Vitamin C: benefits, dosage, contraindications
Scientific name(s)
Ascorbic acid
Family or group:
Vitamins
Indications
Scoring methodology
EFSA approval.
Vitamin C deficiency ✪✪✪✪✪
Vitamin C deficiency is common in at-risk populations (single men, elderly people, homeless individuals, those with psychiatric disorders) and underrecognized in the general population. Scurvy is a disease that occurs after three months of total ascorbic acid deficiency, which comes mainly from fresh fruits and vegetables. Clinical manifestations include asthenia, myalgias, arthralgias, a vascular purpura, a hemorrhagic syndrome, and later stomatological manifestations: bleeding gums and tooth loss. Biological signs are nonspecific: anemia, hypocholesterolemia, hypoalbuminemia. Treatment of scurvy consists of administering 1 g of vitamin C divided into several daily doses (intestinal absorption and renal excretion are saturable from an intake of 100 mg), for 15 days orally in most cases, and parenterally in case of malabsorption. The hemorrhagic syndrome disappears within 48 hours and overall improvement occurs within 15 days.
Posologie
Orally
95 mg
15 - days
Immune support ✪✪✪✪✪
Vitamin C appears to increase T-lymphocyte activity, phagocyte function, leukocyte mobility and possibly the production of antibodies and interferon. Furthermore, some researchers believe that vitamin C levels in white blood cells decrease at the onset of a cold and that increasing vitamin C intake may be beneficial. EFSA recognizes that an additional 200 mg of vitamin C on top of the recommended daily intake (100 mg per day) contributes to the normal functioning of the immune system during and after intense physical exercise.
Posologie
By mouth
200 - 3000 mg
Ascorbic acid and the immune response
Vitamin C and SARS coronavirus
Nutritional aspects of ascorbic acid: uses and abuses
T lymphocyte mobility: defects and effects of ascorbic acid, histamine and complexed IgG
Fatigue ✪✪✪✪✪
EFSA recognizes the contribution of vitamin C to the reduction of fatigue. Vitamin C plays a crucial role in various physiological functions such as tyrosine metabolism, the synthesis of several neurotransmitters (norepinephrine, dopamine), and the regulation of iron metabolism. Its role as an antioxidant and its importance in maintaining immunity are well established. A deficiency in vitamin C can lead to fatigue, personality changes, and a decrease in psychomotor performance, often without being diagnosed due to the non-specific nature of the symptoms. Vitamin C is therefore essential to fight fatigue and support many of the body's vital functions.
Posologie
By mouth
100 mg
Daily Vitamin C Consumption and Fatigability
Vitamin C status and perception of effort during exercise in obese adults adhering to a calorie-reduced diet
Intravenous Vitamin C Administration Reduces Fatigue in Office Workers: A Double-Blind Randomized Controlled Trial
Skin health ✪✪✪✪✪
It has been shown that topical application of vitamin C increases collagen production and improves its organization. European health authorities (EFSA, European Food Safety Authority and the European Commission) have concluded that products containing vitamin C (ascorbic acid) may claim to contribute to the normal formation of collagen necessary for the normal functioning of blood vessels, bones, cartilage, skin, teeth and gums.
Posologie
Orally
95 mg
Use of topical ascorbic acid and its effects on photodamaged skin topography
Clinical, biometric and structural evaluation of the long-term effects of a topical treatment with ascorbic acid and madecassoside in photoaged human skin
Topical activity of ascorbic acid: from in vitro optimization to in vivo efficacy
DIETARY SUPPLEMENT: VITAMIN C
Bone health ✪✪✪✪✪
Although the relationship between calcium, vitamin D and bone mineral density is well known, other nutrients, such as vitamin C, are also essential for the development, repair and maintenance of bones. rnrnEuropean health authorities (EFSA, European Food Safety Authority and the European Commission) have concluded that products containing vitamin C (ascorbic acid) may claim to contribute to the normal formation of collagen necessary for the normal functioning of blood vessels, bones, cartilage, skin, teeth and gums. rnrn
Posologie
Oral administration
95 mg
Scientific Opinion on the substantiation of health claims related to vitamin C and protection of DNA, proteins and lipids from oxidative damage (ID 129, 138, 143, 148), antioxidant function of lutein (ID 146), maintenance of vision (ID 141, 142), collagen formation (ID 130, 131, 136, 137, 149), function of the nervous system (ID 133), function of the immune system (ID 134), function of the immune system during and after extreme physical exercise (ID 144), non-haem iron absorption (ID 132, 147), energy-yielding metabolism (ID 135), and relief in case of irritation in the upper respiratory tract (ID 1714, 1715) pursuant to Article 13(1) of Regulation (EC) No 1924/2006
Favorable effect of dietary vitamin C on bone mineral density in postmenopausal women (KNHANES IV, 2009): discrepancies regarding skeletal sites, age, and vitamin D status
The relation of dietary vitamin C intake to bone mineral density: results from the PEPI study
DIETARY SUPPLEMENT: VITAMIN C
Emotional balance ✪✪✪✪✪
Ascorbate is involved in neurotransmitter synthesis. It is a necessary cofactor for the biosynthesis of norepinephrine from dopamine and for the hydroxylation of tryptophan to produce serotonin. It also acts as a modulator of glutamatergic, cholinergic and GABAergic transmission. The European health authorities (EFSA, the European Food Safety Authority and the European Commission) have concluded that products containing vitamin C (ascorbic acid) may claim to contribute to the normal functioning of the nervous system and to normal mental function.
