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19 Benefits and Side Effects of Vitamin C (13 Contraindications To Be Noted)

Vitamin C also known as ascorbic acid, is a carbohydrate converted from glucose, the appearance is white crystal, is weakly acidic and sour, is the most important water-soluble vitamin in the human body, most mammals can synthesize from the body on their own, but human beings due to genetic mutation, can not make their own, must be ingested from food.

In the human body, vitamin C has a variety of functions, the most important of which are several, including antioxidant, anti-inflammatory, antiviral, antibacterial, collagen production, etc., which are also the basic conditions for maintaining health, because the fight against disease is closely related to these factors.Note 11

The reason why vitamin C is popular around the world is from the strong advocacy of two-time Nobel laureate Linus Pauling, in his best-selling book: Vitamin C and the Common Cold, began to change the world’s view of vitamin C, since then vitamin C is often used to treat colds and daily health care, becoming a necessary health supplement for American families

Vitamin C: The Real Story by two medical doctors in the United States also mentions that Vitamin C is a superior molecule with a key impact on health.)

What are the benefits of vitamin C in empirical medicine? Are there any side effects of vitamin C? See text analysis for details

When is vitamin C most effective?

The body does not naturally produce or store water-soluble vitamins. Therefore, these vitamins need to be taken from dietary sources or supplement sources.

Water-soluble vitamins are best absorbed on an empty stomach. This means that 30 minutes before a meal, or two hours after a meal is the most suitable time.

However, for people with poor gastrointestinal function, do not supplement too much vitamin C (especially the acidic ascorbic acid form) on an empty stomach, if excessive is easy to cause gastrointestinal irritation.

People with poor gastrointestinal function or acid-phobia can switch to acid-free vitamin C, and related forms include: liposomal vitamin C, sodium ascorbate, calcium ascorbate, ascorbyl palmitate.

Which is the best absorption rate of natural or synthetic vitamin C?

In the growing supplement market, vitamin C supplements come in many different forms, but can be broadly divided into naturally derived and synthetic.

In terms of chemical structure, natural and synthetic vitamin C (ascorbic acid) are the same, and there is no known difference in biological activity.

In at least two human trials, bioavailability differences between naturally derived and synthetic L-vitamin C (L-ascorbic acid) were studied, and no clinically significant difference was found. Note 1Note 2

In addition, since the nutrients in natural foods are not single, studies have pointed out that if ingested with other nutrients, such as bioflavonoids, vitamin E, etc., they can produce complementary synergies and improve each other’s bioavailability.

What are the proven benefits of vitamin C recommendations?

1. Vitamin C improves postoperative pain

In patients undergoing outpatient surgery, pain is the most common cause of delayed discharge (occurring in about 80%), second only to drowsiness and digestive discomfort (i.e., nausea and vomiting).

Postoperative pain not only affects the patient’s surgical outcome, well-being and satisfaction with medical care, but may also cause rapid heartbeat, hyperventilation, decreased alveolar ventilation, transition to chronic pain, poor wound healing, insomnia etc.

A systematic literature review and meta-analysis (7 RCTs with 519 participants) noted that pain scores and opioid consumption were lower in the vitamin C group than in the placebo group after surgery (1 to 2 hours) and at 24 hours. Note 1

Subgroup analyses showed that the effect of reducing pain severity and opioid requirements (immediately postoperatively (1-2 hours) and within 24 hours) was more significant in patients receiving intravenous vitamin C, but the oral route did not have a similar effect.

*Conclusion: The use of vitamin C (intravenously) may help reduce severe postoperative pain and opioid demand, and more large-scale trials are needed given its effectiveness and low toxicity given intravenous administration

2. Vitamin C is good for periodontitis

Periodontitis is an inflammatory disease of tooth-supporting tissues caused by a specific microbiota, leading to progressive destruction of periodontal ligaments and alveolar bone, the formation of periodontal pockets, receding gums, or both.

This type of periodontal disease affects about 20% to 50% of the global population. Risk factors such as smoking, poor oral hygiene, diabetes, medications, age, genetics, and stress are all associated with periodontal disease development.

Periodontal disease is often associated with systemic diseases such as cardiovascular disease, diabetes and adverse pregnancy outcomes, which may lead to a 19% increased risk of cardiovascular disease, and people with type 2 diabetes with severe periodontal disease have a 3.2-fold higher risk of death than those with no or mild periodontitis.

