following mandibular third molar extraction: a randomized split-mouth study.
    Demirel M; Aktas A; Kizil M; Yalcin N · Oral surgery, oral medicine, oral pathology and oral radiology · 2026
    Randomized trial56 participantsSkin Health forVitamin C
  10. Efficacy of Vitamin C as Glucocorticoid Substitute for Reducing Pain and Inflammation After Total Hip Arthroplasty: A Randomized Controlled Trial.
    Jiang W; Xu H; Jiang X; Zhan Y; Ju Y; Xie J; Huang Z; Huang Q; Pei F · The Journal of bone and joint surgery. American volume · 2025
    Randomized trial107 participantsAnti-Inflammatory Support forVitamin C
  11. The Impact of Vitamin C on Analgesic, Anti-inflammatory, and Hemostatic Outcomes After Total Hip and Knee Arthroplasty: A Systematic Review and Meta-Analysis.
    Moftakhari Hajimirzaei S; Bagherzadeh Cham M; Dolikhani M; Tabatabaee SM; Ebrahimpour A · The archives of bone and joint surgery · 2026
    Meta-analysis1,162 participants10 studies pooledAnti-Inflammatory Support forVitamin C
  12. The impact of vitamin C supplementation on the perioperative outcomes after total hip and knee arthroplasty: a systematic review and meta-analysis.
    Liu X; Guo J; Li Y; Yang Y; Liu M; Gao Q; Yang Y; Wu X; Yue C · BMC musculoskeletal disorders · 2026
    Meta-analysis852 participants8 studies pooledAnti-Inflammatory Support forVitamin C
  13. Therapeutic Impact of Ascorbic Acid on Oral and Periodontal Tissues: A Systematic Literature Review.
    Ruzijevaite G; Acaite E; Jagelaviciene E · Medicina (Kaunas, Lithuania) · 2025
    Systematic review811 participants17 studies pooledAnti-Inflammatory Support forVitamin C
  14. Oral vitamin C administration reduces early recurrence rates after electrical cardioversion of persistent atrial fibrillation and attenuates associated inflammation.
    Korantzopoulos P; Kolettis TM; Kountouris E; Dimitroula V; Karanikis P; Pappa E; Siogas K; Goudevenos JA · International journal of cardiology · 2005
    Randomized trial44 participantsAnti-Inflammatory Support forVitamin C
  15. Dietary intake and blood concentrations of antioxidants and the risk of cardiovascular disease, total cancer, and all-cause mortality: a systematic review and dose-response meta-analysis of prospective studies.
    Aune D; Keum N; Giovannucci E; Fadnes LT; Boffetta P; Greenwood DC; Tonstad S; Vatten LJ; Riboli E; Norat T · The American journal of clinical nutrition · 2019
    Meta-analysis69 studies pooledGeneral Health forVitamin C
  16. Scientific Opinion on the substantiation of a health claim related to vitamin C and increasing non haem iron absorption pursuant to Article 14 of Regulation (EC) No 1924/2006.
    EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) · EFSA journal. European Food Safety Authority · 2026
    Guideline / consensusGeneral Health forVitamin C
  17. Vitamin C Depletion and All-Cause Mortality in Renal Transplant Recipients.
    Sotomayor CG; Eisenga MF; Gomes Neto AW; Ozyilmaz A; Gans ROB; Jong WHA; Zelle DM; Berger SP; Gaillard CAJM; Navis GJ; Bakker SJ · Nutrients · 2018
    Cohort study598 participantsGeneral Health forVitamin C
  18. Associations of Serum Biomarkers of Fruit and Vegetable Intake With the Risk of Cause-Specific Mortality and All-Cause Mortality: A National Prospective Cohort Study.
    Pu L; Zhang R; Wang X; Zhao T; Sun H; Han L · Frontiers in nutrition · 2022
    Cohort study12,530 participantsGeneral Health forVitamin C
  19. Relation between plasma ascorbic acid and mortality in men and women in EPIC-Norfolk prospective study: a prospective population study. European Prospective Investigation into Cancer and Nutrition.