Posologie
Oral administration
95 mg
Impaired adrenal catecholamine system function in mice with deficiency of the ascorbic acid transporter (SVCT2)
Vitamin and mineralrequirementsin human nutrition
Vitamin C function in the brain: vital role of the ascorbate transporter SVCT2
DIETARY SUPPLEMENT: VITAMIN C
Oxidative stress ✪✪✪✪✪
At physiological concentrations, vitamin C is the most effective aqueous antioxidant in plasma, interstitial fluids and the soluble phases of cells. Vitamin C acts as a powerful free radical scavenger in plasma, protecting cells against oxidative damage caused by reactive oxygen species (ROS). It traps oxygen and nitrogen free radicals such as superoxide, hydroxyl, peroxyl and nitroxide radicals, as well as non-radical reactive species such as singlet oxygen, peroxynitrite and hypochlorite. In addition to its direct antioxidant function, it also indirectly enhances free radical scavenging by regenerating vitamin E and maintaining glutathione in its reduced form. Vitamin C decreases oxidants in gastric juice, reduces lipid peroxidation and lowers oxidative damage to DNA and proteins.
Posologie
Orally
95 mg
Influence of vitamin C on markers of oxidative stress in the earliest period of ischemic stroke
Supplementation of ascorbic acid and alpha-tocopherol is useful to preventing bone loss linked to oxidative stress in elderly
Effect of vitamin C supplementation on postprandial oxidative stress and lipid profile in type 2 diabetic patients
Does vitamin C supplementation influence the levels of circulating oxidized LDL, sICAM-1, sVCAM-1 and vWF-antigen in healthy male smokers?
High dosage of ascorbic acid and alpha-tocopherol is not useful for diminishing oxidative stress and DNA damage in healthy elderly adults
UV exposure ✪✪✪✪✪
According to a study, topical application of vitamins E and C, combined with melatonin, showed a modest photoprotective effect when used before UV exposure, but had no effect when used during or after UV exposure.rnrn
Posologie
Topical application
Modulation of UV-light-induced skin inflammation by D-alpha-tocopherol and L-ascorbic acid: a clinical study using solar simulated radiation.
Effect of topical antioxidants on UV-induced erythema formation when administered after exposure.
Topical melatonin in combination with vitamins E and C protects skin from ultraviolet-induced erythema: a human study in vivo.
Gout ✪✪✪✪✪
Clinical studies report that daily consumption of 500 to 1500 mg of vitamin C is associated with a 17% to 34% reduced risk of gout compared with subjects who consume less than 250 mg per day. Additionally, people who consume more than 500 mg of vitamin C per day have serum uric acid levels lower by 0.5 to 0.6 mg/dL compared with those who consume less than 90 mg per day. However, daily intake of 500 mg of vitamin C for 8 weeks does not lower serum uric acid levels in patients suffering from gout. Thus, vitamin C may help prevent the development of gout, but cannot help treat the disease.rnrn
Posologie
Oral administration
500 - 1500 mg
Cold ✪✪✪✪✪
There is considerable controversy over the effectiveness of vitamin C for treating the common cold. The majority of the evidence shows that taking high doses of oral vitamin C can reduce the duration of cold symptoms by 1 to 1.5 days in some patients. Other studies have found no effect with doses up to 3 grams per day. Some clinical data suggest that vitamin C supplementation reduces the incidence of colds in individuals exposed to physical stress but not in the general population. A dose of 1 to 3 grams per day has been used for the common cold, although doses of 2 g and above appear to be more effective than lower doses.
