All you need to know about: Vitamin C

Vitamin C (Ascorbic acid)

12-06-2015
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What you can achieve by taking it
Supports your immune system
Vitamin C has a proven effect of supporting the immune system, let it be an illness or excessive stress. And intense and regular workout is also a sort of excessive stress.
Strengthens connective tissues
Beside the anti-inflammatory (and preventive) effect of vitamin C, it also supports and strengthens joints (tendons and ligaments).
Anti-inflammatory effect
Vitamin C reduces both acute and chronic inflammations, as well as inflammations resulting from workout.

%
500 tab. 
 
34%   £ 24.30  
£ 16.05
100 tab. 
 
 
£ 6.27
250 tab. 
 
 
£ 13.58
100 caps 
 
 
£ 7.27

Review

We Hungarians are especially fond of vitamin C, discovered by Hungarian physiologist Albert Szent-Györgyi. It quickly became popular, mostly as a natural remedy for flu and common cold. But for athletes, this supplement can be important for one more reason beside supporting the immune system: this is namely its joint support effect, which has gained publicity lately.

Why it is worth using

Intense workout is good for you, isn’t it? Well... Yes, it is. Still, stress is stress; no matter where it’s coming from. Workout poses significant load on your system. So, even if you are introducing it gradually, allowing your system enough time to adapt, it is still recommended to support your immune system with some vital substances (vitamins, minerals, protein etc.) that will enable your body to prepare for taking this extra load.

And this is when vitamin C comes into the picture. The needs of athletes are higher than the officially (medically) established RDA levels, especially if there are no existing risk factors (like the widespread urban legend about kidney stones). Vitamin C supplementation is essential for ensuring flawless immune functions for athletes, and even for individuals who lead an active lifestyle and work out for recreational purposes.

Further effects

Facilitates muscle recovery
Beside other antioxidants, Vitamin C plays a key role in ensuring faster and more efficient recovery of the micro-traumas in the muscles that occur naturally during workout. All in all, it will shorten your recovery time. Take 1,000 to 2,000 mg of vitamin C before workout to avoid or reduce onset delayed muscle fatigue.
Increases stress tolerance
Stress, either physical or psychological, will compromise the normal, healthy functioning of your system sooner or later. This can be prevented by taking vitamin C on a regular basis.
Diminishes fatigue
Due to its role in the functioning of the thyroid gland, vitamin C can make you feel less tired.
Helps you beat infections
Let it be an external infection from a wound, or an internal infection caused by microorganisms, vitamin C will help you overcome them. It promotes the functioning of virtually all sorts of immune cells.
Detox effect
As a result of various harmful external impacts, the so-called free radicals may accumulate in the body. Free radicals are aggressive molecules that damage the cells of your body through oxidation. Antioxidants bind to these aggressive molecules and help your system get rid of them (detoxification).
Further effects
  • Strengthens capillary vessels
  • Vitamin C is vital for the synthesis of the proteins forming connective tissues (collagen).
  • It supports the red blood cells in the biosynthesis of haemoglobin and promotes the absorption of iron.
  • Helps prevent heart attack
  • Prevents cataracts

How to use it

Quantity: The (official) recommended dietary allowance of vitamin C is only 60 mg. This is such a small amount that there is in fact little chance that it will reach the digestive system at all :( Sadly, for some reason, the pharmaceutical lobby exerts incredible suppression on this simple, cheap and extremely effective substance. Based on several studies in natural medicine, vitamin C can be safely applied in a daily dose of 1,000 to 3,000 mg. And YES, this amount is required to profit from its positive effects. In some illnesses (Crohn's disease, colitis, AIDS, cancer etc.), even a therapeutic dose of 5,000 to 10,000 mg may be necessary.

If you consume less than 10 mg of vitamin C daily, you may get scurvy; and if your daily intake does not exceed 50 mg, you are still exposed to a higher risk of heart diseases, cataracts or premature death.

