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Vitamin C

Supplement vitamin immuneskin & hair
Aka: ascorbic acid, L-ascorbate, Gold C, Redoxon
Brands seen in Singapore: California Gold Nutrition, Life Extension, NOW Foods, Sunlipid, NeoCell
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Collagen formation for skin · normal immune function
When to take
No timing rule given
Take with
Ascorbic acid absorbs as well as the vitamin C in food
Pros & cons
Pros
  • RDA 90 mg (men) · 75 mg (women); smokers +35 mg a day
  • Humans can't make vitamin C — an essential nutrient
  • Colds: modestly shorter — 8% adults, 14% children
Cons
  • Above 1 g a day, absorption falls below 50%
  • High doses: diarrhea, nausea, cramps from unabsorbed c
  • Doesn't cut cold risk in the general population
Sources
  1. NIH ODS — Vitamin C Fact Sheet for Health Professionals (updated July 31, 2025) — Introduction + Table 1 RDAs (19+ years row: male · female · pregnancy · lactation) + smokers note · read 2026-08-27
    what it says
    “Humans, unlike most animals, are unable to synthesize vitamin C endogenously, so it is an essential dietary component … 19+ years 90 mg 75 mg 85 mg 120 mg … require 35 mg/day more vitamin C”
  2. NIH ODS — Vitamin C Fact Sheet for Health Professionals (updated July 31, 2025) — Sources of Vitamin C: Dietary supplements · read 2026-08-27
    what it says
    “Supplements typically contain vitamin C in the form of ascorbic acid, which has equivalent bioavailability to that of naturally occurring ascorbic acid in foods, such as orange juice and broccoli”
  3. NIH ODS — Vitamin C Fact Sheet for Health Professionals (updated July 31, 2025) — Introduction (absorption) · read 2026-08-27
    what it says
    “Approximately 70% to 90% of vitamin C is absorbed at moderate intakes of 30 to 180 milligrams (mg)/day. However, at doses above 1 gram (g)/day, absorption falls to less than 50%”
  4. NIH ODS — Vitamin C Fact Sheet for Health Professionals (updated July 31, 2025) — Table 3 ULs (19+ years row) + Health Risks from Excessive Vitamin C · read 2026-08-27
    what it says
    “19+ years 2,000 mg 2,000 mg 2,000 mg 2,000 mg … The most common complaints are diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances due to the osmotic effect of unabsorbed vitamin C in the gastrointestinal tract”
  5. NIH ODS — Vitamin C Fact Sheet for Health Professionals (updated July 31, 2025) — Health Risks from Excessive Vitamin C (kidney stones; hemochromatosis) · read 2026-08-27
    what it says
    “High vitamin C intakes … could contribute to the formation of kidney stones, especially in individuals with renal disorders … in individuals with hereditary hemochromatosis, chronic consumption of high doses of vitamin C could exacerbate iron overload”
  6. NIH ODS — Vitamin C Fact Sheet for Health Professionals (updated July 31, 2025) — Interactions with Medications (Chemotherapy and radiation; Statins and niacin) · read 2026-08-27
    what it says
    “undergoing chemotherapy or radiation should consult with their oncologist … Vitamin C, in combination with other antioxidants, may attenuate the increase in high-density lipoprotein levels that result from taking combination niacin/simvastatin (Zocor) therapy”
  7. NIH ODS — Vitamin C Fact Sheet for Health Professionals (updated July 31, 2025) — Vitamin C and Health: Common cold · read 2026-08-27
    what it says
    “Prophylactic use of vitamin C did not significantly reduce the risk of developing a cold in the general population … the use of prophylactic vitamin C modestly reduced cold duration by 8% in adults and 14% in children”
  8. FDA — Daily Value on the Nutrition and Supplement Facts Labels, Reference Guide: Daily Values for Nutrients (content current as of 03/05/2024) · read 2026-08-27
    what it says
    “DVs are the recommended amounts of nutrients to consume or not to exceed each day … Vitamin C 90mg”
  9. HSA Singapore — Health Supplements Guidelines GL-CHPB-3-001 Rev. No. 020 (January 2026), s4.8 general-adult limits, Table 4 Vitamins Limits + List of Health Claims rows 19 + 70 · read 2026-08-27
    what it says
    “Table 4: Vitamins Limits … Vitamin C 1000mg … Contribute to normal collagen formation for normal function of skin • Vitamin C … Help in the normal function of the immune system • Folic acid, vitamin A, B6, B12, C, D”
  10. HSA Singapore — Guidelines on Prohibited and Restricted Ingredients in Health Supplements and Traditional Medicines, GL-CHPB-1-012 Rev. 001 (October 2025), Annex A row 113 · read 2026-08-27
    what it says
    “113. Vitamin C Restricted use in HS and TM Maximum Daily Dose When for oral use by general adult population, the maximum recommended daily dose should not provide more than 1000mg”
  11. iHerb Singapore — Vitamin C category, default order (SGD pricing) · read 2026-08-27
    what it says
    “California Gold Nutrition, Gold C®, USP Grade Vitamin C, 1,000 mg … Life Extension, Glutathione, Cysteine & C … NOW Foods, Liposomal Vitamin C … Sunlipid, Liposomal Vitamin C with MCT Oil … NeoCell, Grassfed Collagen Peptides + Vitamin C & Biotin”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.