Should I take 500 or 1000 mg of vitamin C?

Most people pick between 500mg and 1000mg by reading the label, not the research.

The research points somewhere else. In a controlled study at the National Institutes of Health, plasma and circulating cells saturated at 400mg a day, and higher doses were passed out in urine. Both of the numbers in the question sit above that line.

This page explains what actually happens in your body at each dose, which one is the safer default, and the three situations where 1000mg still earns its place.

Table of Contents

1. The Short Answer, and the Option the Question Leaves Out
2. What Happens in Your Body at 500mg
3. What Happens at 1000mg
4. Where Saturation Actually Sits: About 400mg a Day
5. Three Reasons People Reach for 1000mg
6. When 1000mg Is a Defensible Choice
7. The Variable the Number on the Label Cannot Show
8. Choosing a Format Once You Have Settled on a Number
9. Frequently Asked Questions
10. Conclusion
11. Research References

1. The Short Answer, and the Option the Question Leaves Out

If you are choosing only between those two numbers, 500mg is the better default for most healthy adults. It sits closer to the point where your body stops taking vitamin C in, and every measurable downside signal in the research attaches to the 1000mg level rather than the 500mg one.

But the question hides a third answer. The current RDA is 90mg a day for men and 75mg for women, and a group of vitamin C researchers concluded in 2012 that 200mg a day is the optimum intake for most adults. Even the Linus Pauling Institute, named after the man who popularised megadosing, recommends 400mg a day for generally healthy adults.

So the honest answer for most people is neither. Our full guide to daily vitamin C dosage works through where that 200mg to 400mg range comes from. What follows here is what separates the two doses you are actually weighing up.

2. What Happens in Your Body at 500mg

Vitamin C does not simply flood in. It is carried across the gut wall by transporters, and those transporters have a limit. In the landmark NIH study, seven volunteers lived in hospital for 4 to 6 months on a diet of under 5mg of vitamin C a day, then took controlled doses from 30mg up to 2,500mg. Bioavailability was complete for a single 200mg dose.

Above that, the picture changes. The same study found that at single doses of 500mg and higher, bioavailability declined and the absorbed amount was excreted. At 500mg you are already past the efficient part of the curve, but only just. The NIH puts overall absorption at roughly 70% to 90% at moderate intakes of 30mg to 180mg a day, and the decline from there is gradual rather than sudden.

The practical result is that a 500mg dose still delivers a useful amount, even though some of it is wasted. We cover the mechanism in more depth in our article on why most of a vitamin C dose is wasted.

3. What Happens at 1000mg

At a gram a day, two things happen at once. Less of the dose gets in, and more of what does get in comes back out. The NIH states plainly that at doses above 1g a day, absorption falls to less than 50% and unmetabolised ascorbic acid is excreted in the urine.

The blood levels barely move to match. Oral dosing of 1.25g a day produces mean peak plasma of about 135 micromoles per litre, roughly twice what you get from 200mg to 300mg a day. Doubling the tablet does not double the result, because pharmacokinetic modelling predicts even 3g every 4 hours would only reach about 220 micromoles per litre. The ceiling belongs to your physiology, not to the label.

There is also a marker worth knowing about. The NIH depletion study found that oxalate and urate excretion were elevated at 1000mg of vitamin C daily compared with lower doses. Oxalate is the main building block of the most common kind of kidney stone. That finding is the pivot point between the two doses in this question, and section 5 returns to what it does and does not mean. If you want the excretion side in detail, see what happens to the vitamin C you do not absorb.

4. Where Saturation Actually Sits: About 400mg a Day

The cleanest number in this whole field comes from a second NIH study, this one in 15 healthy young women who lived in hospital for around 186 days. Plasma and circulating cells saturated at 400mg daily, with urinary elimination of higher doses. Above 400mg, the tank is full.

Your immune cells fill up even sooner. The 1996 study found that neutrophils, monocytes and lymphocytes saturated at 100mg daily, holding concentrations at least 14 times higher than plasma. That is a useful corrective to the idea that a bigger tablet means better immune cover.

The Linus Pauling Institute puts steady-state plasma between 60 and 80 micromoles per litre at doses of 200mg to 400mg a day, with some individual variation. It also flags an honest limitation: those figures come from small groups of young, healthy volunteers, and nobody has established the equivalent for older adults or people under physical stress.

5. Three Reasons People Reach for 1000mg

Colds. This is the most common reason, and the evidence does not support it. A Cochrane review limited to trials of 0.2g a day or more found that across 29 trials and 11,306 participants, regular supplementation did not reduce how often people in the general population caught colds. It did shorten them by 8% in adults, about half a day on a typical cold. Taken only once symptoms start, there was no consistent effect at all.