The recommended daily dose of vitamin C is 40 to 60 mg, and 60 to 100 for smokers. But even the most conservative experts accept that for today’s modern city people, who are exposed to extreme stress because of pollution, the optimal daily vitamin C intake is 200 mg.

Higher doses are required to treat illnesses, or for individuals who are exposed to a load that is HIGHER than average, e.g. athletes, including bodybuilders.

Linus Pauling (the only person to have been awarded two unshared Nobel Prizes), Albert Szent-Györgyi and Leó Szilárd (who also took part in the development of the atomic bomb, and later, he experimented with vitamin C on himself to cure his cancer) all believed that vitamin C powder should be present in every household as a basic item like sugar or flour, and it should be consumed “with a spoon”.

Michael Colgan PhD, one of the world’s most renowned sports physicians even recommends 12 grams of vitamin C for athletes in his books and publications!!!

Sadly, public healthcare pushes us, everyday people to use this excellent and vital nutrient in traces only: in Hungary and the EU, the maximum dose of vitamin C per tablet has been fixed at 60 mg. This would NOT even suffice for a little mouse!!!

Timing: Vitamin C is absorbed quickly, and the excess amount will discharge quickly (in about 2 hours) with urine. For this reason, it is recommended to disperse the daily amount into several smaller amounts throughout the day (taken every 3 or 4 hours).

Synergies

  • There is a synergy between vitamin E and vitamin C: together, both of them enhance the antioxidant effects of the other.
  • The combination of 1,000 mg of vitamin C, 500 mg of vitamin E and 30 mg of beta-carotene raises the level of superoxide dismutase (SOD, one of the most potent antioxidant enzymes of the body) dramatically, ensuring outstanding protection to the body against various harmful and destructive processes.
  • Bioflavonoids (like rosehip) increase the bioavailability of vitamin C in the body. That’s the reason why vitamin C supplements of natural sources are more potent than synthetic preparations.
  • Hesperidine facilitates the antioxidant functions of vitamin C.

Natural sources

Citrus fruits like orange, lemon or grapefruit contain high levels of vitamin C. Many vegetables, like peppers (paprika), broccoli, tomato or sauerkraut are powerful sources, too.

Note: Vitamin C is a highly unstable compound (as an antioxidant, it will react with “anything” in the air), and will break down quickly when heated. Cooking will virtually destroy vitamin C completely. The vitamin C levels in fruit and vegetables that stay out long at the market, can drop dramatically. Tropical fruits are being picked when they are still green and will be ripened artificially. For this reason, their vitamin levels are not as high as many believe. All in all, if you wish to take vitamin C from natural sources, you should go for raw and fresh vegetables and fruit.

Minerals and other variants

In the rapidly expanding market of dietary supplements, it is possible to find vitamin C in many different forms with many claims regarding its efficacy or bioavailability. Bioavailability refers to the degree to which a nutrient (or drug) becomes available to the target tissue after it has been administered. We reviewed the literature for the results of scientific research on the bioavailability of different forms of vitamin C.

Natural vs. synthetic ascorbic acid

Natural and synthetic L-ascorbic acid are chemically identical, and there are no known differences in their biological activity. The possibility that the bioavailability of L-ascorbic acid from natural sources might differ from that of synthetic ascorbic acid was investigated in at least two human studies, and no clinically significant differences were observed.

A study of 12 males (6 smokers and 6 nonsmokers) found the bioavailability of synthetic ascorbic acid (powder administered in water) to be slightly superior to that of orange juice, based on blood levels of ascorbic acid, and not different based on ascorbic acid in leukocytes (white blood cells).

A study in 68 male nonsmokers found that ascorbic acid consumed in cooked broccoli, orange juice, orange slices, and as synthetic ascorbic acid tablets are equally bioavailable, as measured by plasma ascorbic acid levels.

