How much vitamin C should I take daily?
Take 500 mg to 1,000 mg twice a day, morning and afternoon to maximise an increased blood level for much of the day. Vitamin C is water soluble, and much is excreted within hours above 500mg or 1,000 mg under normal conditions so it is better to spread your daily dose throughout the day. There is a substantial case for a daily intake of 500 mg reducing cardiovascular disease. During times of high viral exposure it would be sensible to take 2,000 mg spread across the day, or whatever you can tolerate without loose bowels. This is called your ‘bowel tolerance’ level. However, this is not usually an issue and only occurs in some people when doses reach over 3 grams.
The Reference Nutrient Intake is in the order of 100 mg (it varies between countries), which is more than sufficient to prevent overt vitamin C deficiency. The US FNB of the Institute of Medicine, having thoroughly considered the wide literature on vitamin C and many kinds of speculated harms, stated that the safe range for daily supplementation is up to 2,000 mg/day [i].
[i] https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
How much vitamin C should I take for a cold or when infected?
When you get the first signs of a cold, or any infection, load up with 2 to 5,000mg (2-5g) immediately, then take between 500mg and 1,000mg (1gram) and hour, up to your ‘bowel tolerance’ until symptoms disappear. Based on clinical trials, the higher the dose, and the longer you take it, the greater is the reduction in both duration and severity of symptoms. With at least 6g in the first day, studies report between a 20% to 85% shorter infection.
How much vitamin C should I give my child?
As a rule of thumb give the same as an adult but divided by bodyweight. So, if your child is half your weight give half the adult amount. Or, when infected, up to bowel tolerance level.
Can’t you get all the vitamin C you need from a well balanced diet?
You can get enough to prevent scurvy and overt vitamin C deficiency but not enough to most effectively shorten the duration and lessen the severity of a cold which requires gram doses. An orange is roughly 50 mg so twenty oranges provides 1 gram. Older people, especially those with co-morbidities which may require higher intakes (e.g. 400 mg a day) to maintain normal blood levels. An intake of 500 mg a day, roughly ten oranges, equates to lowest risk for cardiovascular disease. Pauling calculated that the recommended daily intake should be 2,000 mg while most RDAs/RNIs are between 70 and 200 mg.
The best food sources of vitamin C, listed here in the order of those with the most vitamin C per calorie, with the figures in brackets being how much you get in 100 g (3.5 oz) , which is roughly a serving are Peppers (100 mg), watercress (60 mg), cabbage (60 mg), broccoli (110 mg), cauliflower (60 mg), strawberries (60 mg), lemons (50 mg), kiwi fruit (55 mg), peas (25 mg), melons (25 mg), oranges (50 mg), grapefruit (40 mg), limes (29 mg), tomatoes (60 mg).
Don’t you just excrete anything above 200 mg?
It is true that, when not infected, you absorb increasingly less vitamin C above about 200 mg. However, blood levels do continue to rise, albeit less sharply, up to several grams if spaced out during the day. Roughly 80 to 90% of the first 200 mg is absorbed, compared to 50% of a 2 g dose, 26% of a 6 g dose and 16% of a 12 g dose.
Supplementing up to at least 2.5 g for most people on most days more than doubles blood plasma levels compared to ‘RDA’ levels, even though the excess is finally excreted. If you supplement 2,000 mg a day spread out through the day you can expect your circulating plasma level to be three times higher than someone who just gets the RDA level. This is a big advantage because it is much harder for viruses and certain pathogenic bacteria, to survive at these concentrations.
Animals that make vitamin C make enough to also excrete some in the urine which has protective effects on the genito-urinary system. It is normal to excrete vitamin C. Also, vitamin C (ascorbic acid) that is ‘spent’ is excreted in the form of dehydroascrobic acid (DHA). Studies measuring vitamin C excretion often fail to take this into account which gives a measure of how much vitamin C has been used. Having no vitamin C in the urine is a sign of deficiency or kidney dysfunction.
Here’s how it works. At low daily doses, below 100mg, the blood plasma levels are roughly less than 40 µmol/l. Below this level vitamin C is reabsorbed by the kidney to prevent scurvy and then oxidised (during it’s antioxidant and enzyme cofactor functions) to dehydroascorbate, then reduced back to ascorbate (also to prevent scurvy). The body is therefore using energy to retain a basic vitamin C level and recycling it to prevent you from becoming sick. That’s why you don’t get scurvy immediately. The body recycles much of it as well as it can.