More must mean better immunity. Section 4 covers why not: the immune cells are full at 100mg a day. You can read the wider picture in our article on what the research shows about vitamin C and immune function.

Worry about the safety ceiling. Here 1000mg is genuinely fine on its own terms. The Tolerable Upper Intake Level is 2000mg a day for adults in both the US and Canada, so a gram sits well inside it. But safe and useful are different questions. Two cohort studies attach their signals to roughly that dose: the Swedish kidney stone study, where users taking seven or more tablets a week had 2.23 times the risk and the typical Swedish supplement contained 1000mg, and a cohort of 24,593 Swedish women where a 25% higher risk of cataract extraction applied to those taking around 1000mg a day and not to those taking about 60mg. Neither study proves cause. Both point the same direction.

6. When 1000mg Is a Defensible Choice

None of the above makes a gram a bad decision for everyone. It makes it a decision that should have a reason behind it, and there are 3 reasons that hold up.

The clearest case is elevated need. People who smoke require 35mg a day more than people who do not, because of increased oxidative stress, and our article on why requirements are higher for smokers works through the detail. The Cochrane review also found one group where the effect was large rather than marginal: across 5 trials in 598 marathon runners, skiers and soldiers on subarctic exercise, vitamin C roughly halved cold incidence, with a pooled risk ratio of 0.48.

Low starting status is the other case. If your intake has been well below the 90mg RDA for a long stretch, you are not topping up a full tank. The same logic applies during recovery, when demand rises. What none of this supports is a permanent gram a day taken by a well-fed adult on the general principle that more is better.

Two groups should check with a doctor before settling on 1000mg: anyone with a kidney condition or a history of stones, and anyone with haemochromatosis, since chronic high doses could worsen iron overload in that condition. Anyone on regular medication should raise it too.

7. The Variable the Number on the Label Cannot Show

Everything above describes standard ascorbic acid. The number on the bottle tells you what went into the capsule, not what reaches your blood, and that gap widens at exactly the 2 doses in this question: below 50% of a 1g dose is absorbed at all.

That gap is what liposomal delivery targets. Wrapping vitamin C in a phospholipid shell is designed to get more of it past the limits described in section 2. A 2025 scoping review screened 321 studies and included 10 that compared the two forms directly. Nine of the ten showed higher plasma bioavailability for the liposomal form, with Cmax 1.2 to 5.4 times higher and AUC 1.3 to 7.2 times higher across doses ranging from 0.15g to 10g.

Three honest limits. The review noted industry funding or company-employed authors across the included studies, and that none of them measured how quickly the vitamin C was cleared. Better absorption in a blood test is well established; whether it changes health outcomes in someone already replete is not. And a better-absorbed format does not lift the 2000mg ceiling, which applies to vitamin C in any form. Whether liposomal delivery changes the oxalate picture at 1000mg has not been studied, so nobody should assume it does. Our comparison of the main vitamin C formats sets this alongside buffered and Ester-C options.

8. Choosing a Format Once You Have Settled on a Number

Once you have picked a daily amount, the remaining decision is what form to take it in and how much you trust the label. Two things are worth checking on any product: whether an independent lab has tested the batch, and what the ascorbic acid was made from. Almost all commercial vitamin C starts life as corn starch, which matters if you avoid corn.

Bio Absorb Nutraceuticals makes its liposomal vitamin C in two formats, Liposomal Vitamin C Liquid 1000mg (Corn-Free) and Liposomal Vitamin C Capsules 1000mg (Corn-Free), on the same formulation and the same allergen profile. Both are verified corn-free rather than assumed corn-free, and both are third-party tested every batch, so the label and the independent result describe the same product. Both are non-GMO, gluten-free, nut-free, dairy-free and vegan, made in a GMP-certified Canadian facility, and non-irradiated.

One thing the format does not change is the arithmetic in this article. The saturation point, the tolerable upper intake level and the cautions in section 6 apply to liposomal vitamin C the same way they apply to any other kind. Better absorption is a reason to take less, not a licence to take more.

The choice between them is about routine rather than chemistry. The liquid carries a natural orange flavour and mixes with water or juice, which makes it easy to split across the day. The capsules need no refrigeration and travel without fuss. Both carry a money-back guarantee, with no empty bottles to return.

For the figures that change over time, go to the source rather than an article: see current pricing and serving details for the liquid or the full product specification for the capsules. On sourcing, our article on why the source of ascorbic acid matters explains what corn-free verification involves.

Frequently Asked Questions

Is 1000mg of vitamin C a day too much?