Different forms of ascorbic acid

The gastrointestinal absorption of ascorbic acid occurs through an active transport process, as well as through passive diffusion. At low gastrointestinal concentrations of ascorbic acid active transport predominates, while at high gastrointestinal concentrations active transport becomes saturated, leaving only passive diffusion. In theory, slowing down the rate of stomach emptying (e.g., by taking ascorbic acid with food or taking a slow-release form of ascorbic acid) should increase its absorption. While the bioavailability of ascorbic acid appears equivalent whether it is in the form of powder, chewable tablets, or non-chewable tablets, the bioavailability of ascorbic acid from slow-release preparations is less certain.

A study of three men and one woman found 1 gram of ascorbic acid to be equally well absorbed from solution, tablets, and chewable tablets, but the absorption from a timed-release capsule was 50% lower.

A more recent study examined the plasma levels of ascorbic acid in 59 male smokers supplemented for two months with either 500 mg/day of slow-release ascorbic acid, 500 mg/day of plain ascorbic acid, or a placebo. After two months of supplementation no significant differences in plasma ascorbic acid levels between the slow-release and plain ascorbic acid groups were found.

Mineral ascorbates

Mineral salts of ascorbic acid (mineral ascorbates) are buffered, and therefore, less acidic. Thus, mineral ascorbates are often recommended to people who experience gastrointestinal problems (upset stomach or diarrhea) with plain ascorbic acid. There appears to be little scientific research to support or refute the claim that mineral ascorbates are less irritating to the gastrointestinal tract. When mineral salts of ascorbic acid are taken, both the ascorbic acid and the mineral appear to be well absorbed, so it is important to consider the dose of the mineral accompanying the ascorbic acid when taking large doses of mineral ascorbates. Mineral ascorbates are available in the following forms:

Sodium ascorbate: 1,000 mg of sodium ascorbate generally contains 111 mg of sodium. Individuals following low-sodium diets (e.g., for high blood pressure) are generally advised to keep their total dietary sodium intake to less than 2,500 mg/day. Thus, megadoses of vitamin C in the form of sodium ascorbate could significantly increase sodium intake.

Calcium ascorbate: Calcium ascorbate generally provides 90-110 mg of calcium (890-910 mg of ascorbic acid) per 1,000 mg of calcium ascorbate. Calcium in this form appears to be reasonably well absorbed. The recommended dietary calcium intake for adults is 1,000 to 1,200 mg/day, but it should not exceed 2,500 mg. This should be observed when taking megadoses.

The following mineral ascorbates are more likely to be found in combination with other mineral ascorbates, as well as other minerals. It's a good idea to check the labels of dietary supplements for the ascorbic acid dose as well as the dose of each mineral. Recommended dietary intakes and maximum upper levels of intake (when available) are listed after the individual mineral ascorbates below:

Potassium ascorbate: The minimal requirement for potassium is thought to be between 1.6 and 2.0 g/day. Fruit and vegetables are rich sources of potassium, and a diet rich in fruit and vegetables may provide as much as 8 to 11 g/day. Acute and potentially fatal potassium toxicity (hyperkalemia) is thought to occur at a daily intake of about 18 g/day of potassium in adults. Individuals taking potassium-sparing diuretics and those with renal insufficiency (kidney failure) should avoid significant intake of potassium ascorbate. The purest form of commercially available potassium ascorbate contains 0.175 grams (175 mg) of potassium per gram of ascorbate.

Magnesium ascorbate: The recommended dietary allowance (RDA) for magnesium is 400-420 mg/day for adult men and 310-320 mg/day for adult women. The upper level (UL) of intake for magnesium from supplements should not exceed 350 mg/day.

Zinc ascorbate: The RDA for zinc is 11 mg/day for adult men and 8 mg/day for adult women. The upper level (UL) of zinc intake for adults should not exceed 40 mg/day.

Molybdenum ascorbate: The RDA for molybdenum is 45 micrograms (mcg)/day for adult men and women. The upper level (UL) of molybdenum intake for adults should not exceed 2,000 mcg (2 mg)/day.