A systematic review (6 randomized controlled trials) noted that vitamin C supplementation helped improve bleeding index in people with gingivitis, but did not significantly reduce probing depth or clinical attachment gain in patients with periodontitis. Note 2

*Conclusion: Vitamin C as an adjunct to non-surgical periodontal treatment does not significantly improve the depth of periodontal pocket exploration, and more long-term, well-designed studies are needed to further validate this due to the limited evidence available

3. Vitamin C is beneficial for sepsis

Sepsis is a life-threatening clinical condition with extensive physiological and biochemical abnormalities. Sepsis/sepsis is now defined as “organ dysfunction caused by a dysfunctional host response to infection”, emphasizing for the first time the key role of innate and adaptive immune responses in the development of clinical syndromes.

About 49 million people are infected with sepsis each year, and an estimated 1100 million people die from the syndrome, accounting for 19.7% of deaths worldwide.

A meta-analysis (23 randomized controlled trials, 2712 patients with sepsis) found that regimens containing vitamin C were associated with reduced mortality, SOFA score, and duration of vasopressor demand (no significant difference in length of hospital stay or ICU stay) compared with controls. Note 1

*Conclusion: Vitamin C intravenous regimens may be beneficial for sepsis, but due to the high heterogeneity of the samples included, more studies are needed to confirm efficacy, dose, route, and timing of administration

4. Vitamin C reduces uric acid levels

Hyperuricemia is generally defined as a serum uric acid concentration above 7 mg/dl, occurring in approximately 8.9% to 24.4%.

Can be divided into symptomatic (with symptoms of gout, urolithiasis, or acute uric acid nephropathy) and asymptomatic (defined as elevated serum uric acid levels without any of these symptoms).

Although most asymptomatic patients never experience changes attributable to urate crystal deposition, elevated serum uric acid levels have been found to lead to tissue damage and increase the incidence of hypertension, dyslipidemia, obesity, metabolic syndrome, type 2 diabetes, cardiovascular disease, and chronic kidney disease.

A meta-analysis of 16 randomized controlled trials with 1,013 participants suggested that vitamin C supplementation (average dose and duration of 500 mg daily for 30 days) helped reduce serum uric acid values. Note 1

In addition, subgroup analyses found that the effect was most significant in particular when the mean age of participants was < 65 years, placebo or no treatment, trial duration < 1 month, and high-quality studies.

The mechanism behind it is related to vitamin C to promote the excretion of uric acid by the kidneys and reduce the formation of free radicals.

*Conclusion: Oral vitamin C may have a positive effect on uric acid reduction, but due to the high heterogeneity of the samples included, more studies are needed to further validate

5. Vitamin C is beneficial for the 2019 novel coronavirus disease

Caused by severe acute respiratory syndrome coronavirus 2019 (SARS-CoV-19), COVID-2 has had a catastrophic impact on global public health, with the number of infections continuing to rise globally since the first confirmed case due to its highly contagious nature.

Compared with influenza, SARS-CoV-2 is more likely to cause respiratory complications (eg, severe pneumonia, acute respiratory distress syndrome, interstitial pneumonia) in 10% to 15% of cases, and in addition, 5% of infected patients require admission to an intensive care unit, with an estimated mortality rate of 0.7% to 7%.

In clinical practice, supportive interventions and a variety of treatments such as immunomodulators, antiviral therapy, antibiotics, antimalarial drugs, and convalescent plasma transfusion-related techniques have been widely used.

One randomised controlled trial (150 2019 patients infected with the novel coronavirus) was divided into two groups, with intravenous vitamin C (50 mg/kg/day) plus standard care in the intervention group and standard care only in the placebo group (including antipyretic, dexamethasone, and prophylactic antibiotics). Note 1

It was found that patients who received intravenous VC were asymptomatic earlier (7.1±1.8 days vs 9.6±2.1 days) and had fewer hospital days (8.1±1.8 days vs 10.7±2.2 days) compared with those who received standard care alone.

However, there was no significant difference between the two groups in mechanical ventilation and mortality.