Each molecule of ascorbic acid can deliver two antioxidant electrons to the body, disarming harmful oxidants, and creating dehydroascorbate. This can then be converted back into ascorbic acid to do it all again. But that takes energy. Finally ascorbate + dehydroascorbate is excreted in the urine. The difference between the ascorbate absorbed and that excreted (not as dehydroascorbate) is one way to get a measure of the antioxidant potential added to the body.
The excretion of high doses is thus part of the mechanism of benefit. The body does not need to use energy trying to generate antioxidant electrons as it gets them for free from the high dose supplement. Another advantage of higher dose vitamin C is that it is excreted in the urine. This protects the bladder and urinary tract.
How is covid different to a cold or flu?
For most it is not. For a small minority, usually after two weeks of infection when breathing is becoming harder, the immune system can over-react against the quantity of dead virus particles in the lungs and bloodstream triggering what is being called a ‘cytokine storm’ or hyper-inflammatory reaction. This is like a fire out of control and must be brought under control quickly to avoid death.
This requires both steroid drugs, mimicking the body’s own adrenal cortisol hormone, and vitamin C, also stored and released from the adrenal glands[i] under conditions of physiological stress. When vitamin C is depleted exogenous intravenous vitamin C, plus steroids and other medications are called for.[2]
[i] Patak P, Willenberg HS, Bornstein SR. Vitamin C is an important cofactor for both adrenal cortex and adrenal medulla. Endocr Res. 2004 Nov;30(4):871-5. doi: 10.1081/erc-200044126. PMID: 15666839
[ii]Marik P, Kory P, Varon J, Iglesias J, Meduri GU.. MATH+ protocol for the treatment of SARS-CoV-2 infection: the scientific rationale. Expert Review of Anti-infective Therapy ,18 Aug 2020, published online DOI:10.1080/14787210.2020.1808462; https://covid19criticalcare.com/math-hospital-treatment/scientific-review-of-covid-19-and-math-plus/?fbclid=IwAR1om-OIvUO9UHK2FJ_DldebLx_r3DgZesquPaS11FejHQFQvbgvr6Psw0Y#1596274217294-29a4f4e2-63ce
What should people hospitalised with serious COVID-19 be given?
There is a compelling case to give high dose oral vitamin C to hospitalised patients, or start them on an intravenous drip. In critical COVID, when a person needs assisted breathing and feeding, intravenous vitamin C is preferable. Amounts given vary from 1 g to 12 g every 12 hours. Some emergency medicine experts report the best effect with 3 g every 6 hours.
Oral doses are the same for those with infection. For example, a loading dose of 3 g followed by 1 g an hour, or 2 g every two hours. The most effective dose has yet to be determined. This dose, however, is not associated with any adverse effects except loose bowels if taken orally, in which case the dose can be lowered to the ‘bowel tolerance’ level.
Does vitamin C help ‘long’ COVID-19 or post COVID recovery?
It is too early to have any studies about this but there is a rationale for vitamin C. If a person has had a few weeks with depleted vitamin C levels, plus a raging viral and/or inflammatory attack causing high levels of oxidants and inflammation it is entirely probable that lungs, muscles, the heart and the brain can get damaged or inflamed. Vitamin C is a required co-factor in making collagen, the cellular glue that holds all cells and membranes together, including the ‘inner skin’ of the lungs and digestive system, as well as connective tissue in the ligaments, tendons, muscles and joints.
What if I’ve got G6PD deficiency or haemochromatosis?
Those with glucose-6-phosphate deficiency (G6PD) have problems metabolising large amounts of vitamin C. Those with the genetic disorders haemochromatosis or thalassaemia are unable to detoxify iron and, due to enhanced iron absorption with vitamin C, need to be careful with higher intake of vitamin C. G6PD deficiency is not considered an exclusion criterion in the use of up to 6 g/day orally or intravenously for a short period of time[i]. The FLCCC report that 3 g every 6 hours appears to be safe in patients with G6PD. It may be wise for those with haemochromatosis or thalassaemia to avoid high dose vitamin C taken with iron-rich foods or supplements and short-term high dose vitamin C to be medically monitored.[ii] The danger with G6PD deficiency is hemolysis which lowers red blood cell count, and can result in oxidative stress within the red blood cells.[iii]
[i] Marik PE. Is intravenous Vitamin C contraindicated in patients with G6PD deficiency? Crit Care. 2019;23:109. DOI:10.1186/s13054-019-2397-6
[ii] Gerster H ‘High-dose vitamin C: a risk for persons with high iron stores?‘ International Journal of Vitamin Nutrition Research 1999 Mar;69(2):67-82. DOI: 10.1024/0300-9831.69.2.67.
