Vitamin C Dosage: How Much Should You Take Per Day?

The recommended daily amount of vitamin C is 90mg for men and 75mg for women — and there is a serious argument in the research literature that this number is roughly half of what it should be.

That gap is not academic. NHANES data puts 41.8% of US adults below sufficient blood levels, and the dose most people reach for — 1,000mg — is one the gut absorbs less than half of.

This guide covers the three numbers that matter — 90mg, 200mg and 2,000mg — and how to find your own vitamin C dosage.

Table of Contents

1. What the Official Vitamin C Dosage Guidelines Recommend
2. Why Researchers Argue the RDA Is a Floor, Not a Target
3. What Actually Happens When You Take 1,000mg
4. Vitamin C Dosage by Situation: How Much Should You Take?
5. The Upper Limit — and Who Should Stay Well Below It
6. Timing: Splitting Doses and When to Take Them
7. When Delivery Format Changes the Dosing Maths
8. Frequently Asked Questions
9. Conclusion
10. Research References

1. What the Official Vitamin C Dosage Guidelines Recommend

The National Institutes of Health sets the Recommended Dietary Allowance at 90mg per day for adult men and 75mg per day for adult women. People who smoke need an additional 35mg per day, because smoking accelerates oxidative turnover of the vitamin. The same Dietary Reference Intake values are used in Canada.

The RDA is not a target for optimal health. It is the intake estimated to meet the requirements of 97–98% of healthy people — a floor set to prevent deficiency, not a ceiling set to maximise anything. That distinction explains most of the confusion about how much to take.

Average intakes in the US already sit above the RDA, at 105.2mg/day for adult men and 83.6mg/day for adult women. Yet averages hide a wide spread, and the 2,000mg/day tolerable upper intake level leaves a very large gap between "enough to avoid scurvy" and "as much as is safe."

2. Why Researchers Argue the RDA Is a Floor, Not a Target

The most influential dosing work in this field is a 1996 depletion–repletion study in which seven hospitalised volunteers were taken down to under 5mg of vitamin C daily and then given escalating doses from 30mg up to 2,500mg. The steep part of the dose–response curve sat between 30mg and 100mg daily, and bioavailability was complete for a single 200mg dose.

Building on that pharmacokinetic work, a group of vitamin C researchers argued in a 2012 perspective paper that 200mg/day is the more defensible target for healthy adults. At that intake, plasma reaches roughly 70 µmol/L — the range of 64–85.2 µmol/L where observational studies tend to show the strongest associations with health outcomes.

The Linus Pauling Institute describes plasma reaching steady state at 60–80 µmol/L on doses of 200–400mg/day in healthy young adults. It is worth being clear about what this evidence does and does not establish: it shows where blood levels plateau, not that every person taking 200mg will experience a measurable health improvement over one taking 90mg.

3. What Actually Happens When You Take 1,000mg

Vitamin C absorption is not linear. The NIH reports that roughly 70–90% is absorbed at moderate intakes of 30–180mg per day, but absorption falls below 50% at doses above 1 gram per day. The transporters that move vitamin C across the gut wall are saturable, and once they are saturated, additional milligrams largely pass through.

The 1996 pharmacokinetic data makes the same point from the excretion side: at single doses of 500mg and above, bioavailability declined and the absorbed amount was simply excreted in urine. Six of the seven volunteers excreted no vitamin C at all until the 100mg dose.

• At 200mg in a single dose, absorption is essentially complete
• Above 500mg in a single dose, a growing share is absorbed and then excreted
• Above 1,000mg per day, less than half of what you swallow is absorbed at all

This is the central reason a 1,000mg tablet does not deliver 1,000mg to your tissues, and it is covered in detail in our guide to why most of a vitamin C dose is wasted.

4. Vitamin C Dosage by Situation: How Much Should You Take?

There is no single correct vitamin C dosage, but there is a defensible range. For most healthy adults eating a reasonable diet, an intake somewhere between the 90mg RDA and the 200mg research target is well supported, and doses in the 500–1,000mg/day range appear in a large share of the clinical literature without safety concerns in healthy people.

Circumstances shift the number upward:

• People who smoke need at least 35mg/day more, and 60.8% of smokers show insufficient vitamin C status compared with 34.8% of non-smokers — covered in why smokers have higher vitamin C requirements
• People eating few fruits and vegetables, where diet alone rarely clears 200mg/day — see the highest food sources of vitamin C
• Older adults and people under sustained physical or oxidative stress, whose status tends to run lower than the 50–70 µmol/L range NHANES classes as adequate

A practical approach is to start at the low end of whatever range applies, hold it for two to three weeks, and adjust only if there is a reason to. Because plasma plateaus at 60–80 µmol/L regardless, pushing far beyond 400mg/day changes blood levels much less than the label suggests.