    Khaw KT; Bingham S; Welch A; Luben R; Wareham N; Oakes S; Day N · Lancet (London, England) · 2001
    Cohort study19,496 participantsGeneral Health forVitamin C
  20. Therapeutic effects of high-dose vitamin C supplementation in patients with COVID-19: a meta-analysis.
    Sun L; Zhao JH; Fan WY; Feng B; Liu WW; Chen RQ; Ban C; Dang AG; Wang M; Luo KT; Zhou GY; Yu FF; Ba Y · Nutrition reviews · 2024
    Meta-analysis2,334 participants14 studies pooledImmunity forVitamin C
  21. Effect of micronutrient supplements on influenza and other respiratory tract infections among adults: a systematic review and meta-analysis.
    Abioye AI; Bromage S; Fawzi W · BMJ global health · 2021
    Meta-analysisImmunity forVitamin C
  22. New evidence for antioxidant properties of vitamin C.
    Vojdani A; Bazargan M; Vojdani E; Wright J · Cancer detection and prevention · 2001
    Randomized trial20 participantsImmunity forVitamin C
  23. Evaluation of the anti-wrinkle effect of an ascorbic acid-loaded dissolving microneedle patch via a double-blind, placebo-controlled clinical study.
    Lee C; Yang H; Kim S; Kim M; Kang H; Kim N; An S; Koh J; Jung H · International journal of cosmetic science · 2017
    Randomized trial23 participantsSkin Health forVitamin C
  24. Comparative Study on the Outcome of Periorbital Wrinkles Treated with Laser-Assisted Delivery of Vitamin C or Vitamin C Plus Growth Factors: A Randomized, Double-blind, Clinical Trial.
    Machado BHB; Frame J; Zhang J; Najlah M · Aesthetic plastic surgery · 2021
    Randomized trial149 participantsSkin Health forVitamin C
  25. Randomized trial of topical ascorbic acid in DMSO versus imiquimod for the treatment of basal cell carcinoma.
    Burke B; Bailie JE · Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie · 2022
    Randomized trial25 participantsSkin Health forVitamin C
  26. Vitamin C improves healing of foot ulcers: a randomised, double-blind, placebo-controlled trial.
    Gunton JE; Girgis CM; Lau T; Vicaretti M; Begg L; Flood V · The British journal of nutrition · 2022
    Randomized trial16 participantsSkin Health forVitamin C
  27. Role of Oral Vitamin 'C' on Astigmatic Errors in Phacoemulsification.
    Mohan S; Sah K; Khattri M; Ahmad L; Sachan SK · Current eye research · 2021
    Randomized trial400 participantsVision Support forVitamin C
  28. Ascorbic acid metabolites are involved in intraocular pressure control in the general population.
    Hysi PG; Khawaja AP; Menni C; Tamraz B; Wareham N; Khaw KT; Foster PJ; Benet LZ; Spector TD; Hammond CJ · Redox biology · 2019
    Observational studyVision Support forVitamin C
  29. Nutritional modulation of cataract.
    Weikel KA; Garber C; Baburins A; Taylor A · Nutrition reviews · 2014
    Narrative reviewVision Support forVitamin C
  30. Dietary n-3 Fatty Acid, α-Tocopherol, Zinc, vitamin D, vitamin C, and β-carotene are Associated with Age-Related Macular Degeneration in Japan.
    Aoki A; Inoue M; Nguyen E; Obata R; Kadonosono K; Shinkai S; Hashimoto H; Sasaki S; Yanagi Y · Scientific reports · 2017
    Case-control study530 participantsVision Support forVitamin C
  31. Adherence to a Mediterranean diet, lifestyle and age-related macular degeneration: the Coimbra Eye Study - report 3.
    Raimundo M; Mira F; Cachulo MDL; Barreto P; Ribeiro L; Farinha C; Laíns I; Nunes S; Alves D; Figueira J; Merle BM; Delcourt C; Santos L; Silva R · Acta ophthalmologica · 2019
    Case-control study883 participantsVision Support forVitamin C