Doesn’t high dose vitamin C give you kidney stones?
There used to be a concern that taking too much would raise oxalic acid, thus stressing the kidneys and causing kidney stones. Early experiments had reported raised oxalic acid levels, but this was discovered to be due to a faulty study design. The apparently higher levels of oxalic acid in the urine that have been previously reported arise from the fact that ascorbic acid, which is excreted in the urine, undergoes a chemical conversion to oxalic acid while it is in a test-tube prior to analysis.
This was proven several years ago by research at the Kidney Stone Research Laboratory of the University of Cape Town where they conducted a controlled trial in which ten volunteer subjects were required to ingest 4 g of vitamin C per day for five days. Urine (24h) was collected before, during and after the ingestion period. Unlike the earlier studies they simply put a preservative in the urine collection bottles to prevent this conversion in the test tube. Previous studies failed to take this precaution and hence reported erroneously high oxalic acid levels in the urine.
These were rigorously analysed for a host of independent physicochemical risk factors, all of which are regarded as powerful indicators of the risk of kidney stone formation. The results showed that these risk factors were not significantly altered.
They concluded that ingestion of large doses of vitamin C does not increase the risk of forming kidney stones. The results of this study were published in 1998.[i]
I asked one of the authors, Professor Allen Rodgers from the University of Cape Town, one of the world’s leading experts on kidney stones, if vitamin C could cause kidney stones and he said “The answer is simply no.” On the basis of this research the official position of the Food Standards Agency in the UK is that vitamin C doesn’t increase kidney stone risk.
Long-term studies of people taking vitamin C supplements and the incidence of kidney stones are rather ambiguous. A prospective cohort study of 85,557 women with no history of kidney stones, and 1078 with incidence of kidney stones over 14 years reported that vitamin C was not associated with risk.[ii] A systematic review of studies giving vitamin C found a correlation between ascorbic acid supplementation and the incidence of kidney stones in men, but not women. [iii]
For the vast majority short-term high dose vitamin C, taken to combat a cold or flu is extremely unlikely to be of any concern.
[i] B Auer et al, ‘The Effect of Ascorbic Acid Ingestion on the Biochemical and Physicochemical Risk Factors Associated with Calcium Oxalate Kidney Stone Formation.’ Clinical Chemistry and Laboratory Medicine, (1998), 36(3):143-7.
[https://www.ncbi.nlm.nih.gov/pubmed/9589801]
[ii] Curhan GC, Willett WC, Speizer FE, Stampfer MJ. Intake of vitamins B6 and C and the risk of kidney stones in women. J Am Soc Nephrol. 1999 Apr;10(4):840-5. PMID: 10203369.
[iii] K Jiang, ‘Ascorbic Acid Supplements and Kidney Stones Incidence Among Men and Women: A systematic review and meta-analysis.’ Urology Journal, (2019), 16(2):115-20. [http://www.urologyjournal.org/index.php/uj/article/view/4275] DOI: 10.22037/uj.v0i0.4275
Doesn’t too much vitamin C give you diarrhoea?
Yes, high dose vitamin C can give you diarrhoea or, more accurately, loose bowels since it is lighter, bulkier stool matter that is eliminated, not fluid as in diarrhoea. This is much like soluble fibre, which helps retain more water in faecal matter. Our body passes eight litres of water into the digestive tract every day. If a bit more leaves via the bowel it is not a big deal but, just in case, make sure you’re drinking at least eight glasses of water a day. In other words, you are not going to become dehydrated due to vitamin C. Exactly why this occurs is not completely clear but it is probably due to increased water retention or osmotic pressure, hence the loose bowels. This is how magnesium sulphate (Epsom salts) works as a laxative. Other symptoms include flatulence and mild discomfort. It goes away with a reduced dose. People vary in how much vitamin C they can tolerate in this regard. Looser bowels, or diarrhoea, rarely occurs below 3 g/day and tolerance is increased considerably when fighting a viral infection.[i] The European Food Safety Authority state that the lowest observable adverse effect level is 3-4 g/day (in relation to gastrointestinal effects).[ii] Diarrhoea has not been reported as a complication in hospital-based oral treatment and does not occur, in any event, with intravenous vitamin C administration.