5. The Upper Limit — and Who Should Stay Well Below It

The tolerable upper intake level for adults is 2,000mg/day. It was set specifically to avoid diarrhoea and gastrointestinal disturbance at high supplemental intakes, which are the most common and most reversible adverse effects.

Kidney stones are the more serious question. An 11-year prospective study of 23,355 Swedish men found that ascorbic acid supplement users had roughly double the incidence of kidney stones, with a relative risk of 1.95 (95% CI 1.35–2.81) and a dose–response trend: 1.66 for fewer than seven tablets a week and 2.23 for seven or more, on tablets of about 1,000mg. That finding is in men only and has not been shown in women.

Caution is warranted rather than alarm, and it is not evenly distributed. The Linus Pauling Institute suggests those predisposed to stone formation consider avoiding supplemental doses at or above 1 gram per day. Talk to a physician before supplementing at that level if you have kidney disease, a history of stones, or haemochromatosis or another iron-overload condition. The full picture is in vitamin C side effects and the upper limit. The megadose case is examined separately in high-dose vitamin C.

6. Timing: Splitting Doses and When to Take Them

Because a single 200mg dose is absorbed essentially completely while a single 1,000mg dose is not, splitting your vitamin C dosage across the day extracts more from the same total. Two 250mg doses will generally deliver more absorbed vitamin C than one 500mg dose, and the effect grows as the total rises.

Vitamin C is water-soluble and does not require food for absorption, though taking it with a meal is a common way to reduce the stomach discomfort some people notice at doses above 1,000mg. There is no strong evidence favouring morning over evening.

Consistency matters more than timing. The 2013 Cochrane review of 29 trial comparisons in 11,306 participants found that regular supplementation of 0.2g/day or more shortened colds by 8% in adults and 14% in children, while doing little for incidence in the general population (risk ratio 0.97). In people under heavy short-term physical stress — marathon runners, skiers, soldiers — five trials in 598 participants found the risk roughly halved (risk ratio 0.48).

7. When Delivery Format Changes the Dosing Maths

Everything above assumes standard ascorbic acid, where absorption efficiency drops as the dose climbs. Liposomal delivery encapsulates vitamin C in a phospholipid shell, and a 2025 scoping review found AUC improvements of 1.3–7.2× over non-liposomal forms in 9 of 10 trials. The UK Committee on Toxicity's review of six human trials reported a comparable spread.

The honest framing matters here. The absorption advantage is well documented across those 10 trials; whether it produces better clinical outcomes in people who are already replete has not been established, and the COT review of 6 human trials explicitly noted the absence of health-outcome data. Better absorption is a reason to expect a given dose to go further, not a reason to expect a different result.

Bio Absorb Nutraceuticals makes its Liposomal Vitamin C in a GMP-certified Canadian facility, in two formats: a liquid that mixes with water or juice, and capsules that need no refrigeration and travel well. For anyone working out a dose, the practical difference is that the liquid allows finer adjustment across the day — useful if you are splitting a total rather than taking it all at once — while the capsules are simpler to keep consistent. For most people consistency matters more than precision, which is an argument for whichever format you will actually remember to take.

Both are verified corn-free, which is unusual in a category where most ascorbic acid is corn-derived. That distinction is irrelevant to most people and decisive for a few: for anyone with a corn allergy or sensitivity, it is often the difference between tolerating a daily supplement and giving up on one. Both are also non-GMO, gluten-free, nut-free, dairy-free and vegan, and every batch is third-party tested, so the label and the independent result describe the same product. Both are covered by a money-back guarantee.

The delivery system is what ties this back to dosing. If absorption efficiency is the thing limiting a standard dose, then the format changes the arithmetic more than the number on the front of the bottle does. See current serving details for the liquid or the full product specification for the capsules. Background on the delivery system is in our complete guide to liposomal vitamin C.

Frequently Asked Questions

Is 1,000mg of vitamin C a day too much?

It is well below the 2,000mg/day tolerable upper intake level and is used routinely in clinical studies, so it is not unsafe for most healthy adults. It is, however, inefficient: absorption drops below 50% above 1 gram per day, so much of it is excreted. Men with a history of kidney stones should discuss doses at this level with a physician.

Can I take vitamin C on an empty stomach?

Yes — it is water-soluble and does not need dietary fat to be absorbed. Some people find doses above 1,000mg cause stomach upset or loose stools, which is the effect the 2,000mg upper limit was set to prevent, and taking it with food usually helps.

Do I really need more vitamin C if I smoke?

Yes. The NIH adds 35mg/day to the RDA for smokers, and NHANES data shows 60.8% of smokers at insufficient levels versus 34.8% of non-smokers, with only 14.7% reaching saturating levels. In practice most smokers need considerably more than the 35mg minimum to close that gap.