Chromium ascorbate: The recommended dietary intake (AI) for chromium is 30-35 mcg/day for adult men and 20-25 mcg/day for adult women. A maximum dosage (UL) of intake has not been determined yet.

Manganese ascorbate: The recommended dietary intake (AI) for manganese is 2.3 mg/day for adult men and 1.8 mg/day for adult women. The upper level (UL) of intake for manganese for adults should not exceed 11 mg/day. Manganese ascorbate is found in some preparations of glucosamine and chondroitin sulfate, and following the recommended dose on the label of such supplements could result in a daily intake exceeding the upper level for manganese.

Other formulations of vitamin C

Ester-C® contains mainly calcium ascorbate, but also contains small amounts of the vitamin C metabolites, dehydroascorbic acid (oxidized ascorbic acid), calcium threonate, and trace levels of xylonate and lyxonate. In their literature, the manufacturers state that the metabolites, especially threonate, increase the bioavailability of the vitamin C in this product, and they indicate that they have performed a study in humans that demonstrates the increased bioavailability of vitamin C in Ester-C®. This study has not been published in a peer-reviewed journal. A small published study of vitamin C bioavailability in eight women and one man found no difference between Ester-C® and commercially available ascorbic acid tablets with respect to the absorption and urinary excretion of vitamin C. Ester-C® should not be confused with ascorbyl palmitate, which is also marketed as "vitamin C ester”.

Vitamin C with bioflavonoids: Bioflavonoids or flavonoids are polyphenolic compounds found in plants. Vitamin C-rich fruit and vegetables, especially citrus fruit, are often rich sources of flavonoids as well. The impact of bioflavonoids on the absorption of vitamin C have been examined in two smaller studies. In one study, a supplement of synthetic ascorbic acid, given in a natural citrus extract containing bioflavonoids, proteins, and carbohydrates (the proportion of the citrus extract to the bioflavonoids was 4:1), was more slowly absorbed and 35% more bioavailable than synthetic ascorbic acid alone. This was stated by monitoring the urinary excretion of ascorbates within a 24-hour period. In another study, the bioavailability of 500 mg of ascorbic acid was examined with bioflavonoids or alone. In this case, the proportion of bioflavonoids to ascorbic acid was 0.05:1, and there was no difference in the absorption and bioavailability of ascorbic acid ingested with or without flavonoids.

Ascorbyl palmitate: Ascorbyl palmitate is a fat-soluble antioxidant used to increase the shelf life of vegetable oils and potato chips. It is an amphipathic molecule, meaning one end is water-soluble and the other end is fat-soluble. This dual solubility allows it to be incorporated into cell membranes. When incorporated into the cell membranes of human red blood cells, ascorbyl palmitate has been found to protect them from oxidative damage and to protect alpha-tocopherol (a fat-soluble antioxidant) from oxidation by free radicals. However, the protective effects of ascorbyl palmitate on cell membranes have only been demonstrated in the test tube. Taking ascorbyl palmitate orally probably doesn't result in any significant incorporation into cell membranes because most of it appears to be hydrolyzed (broken apart into palmitate and ascorbic acid) in the human digestive tract before it is absorbed. The ascorbic acid released by the hydrolysis of ascorbyl palmitate appears to be as bioavailable as ascorbic acid alone. The presence of ascorbyl palmitate in oral supplements contributes to the ascorbic acid content of the supplement and probably helps protect fat-soluble antioxidants in the supplement. The roles of vitamin C in promoting collagen synthesis and as an antioxidant have generated interest in its use on the skin. Ascorbyl palmitate is frequently used in topical preparations because it is more stable than some aqueous (water-soluble) forms of vitamin C.