Many experienced practitioners using high dose vitamin C recommend going up to ‘bowel tolerance’ levels – in other words, find the level that makes you too loose, then lower the dose until this stops. Different people have different sensitivities to vitamin C. Your tolerance will be much higher when fighting an infection.
[ii] http://www.efsa.europa.eu/sites/default/files/efsa_rep/blobserver_assets/ndatolerableuil.pdf
I get a mild stomach upset with high dose vitamin C. Why is that?
The primary route for vitamin C absorption is through the early part of the small intestine, which requires relatively high acid levels. If you under produce stomach acid, or are on antacid medication, it is possible that you’ll get less immediate absorption. Try taking your vitamin C at the very start of a protein containing meal, when your body is stimulated to produce stomach acid, or/and with some citrus juice (citric acid) or diluteed cider vinegar (acetic acid) eg a spoonful in water. This might help. Some people tolerate the alkaline form of mineral ascorbates better.
Does vitamin C interfere with any medication?
There are no significant drug interactions with vitamin C, however, it does detoxify some drugs and therefore could make some drugs, such as amphetamines a bit less effective. There’s a list on this website[i] [https://www.drugs.com/drug-interactions/ascorbic-acid,vitamin-c-index.html] of drugs that have a moderate risk of interaction. Check if any you are taking are on this list. There are none that have a major interaction. It also enhances thyroid function (and can enhance thyroid drug uptake) [ii] and has considerable cardiovascular benefits[iii]. Consequently, medication for these conditions may need to be reviewed with long-term vitamin C use. The side-effects of long-term vitamin C are overwhelmingly beneficial. If in doubt speak to your doctor.
[i] See https://www.drugs.com/drug-interactions/ascorbic-acid,vitamin-c-index.html
[ii] W Jubiz and M Ramirez, ‘Effect of vitamin C on the absorption of levothyroxine in patients with hypothyroidism and gastritis.’ The Journal of Clinical Endocrinology & Metabolism, (2014), 99(6):E1031-4. [https://academic.oup.com/jcem/article/99/6/E1031/2537305]
[iii] See https://lpi.oregonstate.edu/mic/vitamins/vitamin-C#cardiovascular-disease-prevention
Wasn’t vitamin C proven to not reduce the incidence of colds?
In 2013, Professor Harri Hemilä, together with Elizabeth Chalker, did the most comprehensive review of all vitamin C studies[i], called a Cochrane systematic review, with the aim being “To find out whether vitamin C reduces the incidence, the duration or severity of the common cold when used either as a continuous regular supplementation every day or as a therapy at the onset of cold symptoms.” They excluded any studies giving less than 200 mg a day. They found that for the most part vitamin C didn’t reduce the number of colds but did reduce the severity and duration of colds, in those experiencing enhanced physical stress.
In 2017, Harri Hemilä revisited the studies, paying more attention to the question of dose. He reported that “Two controlled trials found a statistically significant dose – response, for the duration of common cold symptoms, with up to 6-8 g per day of vitamin C. Thus, the negative findings of some therapeutic common cold studies might be explained by the low doses of 3-4 g/day of vitamin C.” What he found was that the more vitamin C that was given on the first day of a viral infection, the better were the results.
He also found that while there were not a lesser number of colds if you combined all studies “Vitamin C has prevented colds in British men”.[ii] Four trials found that vitamin C decreased the incidence of colds by 30%, and in another set of four trials, the proportion of men who had recurrent common cold infections during the study decreased by a mean of 46%. That’s almost a halving in number of colds. Vitamin C also halved the incidence of colds in five randomised controlled trials during which the participants were under heavy short-term physical activity. A more recent small study in the US reported a 45% decrease in the number of colds through supplementation in those with low vitamin C levels.[iii] Then, two other studies reported that 16% and 17% more of those children taking vitamin C versus placebo didn’t succumb to infection.[iv] If you put this the other way around, one in six children taking vitamin C didn’t get a cold.
Hemilä also shows that, if the dose is higher (4 g to 8 g per day) the duration is shorter. In two studies giving placebo, 3-4 g versus 6-8 g on the first day, the duration of colds was 10% shorter with 3-4 g and 20% shorter with 6-8 g on the first day. In those taking 8 g on the first day, 46% had symptoms that only lasted for one day.[v]
What happens if you take it for longer? In a five day study only giving 1.5 g on the first day and to 1 g of vitamin C thereafter there was a 25% reduction in duration.