Posologie
Oral
2 - 3 g
Effect of Vitamin C on Common Cold: Randomized Controlled Trial
Vitamin C supplementation and common cold symptoms: problems with inaccurate reviews.
The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections.
Vitamin C, the placebo effect, and the common cold: a case study of how preconceptions influence the analysis of results.
Ascorbic acid and the common cold: reviewing the evidence.
Vitamin C for preventing and treating the common cold.
Hypercholesterolemia ✪✪✪✪✪
Analysis of clinical research suggests that taking 500 mg of vitamin C per day for at least 4 weeks reduces low-density lipoprotein (LDL) cholesterol by about 8 mg/dL and reduces triglycerides by about 20 mg/dL in patients with hypercholesterolemia. Furthermore, vitamin C does not appear to reduce cholesterol levels in patients with normal cholesterol.
Posologie
Oral
500 mg
4 - weeks
Long-term vitamin C supplementation has no markedly favorable effect on serum lipids in middle-aged Japanese subjects.
Vitamin C supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials.
Arterial hypertension ✪✪✪✪✪
Taking 500 mg of vitamin C orally with conventional antihypertensive medications appears to further lower systolic blood pressure, but effects on diastolic pressure are contradictory. However, daily intake of 500 mg of vitamin C without antihypertensive treatment does not appear to reduce systolic or diastolic blood pressure.
Posologie
Oral
500 mg
Vitamin C: update on physiology and pharmacology
Role of vitamin C in the function of the vascular endothelium. May JM1, Harrison FE.
Treatment of hypertension with ascorbic acid.
Is vitamin C an effective antihypertensive supplement? A review and analysis of the literature.
Ascorbic acid reduces blood pressure and arterial stiffness in type 2 diabetes.
The combination of vitamin C and grape-seed polyphenols increases blood pressure: a randomized, double-blind, placebo-controlled trial.
AMD ✪✪✪✪✪
Supplementation with antioxidants including vitamins A (15 mg), C (500 mg), E (400 IU) combined with zinc (80 mg) reduces the risk of vision loss by 27% and slows disease progression in patients at high risk of developing age-related macular degeneration (AMD).
Posologie
Oral
500 mg
10 years
Synergies
Long-term effects of vitamins C and E, beta-carotene, and zinc on age-related macular degeneration: AREDS report no. 35.
Age-Related Eye Disease Study Research Group. Potential public health impact of age-related eye disease study results: AREDS report no. 11.
Wrinkles ✪✪✪✪✪
Topical preparations containing 5% to 10% vitamin C appear to improve wrinkles. In a clinical trial, a topical preparation containing 10% vitamin C in the form of L-ascorbic acid with acetyl tyrosine, zinc sulfate, sodium hyaluronate and bioflavonoids applied to the face for 3 months improved wrinkles and skin tone compared with placebo. There is also evidence that 3% vitamin C applied for 12 weeks can reduce facial wrinkles.rnrnIn another clinical study, vitamin C was also applied topically as a patch containing 5.6% vitamin C, every 4 days for 12 weeks, to the crow's feet on one side of the face. The patch reduced wrinkles compared with the control treatment applied to the contralateral side of the face.rnrnFinally, a recent study conducted in women aged 30 to 65 years shows that the application of a liquid containing 20% vitamin C, 0.0005% raspberry leaf cell culture extract and 1% vitamin E to the face every night for 8 weeks improves skin color, elasticity, radiance, smoothness and the appearance of wrinkles compared with the usual face products used alone.
Posologie
Topical, oral
3 months
vitamin C-based cream
Evaluation of the anti-wrinkle effect of a lipophilic pro-vitamin C derivative, tetra-isopalmitoyl ascorbic acid
Anti-aging and brightening effects of a topical treatment containing vitamin C, vitamin E, and raspberry leaf cell culture extract: A split-face, randomized controlled trial
Use of topical ascorbic acid and its effects on photodamaged skin topography.
Topical activity of ascorbic acid: from in vitro optimization to in vivo efficacy.
Skin healing ✪✪✪✪✪
Vitamin C is important for effective wound healing, because a deficiency contributes to fragility of granulation tissue and thus impedes the healing process. In vitro studies with skin graft samples have shown that vitamin C prolongs cell viability, promotes formation of an epidermal barrier, and supports grafting. Thus, vitamin C is used to improve wound healing before surgical intervention.
