Vitamin C

Ascorbic acid is the chemical name of vitamin C, a water-soluble, easily oxidizable vitamin. The official name according to IUPAC rules is (R)-5-[(S)-1,2-dihydroxyethyl]-3,4-dihydroxy-5H-furan-2-one. Vitamin C is a hexuronic acid. The pKS value is 4.2, the solubility in water (20°C) is 333 g/l. The molar mass is 176.13 g/mol. The E number of ascorbic acid, as found in food ingredient lists, is E 300. The chemical formula is C6H8O6. The melting point is 190-192 °C. A boiling point cannot be specified as the substance decomposes from the melting point. There are 4 different stereoisomeric forms of ascorbic acid, which have optical activity, as the 4th and 5th carbon atoms are each a center of asymmetry:

• L-ascorbic acid (also 2,3-endiol-L-gluconic acid-γ-lactone, (R)-5-[(S)-1,2-dihydroxyethyl]-3,4-dihydroxy-5H-furan-2-one)
• D-ascorbic acid
• L-isoascorbic acid
• D-isoascorbic acid

The molecules L- and D-ascorbic acid behave like image and mirror image of each other, they are enantiomers, as are L- and D-isoascorbic acid. L-ascorbic acid and D-isoascorbic acid as well as D-ascorbic acid and L-isoascorbic acid are epimers, they differ in the configuration of only one C atom. Vitamin C is the generic name for all compounds that have the same biological effect as L-ascorbic acid. D-ascorbic acid and L-isoascorbic acid are biologically inactive, D-isoascorbic acid has only a low biological activity. Dehydro-L-ascorbic acid belongs to the group of vitamin C compounds, as it is reduced to L-ascorbic acid in the body.

Significance

Vitamin C is a radical scavenger and has an antioxidant effect (reducing agent). It is an important cofactor in the hydroxylation reaction and thus controls the body's own production of collagen. It also plays an important role in the formation of amino acids. Due to its reducing properties, it is also occasionally used as a developing substance in photographic developers and is also used as an antioxidant in food production. Most organisms are able to biosynthesize this vitamin via glucose metabolism. Only humans, guinea pigs, primates and some birds and fish cannot produce the vitamin themselves. The storage capacity of the vitamin is very low in humans, so that this substance must be constantly supplied.

Ascorbic acid is sensitive to light, air, water and heat. However, it is stable against oxygen in fruit juices with a pH value below six. However, vitamin C is not very stable, so considerable losses occur during storage. Blanching and freezing greatly reduces vitamin loss. This is why frozen products often contain more vitamin C than fresh products that have been in the fridge for some time. During prolonged cooking, the water-soluble vitamin is also washed out of the food or inactivated, just as it is during reheating, keeping warm or soaking.

Occurrence

In food, vitamin C is mainly found in fruit, vegetables and green tea, but its content decreases during cooking, drying or soaking. Citrus fruits such as oranges, lemons and grapefruits contain a lot of vitamin C. Kale has the highest vitamin C content of all types of cabbage (105 mg/100 g of edible substance).

Ascorbic acid is bound in cabbage vegetables in the form of ascorbigens A and B. When the vegetables are cooked, the molecules break down into L-ascorbic acid and indole, so that they can contain more vitamin C when cooked than when raw. However, overcooking partially destroys the vitamin. Red cabbage and white cabbage/sauerkraut are also sources of vitamin C (50 mg, 45 mg and 20 mg/100 g respectively). The highest natural vitamin C concentrations have been found in camu camu and acerola cherries. Sea buckthorn also provides vitamin C in high concentrations.

• Pear 5
• Peach 10
• Banana 11
• Cultivated apple 12
• Avocado 13
• Pineapple 20
• Blueberry 22
• Orange (orange) 50
• Lemon 53
• Strawberry 61
• Mountain ash 98
• Kiwi 100
• Blackcurrant 189
• Sea buckthorn berry 450
• Rosehip 1250
• Acerola cherry 1700
• Camu-Camu 2000

Deficiency symptoms (hypovitaminosis)

Albert Szent Györgyi, a Hungarian scientist, identified vitamin C as an effective substance against scurvy in 1933. However, vitamin C is only fully effective in the presence of a flavanol known as vitamin C2. Neither of the two substances alone can cure scurvy, but in combination they are effective even in small quantities.

Only a few vertebrates, including primates, pigs and guinea pigs, are not capable of biosynthesizing ascorbic acid from glucuronic acid; they lack L-gluconolactone oxidase. As the human body cannot produce vitamin C itself, the requirement must be met through food or food supplements. Deficiency symptoms lead to scurvy in the long term. They can occur in the case of malnutrition and deficiencies such as poor diets and alcoholism or increased requirements (pregnancy, smoking).

Only L(+)-ascorbic acid has biological activity. Its strongly acidic character is due to the hydroxyl group on the C3 atom (pKs = 4.2). Deprotonated, it results in a resonance-stabilized anion. The other enolic OH group has no acidic properties (pKs = 11.8). Due to its antioxidant effect, it protects other very important metabolites such as glutathione (cell division control = cancer "protection") from oxidation.