*Conclusion: For patients infected with the new coronavirus in 2019, intravenous vitamin C may help improve clinical symptoms and reduce hospital stay, but limited by the small sample size, more and larger studies are needed for further verification

6. Vitamin C reduces C-reactive protein

C-reactive protein is an acute phase protein that is a biomarker of the inflammatory process.

Serum levels are elevated in inflammatory or stressful reactions such as coronary heart disease, trauma, arthritis, and surgical injury.

Existing clinical studies have shown that C-reactive protein levels correlate with the early stages of coronary artery disease and are considered a potential predictor of future cardiovascular disease.

A systematic literature review and meta-analysis (12 randomized controlled trials, 446 participants) noted that vitamin C supplementation had a significant reduction in C-reactive protein levels. Note 1

In addition, the associated reduction of hs-CRP (hypersensitivity C-reactive protein) was most pronounced in subjects such as baseline CRP levels ≥3, age < 60 years, or intravenous vitamin C.

*Conclusion: Vitamin C supplementation has a positive effect on reducing inflammatory index C-reactive protein, but due to heterogeneity between studies, more trials are needed to support this

7. Vitamin C is beneficial for motor bronchospasm

Exercise-induced bronchoconstriction, defined as acute airway narrowing (transient and reversible) that occurs during or after exercise and can be observed in patients with or without chronic asthma (reported to usually occur within 2 to 5 minutes after exercise, peaking after 10 minutes and subsiding after about 60 minutes).

Typical symptoms include difficulty breathing, wheezing, coughing, chest tightness, increased mucus, or feeling unwell when you’re well.

A systematic literature review and meta-analysis (3 double-blind, placebo-controlled randomized trials with 40 participants) showed that taking vitamin C (0.5 to 2 g at a dose of 0.5 to 2 g) before exercise reduced the value of forced expiratory volume per second (FEV1) after exercise (by about 50%). Note 2

*Conclusion: Pre-exercise vitamin C may be a positive benefit for exercise-induced bronchospasm, but more large trials are needed to confirm its clinical benefit

8. Vitamin C is beneficial for essential hypertension

Essential hypertension, characterized by chronically elevated blood pressure for unknown reasons, affects nearly 95 percent of people with high blood pressure.

Multiple environmental factors, such as smoking, socioeconomic status, stress, high-salt diet, obesity, and vitamin D deficiency, have been shown to play a role in the onset.

These factors cause essential hypertension through epigenetic and genetic interactions, or by inducing specific gene expression.

A systematic literature review and meta-analysis (8 randomized controlled trials with 614 participants with essential hypertension) noted that oral vitamin C (daily doses ranging from 300 mg to 1000 mg, duration of intervention ranging from 4 weeks to 24 weeks) helped reduce systolic and diastolic blood pressure. Note 1

In addition, subgroup analysis showed that the relevant blood pressure regulation effect was most significant in subjects older than 60 years, doses greater than 500 mg, and intervention periods greater than 6 weeks.

*Conclusion: For patients with essential hypertension, oral vitamin C has a positive effect on blood pressure regulation, but limited by the small sample size, more large trials are still needed to support it

9. Vitamin C is good for the common cold

The Common Cold, also known as respiratory viral infection, is a spontaneous relief upper respiratory tract infection characterized by a runny nose, nasal obstruction, headache, sneezing, cough, and fever (usually < 37.8°C), with total symptoms lasting between 7 – 14 days.

About 30 to 50 percent of cold symptoms are caused by rhinoviruses, and bacterial infections are rare.

According to the World Health Organization, the common cold records 1 million visits a year in the United States, at $77.<> billion in related costs (mostly for over-the-counter medications).

A meta-analysis (9 randomized placebo-controlled trials) suggests that taking an extra higher dose of vitamin C (3 to 4 grams per day) at the beginning of a cold can help shorten the duration of illness and stay indoors, and relieve symptoms of the common cold, including chest pain, fever and chills, provided that small-dose vitamin C is supplemented regularly (1 gram or less per day). Note 1

For people who do not supplement regularly on weekdays, sudden increases in high doses of vitamins in the presence of colds are not significantly helpful.