D-Isoascorbic acid (Erythorbic acid): Erythorbic acid is an isomer of ascorbic acid. Isomers are compounds that have the same kinds and numbers of atoms, but different molecular arrangements. The difference in molecular arrangement among isomers may result in different chemical properties. Erythorbic acid is used in the US as an antioxidant food additive and is generally recognized as safe. Unlike ascorbic acid, erythorbic acid does not appear to exert vitamin C activity, for example, it did not prevent scurvy in guinea pigs (one of the few animal species other than humans that does not synthesize ascorbic acid). However, guinea pig studies also indicated that increased erythorbic acid intake reduced the bioavailability of ascorbic acid by up to 50%. In contrast, a series of studies in young women found that up to 1,000 mg/day of erythorbic acid for as long as 40 days was rapidly cleared from the body and had little effect on the bioavailability of ascorbic acid, indicating that erythorbic acid does not diminish the bioavailability of ascorbic acid in humans at nutritionally relevant levels of intake (about 200 mg in the USA).

Ascorbic acid and tooth enamel

Although you can read a lot about the harmful effect of ascorbic acid on tooth enamel because of its acidic pH, there is little scientific evidence for that. In one of the few related studies, each subject was given a 500mg chewable tablet to dissolve them in their mouths. This made the environment in their mouths acidic enough for a sufficient period of time, to harm tooth enamel. But in the case of 250 or 60mg tablets, neither the pH value nor the duration was strong enough to exert any harmful effect. However, it was not examined in this study how the chewable tablets affected the pH value of saliva. Although some tablets are buffered with sodium, the amount is usually not enough to outweigh tooth enamel erosion resulting from acidic pH. And since chewable tablets have no advantage over capsules or regular tablets, based on the above study, scientists recommend any of the latter two alternatives.

Possible side effects

Safety: Gastrointestinal problems (upset stomach or diarrhea) may occur if you take more than 5,000 mg of vitamin C at a time. For pregnant women, it is not recommended to take more than 5,000 mg of vitamin C daily.

If you take more than 2,000 mg per day on a regular basis, you should keep in mind that vitamin C may hinder the absorption of copper and selenium, so make sure you get enough of these minerals, too.

There is no consensus among physicians on the matter whether taking high doses of vitamin C for an extended period increases the risk of urinary tract stones. There are rumors stating that the formation of kidney stones can be prevented by taking vitamin C; in other views, ascorbic acid has been in fact implicated as a risk factor for people prone to calcium oxalate stones, due to its conversion to oxalate and potential acidifying properties. So, studies are quite controversial on this matter. One thing is for sure: for patients with haemochromatosis (this is a rare hereditary disease characterized by excessive intestinal absorption of dietary iron resulting in a pathological increase in total body iron stores) should not take large doses of vitamin C, because it facilitates the absorption of iron significantly.

A total of 12 calcium oxalate (CaOx) stone formers underwent a study. It was examined how 2,000 mg of ascorbic acid would affect the pH value of urine and the concentration of oxalates, which play a key role in the formation of stones. The study showed no change in the pH value of urine, while the concentration of oxalates (the main risk factors) increased by 20 %; this was evaluated as statistically significant, but not high. Still, if you know that you are a CaOx stone former, you should take this into account. It was not examined in the study whether other factors (amount and mineral content of water etc.) had any influence on the risk factors...
Source: Effect of ascorbic acid consumption on urinary stone risk factors.
Traxer O, Huet B, Poindexter J, Pak CY, Pearle MS.
Department of Urology, The University of Texas Southwestern Medical Center, Dallas, 75390-9110, USA.

Please note: Vitamin C may affect the amount of sugar in the urine or the amount of blood or haemoglobin in the feces. Therefore, before examinations of this kind, always inform your physician that you are taking vitamin C.

Toxicity: Not known.

Block list: Vitamin C is not included in any block list.