Posologie
Orally
Vitamin C and human wound healing
Vitamin C Regulates Keratinocyte Viability, Epidermal Barrier, and Basement Membrane In Vitro, and Reduces Wound Contraction After Grafting of Cultured Skin Substitutes
The importance of patients' nutritional status in wound healing
Osteoarthritis ✪✪✪✪✪
Dietary intake of vitamin C by subjects suffering from osteoarthritis appears to slow disease progression. Clinical research also suggests that taking vitamin C in the form of calcium ascorbate at a dose of 1 gram per day for 2 weeks significantly reduces the pain and severity of osteoarthritis compared with placebo, although the effects are smaller than those observed with nonsteroidal anti-inflammatory drugs (NSAIDs).
Posologie
Orally
1 g
2 weeks
calcium ascorbate
Synergies
Allergic rhinitis ✪✪✪✪✪
The epidemiological study shows that high plasma levels of vitamin C are not associated with a decreased risk of allergic rhinitis. However, clinical research shows that the nasal form of vitamin C administered three times a day for 2 weeks reduces nasal secretions, obstruction and nasal edema in 74% of patients with allergic rhinitis.rnrn
Posologie
By nasal route
2 - weeks
Spray
Osteoporosis ✪✪✪✪✪
Some data suggest that vitamin C intake may be related to bone mineral density in premenopausal women. In postmenopausal women who take estrogens and smoke, higher vitamin C levels may reduce fracture risk. However, in menopausal women without a history of smoking or estrogen use, higher serum vitamin C levels have been associated with lower bone mineral density. At present, there is not enough information to make recommendations about vitamin C and bone density.rnrn
Posologie
Orally
1 g
Cancer ✪✪✪✪✪
The relationship between vitamin C and the prevention and treatment of cancer has been the subject of extensive research, highlighting its potential. Historically, increased consumption of fruits and vegetables rich in vitamin C has been linked to a reduced risk of several non–hormone-dependent cancers. Epidemiological studies have shown a significant protective effect of vitamin C, particularly against cancers of the gastrointestinal system, the lung, and in some cases, the breast and prostate. Linus Pauling’s research on the administration of high doses of vitamin C by intravenous route marked a turning point, proposing therapeutic potential in the treatment of advanced cancers. These studies suggest that vitamin C could improve quality of life and certain objective markers in patients with terminal cancer. However, the lack of randomized controlled trial design in their studies has raised criticism about the validity of their findings. More recent studies have produced conflicting evidence on the efficacy of vitamin C in reducing cancer progression, with results varying according to the route of administration (oral vs intravenous) and patients’ baseline vitamin C levels. Although high concentrations of vitamin C achieved by intravenous administration have shown selective cytotoxicity against cancer cell lines, clinical trials have not always confirmed these observations. The debate over the use of vitamin C in oncology continues, with some studies suggesting benefits as an adjunct to standard treatments, while others warn of potential interactions with certain therapies, such as the inactivation of bortezomib (a drug used in the treatment of certain types of cancer). A long-term intake of at least 80–110 mg of vitamin C per day is associated with significant reductions in the risk of certain cancers. Supplementation for patients with terminal cancer: 10 g/day of oral vitamin C (although it has not shown a significant difference in patient outcomes). Intravenous administration of 150–710 mg/kg/day of vitamin C for up to 8 weeks.
Posologie
Oral, intravenous
80 - 110 mg
Properties
Antioxidant
Vitamin C is one of the four dietary antioxidants along with vitamin E, beta-carotene and selenium, and participates in the breakdown of oxygen-derived free radicals, which provides protection against toxic agents to the cell. Thus, it reduces oxidants in gastric juice, lipid peroxidation, and oxidative damage to DNA and proteins.
Usages associés
Essential
Vitamin C is involved in numerous biochemical reactions through a hydroxylation mechanism. Its role in collagen synthesis is important. Vitamin C deficiency leads to an alteration of collagen structure. This explains the clinical manifestations of scurvy (a disease caused by vitamin C deficiency): impaired dentin formation and tooth loss, damage to the vascular wall and purpura with hemorrhagic syndrome, edema, skin alteration due to keratin involvement, and bone remodeling. On the other hand, vitamin C acts as a cofactor in the synthesis of catecholamines, notably in the conversion of dopamine to norepinephrine, which may explain the behavioral and mood disorders observed during scurvy. Other actions have been described: involvement in the catabolism of phenylalanine and tyrosine (amino acids), in the conversion of cholesterol to bile acids, increased metabolism of toxins and carcinogens by hepatic cytochrome P450, and absorption of non-heme iron (not incorporated into the heme structure).