What happens if you give more, and take it for longer? In 1999 a study involving 463 students age 18 to 32, were given either 1 g of vitamin C every hour for the first six hours of a cold or flu, then 3 g a day thereafter, or pain relievers and decongestants.[vi] “Flu and cold symptoms in the test group decreased 85% compared with the control group.” Those taking vitamin C halved the duration of the cold, from 7 days to 3.5 days, compared to those taking cold medication. (This study tested the groups over different winters so they weren’t necessarily exposed to the same cold viruses.)
[i] H Hemilä and E Chalker, ‘Vitamin C for preventing and treating the common cold.’ Cochrane Database of Systematic Reviews, (2013). [https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD000980.pub4/abstract]
[ii] H Hemilä, ‘Vitamin C intake and susceptibility to the common cold.’ British Journal of Nutrition, (1997), 77:59-72. [https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0007114500002889]; see also C Bates et al, ‘Vitamin C intake and susceptibility to the common cold: Invited comments and Reply.’ British Journal of Nutrition, (1997), 78:857-66; see also H Hemilä, ‘Vitamin C and common cold incidence: A review of studies with subjects under heavy physical stress.’, International Journal for Sports Medicine, (1996), 17:379-83. [https://www.thieme-connect.com/products/ejournals/abstract/10.1055/s-2007-972864]
[iii] C Johnston, ‘Vitamin C supplementation slightly improves physical activity levels and reduces cold incidence in men with marginal vitamin C status: a randomized controlled trial.’ Nutrients, (2014), 6(7):2572-83. [https://www.mdpi.com/2072-6643/6/7/2572]
[iv] J Coulehan et al, ‘Vitamin C prophylaxis in a boarding school.’ New England Journal of Medicine, (1974), 290(1):6-10. [https://www.nejm.org/doi/full/10.1056/NEJM197401032900102]; see also M Van Straten and P Josling, ‘Preventing the common cold with a vitamin C supplement: a double-blind, placebo-controlled survey.’ Advances in Therapy, (2002), 19(3):151-9. [https://link.springer.com/article/10.1007/BF02850271]
[v] H Hemilä, ‘Vitamin C and Infections.’, Nutrients, (2017), 9(4):339. [https://www.mdpi.com/2072-6643/9/4/339]
[vi] H Gorton and K Jarvis, ‘The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections.’ Journal of Manipulative and Physiological Therapeutics, (1999), 22(8):530-3.[https://www.ncbi.nlm.nih.gov/pubmed/10543583]
What does vitamin C actually do?
Vitamin C is a reducing agent (ie electron donor) with anti-viral properties. Vitamin C increases production and function of our ‘immune cells’ – B-cells, T-cells and macrophages or phagocytes. These are all white blood cells which have ten times more vitamin C in them than red blood cells. B-cells make more antibodies to target the invading virus with increased vitamin C. T-cells are our primary defence against viruses. Macrophages or phagocytes use vitamin C to both capture and kill viruses. Vitamin C increases the production, and improves the function of all of these critical immune cells.[i]
Vitamin C protects immune cells from oxidative damage. These immune cells load up on vitamin C which protects them from oxidative damage.[ii]
Vitamin C has been shown to increase interferon production[iii] and white blood cells release cytokines, including interferons, which have antiviral activity inhibiting viral replication.
Vitamin C is a neuraminidase inhibitor, which is a spike viruses use to get inside cells, thus slowing down viral infection.
Vitamin C is also anti-inflammatory, bacteriostatic or bactericidal.