Does liposomal vitamin C mean I can take a smaller dose?

Possibly, though the honest answer is that nobody has established the equivalence precisely. The 1.3–7.2× AUC range reported in the 2025 scoping review is wide, and it describes blood exposure rather than clinical effect. Treat it as a reason a given dose may go further, not as a fixed conversion factor.

What happens if I take too much vitamin C?

The most common effects are gastrointestinal — diarrhoea, cramping, nausea — and they resolve when the dose comes down. The longer-term concern is oxalate: the 1996 pharmacokinetic study found oxalate and urate excretion elevated at 1,000mg daily compared with lower doses, which is the mechanism behind the kidney stone signal.

Can I get enough vitamin C from food alone?

You can clear the 90mg RDA from food without difficulty, but reaching the 200mg research target consistently is harder — which is part of why 41.8% of US adults still fall short of adequate status. Diet first is sound advice; supplementation is a reasonable way to close a persistent gap.

Conclusion

The 90mg RDA prevents deficiency, the 200mg mark is where the pharmacokinetic evidence points for healthy adults, and the 2,000mg ceiling is where caution begins — but the right vitamin C dosage is decided by absorption, not by the number on the label. If you want that dose to go further, see current pricing and serving details for Bio Absorb's Liposomal Vitamin C.

Research References

1. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proceedings of the National Academy of Sciences, Vol. 93, No. 8 (1996), pp. 3704–3709. Depletion–repletion study in seven volunteers establishing that bioavailability is complete at a single 200mg dose and declines from 500mg upward, with oxalate and urate excretion elevated at 1,000mg daily.
2. Authors' Perspective: What is the Optimum Intake of Vitamin C in Humans? Critical Reviews in Food Science and Nutrition, Vol. 52, No. 9 (2012), pp. 815–829. Argues for 200mg/day as the optimum intake for healthy adults, the dose bringing plasma to approximately 70 µmol/L.
3. Do Liposomal Vitamin C Formulations Have Improved Bioavailability? A Scoping Review Identifying Future Research Directions. Basic & Clinical Pharmacology & Toxicology, Vol. 137 (2025), article e70067. Reports AUC improvements of 1.3–7.2× for liposomal over non-liposomal vitamin C in 9 of 10 trials, while noting the absence of clinical outcome data.
4. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews (2013). Across 29 comparisons in 11,306 participants, regular supplementation of 0.2g/day or more shortened colds by 8% in adults and 14% in children, halved risk under heavy physical stress (RR 0.48), but did not reduce incidence in the general population (RR 0.97).
5. Ascorbic Acid Supplements and Kidney Stone Incidence Among Men: A Prospective Study. JAMA Internal Medicine, Vol. 173, No. 5 (2013), pp. 386–388. Eleven-year follow-up of 23,355 men finding a relative risk of 1.95 for kidney stones among ascorbic acid supplement users, with a dose–response trend.
6. Insufficient Vitamin C Levels among Adults in the United States: Results from the NHANES Surveys, 2003–2006. Nutrients, Vol. 13, No. 11 (2021), article 3910. Found 41.8% of US adults at insufficient vitamin C levels, rising to 60.8% among smokers.
7. Vitamin C — Fact Sheet for Health Professionals. National Institutes of Health, Office of Dietary Supplements (2025). Source for the 90mg/75mg RDA, the 35mg/day smoker increment, the 2,000mg tolerable upper intake level, and absorption of 70–90% at 30–180mg/day falling below 50% above 1g/day.
8. Vitamin C — Micronutrient Information Center. Linus Pauling Institute, Oregon State University. Source for plasma steady state of 60–80 µmol/L at 200–400mg/day, complete absorption at doses up to 200mg, and the kidney stone caution at intakes of 1g/day or above.
9. Discussion paper on novel formulations of supplement compounds designed to increase oral bioavailability — Case study: liposomal vitamin C. UK Committee on Toxicity ([publication year not confirmed]). Review of six human trials reporting comparable AUC and Cmax increases for liposomal vitamin C, and noting the absence of data on clinical health outcomes.

About the Author

David Kimbell is a health writer, digital entrepreneur and former aerospace engineer, based in Ottawa, Canada. He loves translating complex science into clear, actionable guidance for consumers seeking evidence-based solutions.

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Important Disclaimers

Medical Disclaimer: This article provides educational information only and is not intended as medical advice. Always consult with a qualified healthcare provider before starting any new supplement, especially if you have existing health conditions, take medications, or are pregnant or nursing.

FDA/Health Canada Statement: These statements have not been evaluated by the Food and Drug Administration or Health Canada. This product is not intended to diagnose, treat, cure, or prevent any disease.