The history of vitamin C

In 1742, lemon juice was already used to prevent scurvy (a debilitating disease), which was quite common among sailors during long sea trips. However, vitamin C, the active agent in lemon juice, was not identified until 1928. That was the time when Albert Szent-Györgyi discovered ascorbic acid. He isolated it from the adrenal gland and found that it was identical with vitamin C. He was awarded the Nobel Prize in Physiology or Medicine in 1937 for this discovery. The name ascorbic acid comes from the anti-scurvy effect of vitamin C (the Latin name of scurvy is scorbutus). Today, vitamin C is less popular for its anti-scurvy effect but rather for its role in protecting cells. Being a water-soluble antioxidant, vitamin C protects against the harmful effects of free radicals, especially in a watery environment like, for example, inside of cells.

Q & A on vitamin C

What are the effects of vitamin C?

It would be impossible to list them all, but we are trying to highlight the most important ones: vitamin C supplementation can accelerate the recovery process from common cold (no, it cannot prevent or cure it; but it can ease the symptoms and rev up recovery). Furthermore, it can also diminish allergic symptoms or exercise-induced asthma, running nose, “watery eyes” etc. by reducing endogenic histamine production.
Further studies have proven its support functions that ensure the health of bones, joints, tendons and ligaments. Even though it will not reduce the pain that comes with arthritis, but, complementing an appropriate medical treatment, it may shorten the recovery process. It also eases sunburn symptoms. And these are only a few, most common effects...
However, vitamin C is not a magic potion. You should not expect that it will cure you in itself. However, it is an essential substance, which can be used successfully in multiple ways to facilitate recovery from illnesses or diminish symptoms.

Is there a way to to increase the efficacy of vitamin C?

Actually, it’s vitamin C that can effectively boost other substances. For example, taken with vitamin E and beta carotene, the antioxidant potential of both agents will be boosted. If taken with glucosamine or MSM, it will enhance the anti-inflammatory effects of both; or, if taken with grape seed extract, it will facilitate its positive anti-cancer effect etc.
Studies have shown that the body can utilize vitamin C more efficiently with bioflavonoids. In vitamin C extracts from natural sources, the bioflavonoids are preserved, too.

What is the maximum dose of vitamin C?

The average daily requirement is 1,000 to 2,000 mg. However, most of the physicians and nutritionists disagree with this statement. True: the human body can go without life-threatening deficiency symptoms on 60 mg per day. However, (believe it or not), not only experience, but several physiological studies have proven that this amount is far from enough in cases of significant physical or psychological stress. And, to benefit from the positive effects outlined above in this review, 1,000 to 5,000 mg doses are required per day. Michael Colgan PhD, one of the world’s most renowned sports physicians even recommends 12,0000 mg of vitamin C for athletes.

I read that too much vitamin C may cause kidney stones. Is that true?

No. Kidney stones may consist of calcium oxalate, uric acid or struvite. There is no such a thing as a “vitamin C stone”. One of the main reasons of the formation of kidney stones is glomerulonephritis (a group of diseases that injure the part of the kidney that filters blood) or pyelonephritis (inflammation of the kidney tissue, calyces, and pelvis). And vitamin C actually does not cause any inflammation. On the contrary: it protects you against them! And one of the main reasons of glomerulonephritis is the accumulation of free radicals. And antioxidants, like vitamin C protect your system against free radicals.
However, some studies implied that there may be a correlation between the formation of oxalate or uric acid stones and vitamin C consumption. These studies are strongly doubted by many other physicians, but practically, all studies have critics. Everybody should decide it for themselves. As for ourselves, we believe the incredulous physicians on this matter.

Is it inescapable to take vitamin C supplements? Is it impossible to take vitamin C from natural sources?

No, it’s not impossible. Moreover, The ideal solution would be, if we could provide our bodies all the required amount of vitamin C from fresh and raw fruit and vegetables, together with all the complementary agents that enhance its absorption and bioavailability. But sadly, vitamin C breaks down quickly during cooking or even storage. Oranges might even lose 30 % of their vitamin C content after 3 days of storage! (Especially if stored at a warm place). So, as in many cases, our accelerated modern lifestyle makes it difficult for us to manage this...