There’s a good review of vitamin C’s immune function in this linked review. [iv]
[i] R Jariwalla and S Harakeh, ‘Antiviral and immunomodulatory activities of ascorbic acid.’ In: Harris JR, ed. Subcellular Biochemistry, (1999), Vol. 25. Ascorbic Acid: Biochemistry and Biomedical Cell Biology. New York: Plenum Press; 1996:215-231; see also B Kennes et al, ‘Effect of vitamin C supplements on cell-mediated immunity in old people.’ Gerontology, (1983), 29(5):305-10 [https://www.karger.com/Article/Abstract/213131]. See alsoR Panush et al, ‘Modulation of certain immunologic responses by vitamin C. III. Potentiation of in vitro and in vivo lymphocyte responses.’ International Journal for Vitamin and Nutrient Research Supplement, (1982), 23:35-47. [https://miami.pure.elsevier.com/en/publications/modulation-of-certain-immunologic-responses-by-vitamin-c-iii-pote];see also W Prinz et al, ‘The effect of ascorbic acid supplementation on some parameters of the human immunological defence system.’ International Journal for Vitamin and Nutrient Research, (1977), 47(3):248-57. [https://europepmc.org/article/med/914459]; see also S Vallance, ‘Relationships between ascorbic acid and serum proteins of the immune system.’ British Medical Journal, (1977), 2(6084):437-8. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1631223/]; see alsoR Anderson et al, ‘The effects of increasing weekly doses of ascorbate on certain cellular and humoral immune functions in normal volunteers.’ American Journal of Clinical Nutrition, (1980), 33(1):71-6. [https://academic.oup.com/ajcn/article-abstract/33/1/71/4692324 ]; see also R Levy et al, ‘Vitamin C for the treatment of recurrent furunculosis in patients with impaired neutrophil functions.’ The Journal of Infection Diseases, (1996), 173(6):1502-5. [https://academic.oup.com/jid/article/173/6/1502/1010162]
[ii] P Bergsten et al, ‘Millimolar concentrations of ascorbic acid in purified human mononuclear leukocytes. Depletion and reaccumulation.’ The Journal of Biological Chemistry, (1990), 265(5):2584-7. [https://www.jbc.org/content/265/5/2584.full.pdf]; see also R Evans et al, ‘The distribution of ascorbic acid between various cellular components of blood, in normal individuals, and its relation to the plasma concentration.’ British Journal of Nutrition, (1982), 47(3):473-82. [https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/distribution-of-ascorbic-acid-between-various-cellular-components-of-blood-in-normal-individuals-and-its-relation-to-the-plasma-concentration/ADA982B6635876F2E0A00E7F88040DC8]; see also R Jariwalla and S Harakeh, ‘Mechanisms underlying the action of vitamin C in viral and immunodeficiency disease.’ In: Packer L, Fuchs J, eds. Vitamin C in Health and Disease. New York: Macel Dekker, Inc.; (1997):309-22.
[iii] H Dahl and M Degre, ‘The effect of ascorbic acid on production of human interferon and the antiviral activity in vitro.’ Acta Pathologica Microbiologica Scandinavica Section B Microbiology, (1976), 84B(5):280-4. [https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1699-0463.1976.tb01938.x]
[iv] A Carr and S Maggini, ‘Vitamin C and immune function.’ Nutrients, (2017), 9(11):1211. [https://www.mdpi.com/2072-6643/9/11/1211]
How do you know if someone is vitamin C deficient?
The symptoms of a lack of vitamin C result in frequent colds, lack of energy, frequent infections, bleeding or tender gums, easy bruising, nose bleeds, slow wound healing and red pimples on skin.
Vitamin C is measured in the plasma or serum (the clear fraction of the blood). Most government recommended intakes are based on what is needed to achieve a plasma level of 40-50µmol/l. A low level (hypovitaminosis) is defined as a serum level below 23 µmol/l while overt deficiency, as seen in people with scurvy, is below 11µmol/l. The UK’s National Diet and Nutrition Survey, based on a cross section of the UK population, reports that 4% of 65+ year olds have vitamin C levels ≤11nmol. An optimal level is probably 60 to 100µmol/l.
Although 100 mg a day of vitamin C can maintain a normal plasma level in a healthy person, much higher doses (2-3 g/day) are needed to keep plasma vitamin C levels of critically ill patients within the normal range.[[i]] [[ii]]
These measurements relate to blood levels. Since vitamin C is excreted in the urine deficiency can also be indicated by a lack of vitamin C in the urine, which can be crudely tested with urine vitamin C strips.
[i] de Grooth HJ, Manubulu-Choo WP, Zandvliet AS, Spoelstra-de Man AM, Girbes AR,Swart EL, Oudemans-van Straaten HM. Vitamin C pharmacokinetics in critically ill patients: a randomized trial of four iv regimens. Chest 2018;153:1368–1377; DOI:10.1016/j.chest.2018.02.025
[ii] Hume, R.;Weyers, E. Scottish Medical Journal. 1973, 18, 3–7. Changes in leucocyte ascorbic acid during the common cold. DOI: 10.1177/003693307301800102
Does vitamin C work against all viruses?