Another meta-analysis (9 randomized controlled trials, 3135 children aged 3 months to 18 years) noted that although oral vitamin C had no significant effect on preventing upper respiratory tract infection compared with placebo, it helped reduce the duration of upper respiratory tract infection (about 1.6 days). Note 2

The mechanism behind it may be related to vitamin C activation of the immune system, such as natural killer cell activity, lymphocyte proliferation, chemotaxis and delayed hypersensitivity, and can enhance the secretion of sympathetic nervous system and adrenaline during stressful conditions.

*Conclusion: The effectiveness of oral vitamin C in preventing colds is still controversial, but the use of therapeutic doses of vitamin C (3 to 4 grams per day) at the beginning of a cold may help shorten the duration and severity of symptoms

10. Vitamin C is beneficial for blood sugar control

Diabetes is a chronic condition in which absolute or relative deficiency of insulin is due to impaired insulin production and action, associated risk factors include: family history, obesity, chronic lack of exercise, ethnicity, history of impaired fasting blood glucose, impaired glucose tolerance, glycated hemoglobin, hypertension, abnormal HDL cholesterol, or elevated triglyceride levels.

In the long term, these metabolic abnormalities can lead to complications such as cardiovascular disease, retinopathy, kidney disease, and neuropathy.

A systematic literature review and meta-analysis (24 randomized controlled trials, 937 participants) noted that, overall, oral vitamin C did not alter glucose, glycated haemoglobin, and insulin concentrations. Note 1

However, stratified analysis showed that vitamin C had an effect on lowering blood glucose levels in older participants with type 2 diabetes lasting longer than 30 days.

*Conclusion: The glycemic regulatory benefits of vitamin C supplementation vary greatly depending on study design and participant characteristics, with the associated improvement effect being most pronounced in diabetes, older adults, and long-duration studies

11. Vitamin C is beneficial to improve hyperlipidemia

In the United States, more than 1 million people (about 53% of adults) have abnormal cholesterol levels, however, less than 50% of patients receive treatment, and less than 35% of those treated achieve adequate control.

Modifiable risk factors for hyperlipidemia include a diet high in saturated or trans fats, physical inactivity, smoking, and obesity, with secondary causes including biliary obstruction, chronic kidney disease, type 2 diabetes, hypertension, and hypothyroidism.

A systematic literature review and meta-analysis (40 randomized controlled trials, 1981 participants) noted that overall, vitamin C supplementation had no clear effect on blood lipids. Note 1

However, further subgroup and sensitivity analyses showed significant lipid improvement (lowering total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglycerides, and increasing high-density lipoprotein cholesterol (HDL-C)) in subjects with dyslipidemia or low vitamin C levels.

*Conclusion: Additional vitamin C supplementation may be beneficial in improving blood lipids, especially in subjects with dyslipidemia or low vitamin C levels

12. Vitamin C anti-anxiety

Anxiety is a state of mind, physiology, and behavior, whether actual or latent, triggered by an event that threatens overall well-being or survival.

However, persistent excessive anxiety (and avoidance) is generally referred to as anxiety disorders, especially when there is no real danger. According to recent epidemiological studies, the lifetime prevalence of any form of anxiety disorder can reach 28.8%.

A randomized, double-blind, placebo-controlled trial (142 students) showed that vitamin C (1000 mg) intake had short-term anxiolytic effects in people with high trait anxiety. Note 1

*Conclusion: For subjects with high trait anxiety, the use of vitamin C may have the effect of regulating mood and alleviating anxiety, but limited by sample size, more extensive population studies are needed to comment on clinical relevance

13. Vitamin C is beneficial for cognitive function

As a result of medical advances and improvements in the quality of care, life expectancy has increased dramatically, but with it comes the exposure to numerous ageing-related diseases.

According to the United States research survey, the prevalence of dementia among the elderly over 71 years old is about 13.9%, of which 69.9% is Alzheimer’s disease and vascular dementia accounts for 17.4%.

A generational study (Cohort Study) found that subjects with the highest blood concentrations of vitamin C had lower rates of cognitive impairment (even after adjusting for gender, race, and smoking). Note 1

In addition, more standard body weight, BMI, waist circumference, and standard metabolic values such as glycosylated hemoglobin, insulin, and triglycerides were also observed in this population.