No, it is well within the limits. The Tolerable Upper Intake Level is 2000mg a day for adults, so a gram is half of that. The issue is not safety so much as diminishing returns, since absorption falls below 50% above 1g a day.

Should I split 1000mg into two 500mg doses?

Splitting makes sense on the absorption maths, because a single 200mg dose is absorbed completely while 500mg and above is not. Two smaller doses spaced through the day each sit closer to the efficient part of the curve. Whether the extra absorbed milligrams change anything for a healthy adult who is already saturated is a separate question, and the answer there is probably not.

Does 500mg do anything that 1000mg does not?

Not in terms of benefit, but it avoids the markers that show up higher. Oxalate and urate excretion were elevated at 1000mg daily compared with lower doses. If the two doses do much the same thing at saturation, the lower one is the more conservative pick.

Do I need more than 500mg if I am getting over an illness?

Possibly, though the evidence is thinner than most people assume. Across 7 comparisons covering 3,249 cold episodes, vitamin C taken only after symptoms begin showed no consistent effect on duration or severity. Regular intake before you get ill is where the small 8% benefit sits.

Does liposomal vitamin C change which dose I should pick?

It changes how much of a given dose reaches your blood, not what your body can hold. A 2025 review found AUC 1.3 to 7.2 times higher for liposomal forms, but the 2000mg upper limit and the roughly 400mg saturation point apply to vitamin C in any form.

Can I just get this from food instead?

For the 200mg to 400mg range, largely yes. The NIH notes that five varied servings of fruit and vegetables can provide more than 200mg, with a single medium orange supplying about 70mg. Getting to 1000mg from food alone is considerably harder.

Conclusion

Between the two, 500mg is the safer default, because saturation arrives at around 400mg a day and the markers that rise at 1000mg have no matching benefit to justify them. Keep 1000mg for a reason rather than a habit: elevated requirements, low starting status, or recovery. If you want more of whatever dose you choose to actually reach your blood, Bio Absorb Nutraceuticals' corn-free liposomal vitamin C is built for that gap, and the complete guide to liposomal vitamin C covers how the delivery system works.

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). Found bioavailability complete for a single 200mg dose, declining at 500mg and above, with oxalate and urate excretion elevated at 1000mg daily compared with lower doses.
2. A new recommended dietary allowance of vitamin C for healthy young women. Proceedings of the National Academy of Sciences, Vol. 98, No. 17 (2001). Found plasma and circulating cells saturated at 400mg daily, with urinary elimination of higher doses.
3. Vitamin C pharmacokinetics: implications for oral and intravenous use. Annals of Internal Medicine, Vol. 140, No. 7 (2004). Established that oral dosing cannot push plasma vitamin C past a tightly controlled ceiling regardless of dose size.
4. Authors' Perspective: What is the Optimum Intake of Vitamin C in Humans? Critical Reviews in Food Science and Nutrition, Vol. 52, No. 9 (2012). Concluded that 200mg per day is the optimum dietary intake for the majority of the adult population.
5. Ascorbic acid supplements and kidney stone incidence among men: a prospective study. JAMA Internal Medicine, Vol. 173, No. 5 (2013). Found roughly double the kidney stone risk among ascorbic acid supplement users over 11 years of follow-up.
6. Vitamin C supplements and the risk of age-related cataract: a population-based prospective cohort study in women. American Journal of Clinical Nutrition, Vol. 91, No. 2 (2010). Found a 25% higher risk of cataract extraction among users of high-dose supplements but not low-dose multivitamins.
7. Do Liposomal Vitamin C Formulations Have Improved Bioavailability? A Scoping Review Identifying Future Research Directions. Basic & Clinical Pharmacology & Toxicology, Vol. 137, No. 1 (2025). Found 1.3 to 7.2-fold higher AUC for liposomal forms in nine of ten trials, while noting industry funding across all included studies.
8. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews, Issue 1 (2013). Found no reduction in cold incidence in the general population, an 8% reduction in duration for adults, and halved incidence in people under heavy short-term physical stress.
9. Vitamin C: Fact Sheet for Health Professionals. National Institutes of Health, Office of Dietary Supplements (2025). Source for the RDA, the 2000mg Tolerable Upper Intake Level, the smoking adjustment, and absorption falling below 50% above 1g a day.
10. Vitamin C and Pauling Recommendation. Linus Pauling Institute, Oregon State University (2024). Source for the 400mg daily recommendation and steady-state plasma concentrations of 60 to 80 micromoles per litre at 200mg to 400mg a day.
11. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Institute of Medicine, Food and Nutrition Board (2000). The source document establishing the 2000mg Tolerable Upper Intake Level for adults.

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.