Bibliography

Primary:
Earl Mindell: Vitamin Biblia (Vitamin Bible, Hungarian edition)
In: “Vitaminok, gyógynövények, ásványi anyagok” (“Vitamins, herbs and minerals”) – Reader's Digest, Hungarian edition, 2001, Budapest
Bill Phillips: Sports Supplement Rewiev 3rd Issue
PDR for Nutritional Supplements, First Edition, 2001

További referenciák:
Cohen, H.A., et al., "Blocking Effect of Vitamin C in Exercised-Induced Asthma," Arch Pediatr Adolesc Med 151.4 (1997) : 367-70.

Hemila, H., "Does Vitamin C Alleviate the Symptoms of the Common Cold? A Review of Current Evidence," Scand J Infect Dis 26.1 (1994) : 1-6.

Hemila, H., "Vitamin C Supplementation and Common Cold Symptoms: Factors Affecting the Magnitude of the Benefit," Med Hypotheses 52.2 (1999) : 171-8.

Levine, M., et al., "Criteria and Recommendations for Vitamin C Intake," JAMA 281.15 (1999) : 1415-23.

Ness, A.R., et al., "Vitamin C Status and Respiratory Function," Eur J Clin Nutr 50.9 (1996) : 573-9.

Simon, J.A., "Ascorbic Acid and Cholesterol Gallstones," Med Hypotheses 40.2 (1993) : 81-4.

Tauler, P., et al., "Diet Supplementation with Vitamin E, Vitamin C, and Beta-Carotene Cocktail Enhances Basal Neutrophil Antioxidant Enzymes in Athletes," Pflgers Archiv: European Journal Of Physiology 443.5-6 (2002) : 791-7.

Thompson, D., et al., "Prolonged Vitamin C Supplementation and Recovery from Demanding Exercise," Int J Sport Nutr Exerc Metab," 11.4 (2001) :466-81.

Pelletier, O. & Keith, M.O. Bioavailability of synthetic and natural ascorbic acid. Journal of the American Dietetic Association. 1974; 64: 271-275

Mangels, A.R. et al. The bioavailability to humans of ascorbic acid from oranges, orange juice, and cooked broccoli is similar to that of synthetic ascorbic acid. Journal of Nutrition. 1993; volume 123: pages 1054-1061. (PubMed)

Gregory, J.F. Ascorbic acid bioavailability in foods and supplements. Nutrition Reviews. 1993; volume 51: pages 301-309. (PubMed)

Yung, S. et al. Ascorbic acid absorption in humans: a comparison among several dosage forms. Journal of Pharmaceutical Sciences. 1982; volume 71: pages 282-285. (PubMed)

Nyyssonen, K. et al. Effect of supplementation of smoking men with plain or slow release ascorbic acid on lipoprotein oxidation. European Journal of Clinical Nutrition. 1997; volume 51: pages 154-163. (PubMed)

Johnston, C.S. & Luo, B. Comparison of the absorption and excretion of three commercially available sources of vitamin C. Journal of the American Dietetic Association. 1994; volume 94: pages 779-781.

Vinson, J.A. & Bose, P. Comparative bioavailability to humans of ascorbic acid alone or in a citrus extract. American Journal of Clinical Nutrition. 1988; volume 48: pages 501-604. (PubMed)

Cort, W.M. Antioxidant activity of tocopherols, ascorbyl palmitate, and ascorbic acid and their mode of action. Journal of the American Oil Chemists’ Society. 1974; volume 51: pages 321-325.

Ross, D. et al. Ascorbate 6-palmitate protects human erythrocytes from oxidative damage. Free Radical Biology and Medicine. 1999; volume 26: pages 81-89. (PubMed)

DeRitter, E. et al. Physiologic availability of dehydro-L-ascorbic acid and palmitoyl-L-ascorbic acid. Science. 1951; volume 113: pages 628-631.

Austria R. et al. Stability of vitamin C derivatives in solution and in topical formulations. Journal of Pharmacology and Biomedical Analysis. 1997; volume 15: pages 795-801. (PubMed)



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