*Conclusion: Blood vitamin C concentration is associated with cognitive function, but more research is needed to confirm the association with dietary intake

14. Vitamin C is good for cardiovascular health

Cardiovascular disease, generally known as heart disease, is a disease of insufficient blood flow of blood vessels causing hypoxia of heart tissue, often including angina, myocardial infarction and heart failure, etc., its terrible thing is that there are almost no symptoms, and after the sudden there is a fatality rate of up to 3%, is a major killer who instantly kills people

A prospective study (follow-up period of 12.8 years, sample size of 20299 people) showed that those with the highest blood concentration of vitamin C (compared to the lowest) reduced the risk of heart failure by 24%. Each 20 μmol/L increase in blood vitamin C concentration reduced the risk value by 9% (range 23-82 μmol/L).Note 1

Another meta-analysis (including 44 clinical trials) also found that vitamin C intake helped improve endothelial function, and vascular endothelial dysfunction is considered to be an important factor in cardiovascular disease.Note 2

15. Vitamin C to prevent atrial fibrillation

Atrial fibrillation is a common postoperative complication after cardiac surgery, ranging from 25% of coronary artery bypass grafting to 65% of valve replacement surgery, which may lead to acute myocardial infarction, ischemic stroke and acute renal failure, greatly increasing the medical burden, length of hospital stay and mortality.

A systematic literature review and meta-analysis (15 studies, 2050 participants) showed that vitamin C (oral or intravenous) reduced the incidence of atrial fibrillation after cardiac surgery or rhythm conversion by 27% and the length of hospital stay by 10%. Note 1

*Conclusion: Vitamin C may have the effect of reducing the incidence of atrial fibrillation in high-risk populations, but more empirical confirmation is needed due to high heterogeneity between studies

16. Vitamin C reduces the incidence of hip fractures

Hip fractures are one of the most serious bone problems in people over the age of 65, with multiple complications after bed rest, such as pressure ulcers, deep vein thrombosis, pneumonia and urinary tract infections. Hip fractures increase the risk of death in the first 3 months by 3 to 8 times compared to the general population.

A meta-analysis (6 studies with more than 10,000 participants) showed that those who consumed the most vitamin C were 27% less likely to have hip fractures compared with those who consumed the least vitamin C. Note 1

In addition, the same analysis also found that every 50 mg increase in daily vitamin C intake reduced the risk of hip fracture by 5%.

The mechanism behind it is related to vitamin C’s collagen synthesis, scavenging free radicals, regulating osteogenesis and osteoclastic metabolism.

*Conclusion: Higher intake of vitamin C from natural foods can reduce the incidence of hip fractures

17. Vitamin C reduces cancer incidence

Traditionally, vitamin C has been considered a potential cancer chemopreventive factor due to its ability to scavenge free radicals, reduce vitamin E, and reduce DNA oxidative damage.

Several meta-analyses have found that consuming more vitamin C from the natural diet can help reduce the risk and even survival rate of a variety of cancers (including stomach cancer, pancreatic cancer, esophageal cancer, prostate cancer, lung cancer, breast cancer, etc.). Notes 12345

As for intravenous vitamin C therapy for cancer, it was proposed by Nobel laureate Linus Pauling in the 1970s and is still used in natural medicine and integrative therapy (the mechanism behind it is related to the oxidative and anti-inflammatory effects at high concentrations, which can reduce tumor cell growth, proliferation and migration).Note 6

According to a systematic analysis, intravenous vitamin C combined with chemotherapy may help improve treatment outcomes (e.g. time to cancer recurrence, survival, quality of life) and side effects of chemotherapy (including fatigue, nausea, insomnia, constipation and depression), and several cases of cancer remission have been reported.Note 7

However, the authors believe that due to the lack of relevant evidence, more empirical evidence is needed to confirm the safety and efficacy of intravenous vitamin C in the future.

18. Vitamin C reduces the risk of cervical precancer

Cervical cancer ranks third among common cancers in women, after breast cancer and colorectal cancer. According to statistics, there are about 3,50 new cases worldwide every year.

Cervical neoplasia is a type of cervical precancerous lesion, of which grade 3 cervical intraepithelial tumor (CIN), if not properly treated, has a risk of developing cancer within 10 years as high as 4%. Note 2

A meta-analysis (including 12 population studies) showed that vitamin C intake was inversely related to the incidence of cervical neoplasia, especially that every 50 mg increase in daily intake helped reduce the risk of cervical tumor by 8%. Note 1

The mechanism behind it may be related to vitamin C’s antioxidant properties, inhibition of free radicals and reduction of DNA damage, inhibition of matrix metalloproteinases (MMPs), and prevention of cancer cell invasion (although the authors believe that more research is still needed to further verify).