Vitamin C is strongly antiviral against every virus tested so far. There are many other viral diseases that respond to vitamin C. These include chicken pox, viral hepatitis, herpes, HIV, measles, mumps, viral pneumonia, polio, and rabies. The supporting research is described in Dr Thomas Levy’s book Curing the Incurable: Vitamin C, Infectious Diseases, and Toxins, citing 1,200 referenced studies and available for free as a pdf download.[i]
[i] Download ‘Curing the Incurable’ by Dr Thomas levy from https://epdf.pub/queue/vitamin-c-infectious-diseases-and-toxins-curing-the-incurable.html
How much vitamin C do animals make?
Almost all animals make vitamin C. Humans and other primates have lost that ability due to random genetic mutations knocking out the synthesising machinery. In the wild, gorillas eat 4.5 g of vitamin C a day on average.[i] Monkeys need in the region of a gram a day to be healthy. One study found that the average 7.5 kg monkey (a tenth of our weight) takes in 600 mg per day of vitamin C.[ii]
Animals that make vitamin C, make a lot. A goat makes 200 mg/kg each day. So, if they were my bodyweight they’d be making 15 g a day. Rats make 70 mg/kg, the equivalent of 5.25 g a day. If stressed, this goes up to the bodyweight equivalent of 16 g a day. Dogs and cats make less – the equivalent of 2 g to 3 g a day.[iii]
[i] K. Milton, ‘Micronutrient intake of wild primates: are humans different?’ Comparative Biochemistry and Physiology Part A, (2003),136: 47-59 [https://nature.berkeley.edu/miltonlab/pdfs/kmilton_micronutrient.pdf]
[ii] See https://www.berkeley.edu/news/media/releases/99legacy/5-18-1999.html
[iii] A Conney A et al ‘Metabolic interactions between l-ascorbic acid and drugs’ Ann NY Academy Sci, 92;115-127; see also L Pauling ‘Evolution and the need for ascorbic acid’ Proceedings of the National Academy of Sciences of the USA (1970), 67:1643-1648
Which animals don't make vitamin C?
There are very few animals that don’t make vitamin C. These are:
Primates – which includes tarsiers, monkeys and apes, including humans
Guinea pig and capybara – jungle dwelling rodents
Fruit-eating bats – many, but not all, species of bats don’t make vitamin C
Red vented bulbul bird – a jungle dwelling, fruit eating bird
The Amazonian ornamental ‘oscar’ fish and teleost fish
Isn’t ascorbic acid synthetic? What’s the best form of vitamin C?
Vitamin C comes in two forms – ascorbic acid and ascorbates, sometimes called ‘buffered’ vitamin C. Ascorbic acid is acidic and ascorbate is alkaline. Acidity or alkalinity is measured as pH. A pH of 7 is neutral, with anything less being acidic and anything more being alkaline. Some people claim, or have found, that they tolerate ascorbates better than ascorbic acid. There is no real evidence for this so it is down to your own experience.
Many people mistakenly think anything ‘acidic’ is bad and that ascorbic acid is ‘synthetic’. Vitamin C is ascorbic acid and all plants make ascorbic acid from fructose while animals synthesize it from glucose. It is made in a laboratory in a similar way, synthesizing it from glucose.
While it is true that a continuously increased acid level in the blood is associated with many disease states, the body controls the pH of blood very closely.
However, the body also protects itself by being acidic. The skin is pH 5.5. The stomach is pH 4 to 6. This acid level helps kill dangerous microbes. Ascorbic acid is pH 2 so, if taken with food, this might slightly lower the stomach’s pH level, however, it does naturally drop to a pH of 2 when digesting protein. An increased stomach acid level may assist the absorption of vitamin C.
Consequently, ascorbate forms of vitamin C, which average pH 7 to 8, in high dose would be better taken away from meals so as not to dilute stomach acid levels, essential for optimal digestion. The increased alkalinity is due to the ‘alkaline’ minerals attached to the ascorbic acid – usually calcium, sodium, potassium or magnesium.
Mineral ascorbates is a way to deliver an essential mineral together with vitamin C, wasting less space in a supplement. The problem with a pure mineral ascorbate, at high doses, is that the digestive system has to release stomach acid to get it below pH 7 for absorption. With repeated doses it gets harder and harder. That’s why, when high amounts are needed to fight an infection ascorbic acid tends to work better than ascorbates.