Usages associés
Neurological
Ascorbate is involved in neurotransmitter synthesis. It is a cofactor necessary for the biosynthesis of norepinephrine from dopamine and for the hydroxylation of tryptophan to produce serotonin. It also acts as a modulator of glutamatergic, cholinergic, and GABAergic transmission. Additionally, it is involved in neuronal maturation and acts as a neuroprotective agent.
Energy booster
Vitamin C appears to be readily absorbed and stored in skeletal muscle tissue, where it may provide antioxidant protection and may support the biosynthesis of carnitine and collagen. In addition, a decrease in biomarkers of muscle damage has been observed.
Usages associés
Dermatological effect
It is thought that vitamin C plays a role in neutralizing free radicals generated in the skin following exposure to ultraviolet rays, which cause photoaging of the skin. Topical application of vitamin C before UV exposure is believed to prevent skin damage due to the antioxidant effects of vitamin C. Furthermore, topical application of vitamin C has been shown to increase collagen production and improve its organization.
Usages associés
Cardiovascular
In people with chronic heart failure, vitamin C appears to improve endothelial dysfunction and arterial dilation by preventing the inactivation of nitric oxide (NO)-mediated vasodilation. Vitamin C also appears to improve endothelial function and vascular resistance in patients with chronic kidney failure. Some researchers believe that vitamin C may prevent or slow atherosclerosis by inhibiting low-density lipoprotein (LDL) cholesterol, scavenging oxygen-derived free radicals in vascular cells, and limiting cellular responses to oxidized LDL, such as the production of endothelium-derived NO. There is evidence that vitamin C reduces LDL cholesterol levels in patients with hypercholesterolemia; however, taking vitamin C does not appear to lower serum lipid levels in people with normal lipid levels.
Usages associés
Anti-inflammatory
Some research suggests that vitamin C may reduce levels of C-reactive protein (CRP) (a protein produced in response to inflammation) in subjects actively or passively exposed to tobacco smoke.
Usages associés
Immune stimulant
Vitamin C appears to increase T-lymphocyte activity, phagocyte function, leukocyte mobility, and possibly antibody and interferon production. In addition, some researchers believe that vitamin C levels in white blood cells decrease at the onset of a cold and that increasing vitamin C intake may be beneficial.
Usages associés
Uricosuric effect
Vitamin C is thought to lower serum uric acid levels through a uricosuric effect. Some research shows that uric acid clearance in healthy subjects taking vitamin C increases by more than 200% within 2 to 6 hours. Indeed, vitamin C may compete with uric acid during renal reabsorption.
Usages associés
Remineralizing
Although the relationship between calcium, vitamin D, and bone mineral density is well known, other nutrients such as vitamin C are also essential for the development, repair, and maintenance of bone. Epidemiological studies have shown a positive association between bone density and vitamin C intake. Low vitamin C intakes have been associated with decreased mineral density, particularly at the femoral neck and hip. Data collected from 13,080 adults from 1988 to 1994 identified an association between dietary and serum ascorbic acid, bone mineral density, and bone fracture.
Usages associés
Anticancer
Vitamin C is selectively cytotoxic to many cancer cell lines and has anticancer activity in vivo. It is important to note that pharmacological concentrations of ascorbic acid (0.3-20 mmol/L) are needed to find evidence of cytotoxicity in vitro and in vivo, whereas physiological concentrations of ascorbic acid (0.1 mmol/L) have no effect on tumor or normal cells. The most reliable method to achieve these high doses is intravenous (IV) administration of vitamin C rather than the oral route, which has limited absorption. The effect appears to be dose-dependent and operates through several mechanisms, such as immunomodulation, inhibition of cell division and growth, gene regulation, and induction of apoptosis. The mechanism of cytotoxicity demonstrated in several models is the ability of ascorbate at pharmacological concentrations to exert pro-oxidant activity, generating hydrogen peroxide-dependent cytotoxicity against a variety of cancer cells in vitro and in vivo without adversely affecting normal cells. One possible explanation for the preferential targeting of tumor cells concerns their overexpression of GLUTs, which transport dehydroascorbic acid. The latter accumulates in tumor cells and leads to an increase in intracellular hydrogen peroxide levels.