*Conclusion: Population observation shows that higher vitamin C intake can reduce the risk of precancerous lesions of cervical cells

19. Vitamin C reduces the risk of cataracts (Cataract).

Ageing-related cataracts are one of the leading causes of blindness, and millions of people worldwide are associated with the development of cataracts each year.Note 4

Under the threat of an aging population, cataracts are almost inevitable, and about 75% of the elderly over 40 years old have a high incidence, in addition to age, the occurrence of cataracts is also significantly related to oxidative stress, smoking, and nutritional intake

A prospective cohort study of 2054 twins showed that dietary intake of more vitamin C reduced the incidence of nuclear cataracts by 33% (compared to those with minimal intake) and reduced the likelihood of developing cataracts by 33% in the next 10 years (the mechanism behind which is related to reduced oxidative stress on crystals).Note 3

Are there any side effects of vitamin C?

Vitamin C is very safe and has no side effects by mouth at appropriate doses (it is water-soluble and the body will eliminate unwanted amounts), but high doses (greater than 2,000 mg) may cause diarrhea, gas, heartburn, gastrointestinal discomfort, if this happens, reduce the dose.

Safety precautions (13 contraindications for use)

1. Vitamin C diuretic effect, will accelerate the body’s excretion of water, so be sure to take more water when taking

2. Vitamin C will increase iron absorption, so people with genetic diseases such as hemochromatosis should avoid additional supplementation

3. People with thalassemia, sickle cell anemia or G6PD deficiency (fava bean), do not take a lot of vitamin C, which may cause serious side effects

4. Those who have suffered from kidney stones or poor oxalic acid metabolism should limit the amount of additional supplementation, preferably not exceeding the recommended dietary allowance, or not exceeding 250mg per day (excessive dosage may cause kidney stones).Note 10

5. Do not use it in combination with aluminum-containing antacids, because vitamin C will increase the amount of aluminum absorbed by the body (there are potential concerns), it is recommended to distinguish between the two for 2 to 4 hours.

6. Do not use it in combination with estrogens, because vitamin C will reduce the speed of the body’s elimination of estrogen, which may increase the effect and side effects of estrogen

7. Do not use in combination with psychiatric drugs: fluphenazine, because vitamin C will reduce the effect of the drug

8. Do not use in combination with chemotherapy cancer drugs, because vitamin C may reduce the effectiveness of drugs

9. Do not use in combination with HIV/AIDS drugs, such as protease inhibitors, because vitamin C may reduce the effectiveness of drugs, related drug names such as: amprenavir, nelfinavir, ritonavir, saquinavir

10. Do not use in combination with cholesterol-lowering drugs (Statins), because vitamin C may reduce the effectiveness of drugs, related drug names such as: atorvastatin, fluvastatin, lovastatin, pravastatin

11. Do not use in combination with anticoagulant drugs (Warfarin), a large amount of vitamin C may reduce the efficacy of the drug and may cause blood clotting problems

12. Do not use in combination with anti-inflammatory and analgesic drugs, because a large amount of vitamin C may reduce the speed of the body to break down drugs, may increase the occurrence of adverse reactions, related drug names such as: acetaminophen, aspirin, Choline Magnesium Trisalicylate, salicylyl salicylic acid

13. Do not use it in combination with calcium ion blockers (Nicardipine, Nifedipine), because taking it at the same time may reduce the amount of vitamin C absorbed by cells.

Where can I buy the highest quality Vitamin C that is recommended by most people?

Lake Avenue Nutrition, Vitamin C, Quali-C, 1,000 mg, 60 Veggie Capsules

(Direct shipping from the United States / Worldwide delivery)

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Product Features:

Quali-C is currently the world's top vitamin C (from Scotland) of European origin, the raw material is not genetically modified, and it has passed a number of international certifications to ensure the purity of the product and the quality is unmatched

* Quali-C is one of the brands of DSM Nutritional, one of the world's largest health ingredient manufacturers, and one of the first pharmaceutical companies in the world to synthesize vitamin C


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