However, something to be aware of if you are taking high daily doses of ascorbates is how much sodium, potassium, calcium, magnesium, manganese or zinc you’re getting. These minerals have other benefits and potential downsides at high doses. Sodium ascorbate, in high doses, adds to the sodium (salt) load and is not good if you have hypertension. However, you cannot inject ascorbic acid into the bloodstream, it is too acidic. So, most intravenous vitamin C is sodium ascorbate.
While zinc and magnesium are among the most commonly deficient minerals and have positive effects in boosting immunity, if you are taking very large daily amounts of these ascorbates do check you’re not exceeding 50mg of zinc, 20mg of manganese or 500mg of magnesium for more than a few days.
Potassium is both a very abundant mineral in our diets (a cup of beans will give you 1,000mg while an avocado can provide 700mg) and may also have anti-cancer benefits.
Liposomal vitamin C is vitamin C in a liposomal capsule designed to aid delivery into the bloodstream. In one study volunteers were given either 4 g of ascorbic acid or 4 g of liposomal ascorbic acid. Plasma vitamin C levels were then measured over a four hour period, on the hour.[i] By looking at the average over the 4 hours, oral delivery of vitamin C encapsulated in liposomes scored 10.3 mg/dLh versus 7.6 mg/dLh which equates to 26% more being absorbed. If you want to get to high blood levels, and have hit your ‘bowel tolerance’ level, or have gastric upset, then taking liposomal ascorbic acid may be advisable.
[i] J Davis et al, ‘Liposomal-encapsulated Ascorbic Acid: Influence on Vitamin C Bioavailability and Capacity to Protect Against Ischemia–Reperfusion Injury.’ Nutrition and Metabolic Insights, (2016), 9:25-30. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4915787/]
Can’t you only get to really high blood levels with intravenous vitamin C? Is IV vitamin C safe?
One of the potential advantages of intravenous vitamin C, either given as sodium ascorbate, or pure ascorbic acid added into a saline drip to produce the right pH, is that you can get to higher and sustained levels of vitamin C in the blood, which is profoundly antiviral. This occurs with blood levels above 0.25mM.
Some erroneously say that this can only be achieved with intravenous vitamin C. Steve Hickey, author of Ascorbate – the Science of Vitamin C, states “We’ve measured 0.25mM from a single 5 gram dose of vitamin C and recorded 0.42mM with a 36 gram dose of liposomal vitamin C. It looks like you could sustain a level of 0.4, and possibly 0.5mM in the plasma if you keep taking in vitamin C at a high level.”
In critical COVID, when a person needs assisted breathing and feeding, intravenous vitamin C is preferable. Amounts given vary from 1 g to 12 g every 12 hours. Some emergency medicine experts report the best effect with 3 g every 6 hours.
The peak level of vitamin C in the blood for both intravenous and oral vitamin C is around 2 hours so, within 4 hours vitamin C levels drop off. Thus, giving vitamin C at least every six hours is likely to be far more effective than a daily or twice daily dose.
A survey of 9,328 patients given an average intravenous dose of 24 g of vitamin C every 4 days primarily for cancer, infection or fatigue reported 101 had side effects, mostly minor, including lethargy/fatigue in 59 patients, change in mental status in 21 patients and vein irritation/phlebitis in 6 patients.[[i]]
[i] Padayatty SJ, Sun AY, Chen Q, Espey MG, Drisko J, Levine M (2010) Vitamin C: Intravenous Use by Complementary and Alternative Medicine Practitioners and Adverse Effects. PLoS ONE 5(7): e11414. DOI:10.1371/journal.pone.0011414
Which other nutrients help vitamin C to work?
Vitamin C works with many other nutrients, the main ones being vitamin E, glutathione, alpha lipoic acid, anthocyanidins and Co-Enzyme Q10. How these work together is shown in this short animation – antioxidant teamplayers. There are other co-factor nutrients including zinc, which has evidence of efficacy against colds, B vitamins, magnesium, copper, manganese and selenium. No antioxidant works in isolation so having a good intake of these, through diet and supplements helps vitamin C to work better. Vitamin D, which also has evidence of reduced COVID-19 risk, helps promote glutathione levels which, in turn, helps to recycle vitamin C.
What should people in ICU, with decreasing oxygenation, be given?
In critical COVID-19, when a person needs assisted breathing and feeding, intravenous vitamin C is preferable in combination with anti-inflammatory steroid medication as it enhances the anti-inflammatory effect. Amounts given vary from 1 g to 12 g every 12 hours until the inflammation reduces and oxygenation improves. Some emergency medicine experts report the best effect with 3 g every 6 hours.
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