Usages associés
Anti-aging
Free radicals are generated in the skin after exposure to ultraviolet (UV) radiation and cause photo-induced aging. Vitamin C in the skin is thought to play a key role in neutralizing free radicals and reducing UV-induced skin damage, and therefore topical application of vitamin C prevents skin damage when applied before UV exposure. Topical preparations are also believed to help treat photo-aged and wrinkled skin by increasing collagen production and improving collagen organization. Topical preparations containing 10% vitamin C may be the most effective at increasing vitamin C concentrations in the skin.
Usages associés
Antiallergic
Some evidence suggests that low levels of vitamin C are associated with higher plasma levels of histamine. Theoretically, people with low vitamin C levels may experience more severe symptoms of allergic rhinitis. There is also evidence that vitamin C may have mild antihistamine properties. Indeed, ascorbic acid is involved in histamine metabolism, acting with Cu2+ to inhibit its release and enhance its breakdown.
Usages associés
Safe dosage
Adult (18 years and older): 95 mg
EFSA defined the intake level likely to meet the daily needs of nearly all individuals in an apparently healthy population. The maximum chronic daily intake is not set by EFSA.
Child (1 to 3 years): 20 mg
Pregnant women (18 years and older): 105 mg
Infant (7 to 11 months): 20 mg
Child (11 to 14 years): 70 mg
Child (15 to 17 years): 90 mg
Breastfeeding women (18 years and older): 155 mg
Child (4 to 6 years): 30 mg
Child (7 to 10 years): 45 mg
Interactions
Médicaments
Anticancer drugs: moderate interaction
The use of antioxidants such as vitamin C is controversial. Indeed, they may reduce the effectiveness of chemotherapy by neutralizing free radicals. However, some researchers believe that antioxidants can make chemotherapy more effective by inducing oxidative stress that can act on dying or cancerous cells.
Estrogens: moderate interaction
Combining vitamin C with oral contraceptives may increase estrogen levels by 55%. It is thought that vitamin C prevents the oxidation of estrogens in tissues, regenerates oxidized estrogens, and reduces the conjugation of estrogens to sulfate in the intestinal wall. These effects are not observed when tissue vitamin C levels are high.
Fluphenazine: moderate interaction
A case of a significant decrease in fluphenazine levels was noted during vitamin C supplementation (500 mg twice daily). The mechanism is not yet known.
Indinavir: moderate interaction
Taking oral doses of vitamin C together with indinavir may reduce indinavir levels. The mechanism of this interaction is not yet known.
Warfarin: moderate interaction
High doses of vitamin C may reduce the response to warfarin, by causing diarrhea or reducing warfarin absorption.
Plantes ou autres actifs
Vitamin C: moderate interaction
Vitamin C can increase the amount of aluminum absorbed. It is thought that vitamin C chelates aluminum, keeping it in solution and promoting its absorption. In people with normal kidney function, urinary excretion of aluminum is likely increased, which reduces aluminum toxicity. However, people with renal impairment who chronically take aluminum-containing compounds should avoid high-dose vitamin C supplementation.
Vitamin C: moderate interaction
Vitamin C increases iron absorption.
Precautions
Alzheimer's disease: use with caution
Clinical research has shown that the combination of 500 mg vitamin C, 800 mg vitamin E, and 900 mg alpha-lipoic acid may worsen cognitive decline compared with placebo in patients with mild to moderate Alzheimer's disease.
Cancer: use with caution
Cancer cells accumulate high concentrations of vitamin C. Indeed, they absorb the oxidized form (dehydroascorbic acid) and then convert it back into vitamin C. The effect of this phenomenon on cancer cells is still unknown. However, cancer patients should not use high doses of vitamin C before consulting their oncologists.
Type 2 diabetes: use with caution
Vitamin C may affect glycogenolysis by increasing blood glucose. However, this effect remains controversial. In postmenopausal women with diabetes, supplementation with 300 mg/day of vitamin C is associated with an increased risk of cardiovascular mortality.
Transplantation: use with caution
Chronic use of high-dose vitamin C before kidney transplantation may increase the risk of graft loss or delay graft function.
Kidney stones: avoid
Vitamin C can cause precipitation of urate, cystine, or oxalate stones.rnrn
Hemochromatosis: avoid
Vitamin C supplementation can exacerbate iron toxicity by mobilizing iron stores.rnrn
G6PD deficiency: avoid
Large amounts of vitamin C can cause hemolysis in people with glucose-6-phosphate dehydrogenase (G6PD) deficiency.rnrn