Overdose (hypervitaminosis)

There are no known cases of hypervitaminosis for vitamin C as there are for vitamin A, for example, as the body excretes an excess of ascorbic acid. However, it has been found that it can destroy vitamin B12 in very high doses.

High single doses (5-10 g) can cause temporary insomnia (similar to caffeine) and diarrhea.

Infant scurvy occurs when very large amounts of vitamin C are consumed during pregnancy. Excess ascorbic acid is excreted via the kidneys' own channel proteins. At high concentrations, these are increased, which also occurs in the embryo. After birth, the infant therefore excretes too much vitamin C, which is no longer replaced by the normal amount in the baby food.

Nature reported in 1998 that high doses of vitamin C can cause damage to genetic material.

Task / Function

The name ascorbic acid is derived from the disease scurvy, which can be prevented and cured by ascorbic acid. Together with niacin and vitamin B6, vitamin C regulates the production of L-carnitine, which is needed to burn fat in the muscles. It also promotes the absorption of iron in the small intestine. It is involved in collagen synthesis and the formation of steroid hormones, as well as in the metabolism of phenylalanine, tyrosine, folic acid and iron. Vitamin C is a powerful antioxidant and has a cortisol-lowering effect.

Vitamin C is also used to treat colds. However, a meta-analysis of 55 studies shows that, contrary to popular belief, vitamin C cannot prevent colds. At best, vitamin C appears to have a slight preventative effect in people who - like some extreme athletes - are exposed to heavy physical exertion or extreme cold. However, there are indications that the duration of a cold can be slightly reduced by the vitamin (R. Douglas & H. Hemilä: PLoS Medicine, vol. 2, no. 6, p. e168, 2005).

Vitamin C is easily destroyed by storage and cooking. In cabbage and kale, the vitamin is stored in a precursor (ascorbigen), the formation of which is favored by cooking.

Potential health benefits of vitamin C supplementation

Vitamin C could reduce the risk of chronic diseases

Vitamin C is a powerful antioxidant that can strengthen the body's natural defenses (1). Antioxidants are molecules that can promote and improve the function of the immune system. They do this by protecting the body's cells from harmful molecules called free radicals.

When free radicals accumulate in the body, they can promote a condition known as oxidative stress, which has been linked to many chronic diseases (2). Studies have shown that consuming more vitamin C can increase the body's antioxidant levels by up to 30%. This helps the body's natural defenses to fight inflammation (3, 4).

Summary: Vitamin C is a powerful antioxidant that can increase the body's antioxidant levels, helping to reduce the risk of chronic diseases such as heart disease.

Vitamin C could help control high blood pressure

Around a third of the population of the western world suffers from high blood pressure. High blood pressure increases the risk of heart disease, which is the leading cause of death worldwide. Studies have shown that vitamin C can help lower blood pressure in people suffering from hypertension.

One study conducted in animals found that taking a vitamin C supplement helped relax the blood vessels that carry blood away from the heart, which helped lower blood pressure (5).

A meta-analysis of 29 human studies found that taking a vitamin C supplement in healthy adults could lower systolic blood pressure (the upper value) by an average of 3.8 mmHg and diastolic blood pressure (the lower value) by an average of 1.5 mmHg.

In adults with high blood pressure, vitamin C was able to reduce systolic blood pressure by an average of 4.9 mmHg and diastolic blood pressure by an average of 1.7 mmHg (6). However, while these results are promising, the long-term effects of vitamin C on blood pressure are not yet known.

Summary: Scientific research has found that vitamin C can lower blood pressure in both healthy people and people with high blood pressure.

Vitamin C could reduce the risk of heart disease

Heart disease is the leading cause of death worldwide. Many factors, including high blood pressure, high blood triglyceride levels, high levels of "bad" LDL cholesterol and low levels of good HDL cholesterol, can increase the risk of heart disease. Vitamin C may help to reduce these risk factors, which may lead to a lower risk of heart disease.

A meta-analysis of 9 studies with a total of 293,172 participants concluded that after 10 years, those who took at least 700 mg of vitamin C daily had a 25% lower risk of heart disease compared to those who did not use a vitamin C supplement (7).

Interestingly, another analysis of 15 studies found that consumption of vitamin C in the form of food - rather than supplements - was associated with a lower risk of heart disease.

However, the scientists were not sure whether the people who ate foods rich in vitamin C also followed a healthier lifestyle than those who used a supplement. It therefore remains unclear whether the observed difference was attributable to vitamin or other aspects of the diet (8).

Another analysis of 13 studies looked at the effects of taking at least 500 mg of vitamin C per day on risk factors for heart disease such as blood cholesterol levels and triglyceride levels. This analysis found that taking a vitamin C supplement significantly reduced bad LDL cholesterol levels by 7.9 mg/dl and blood triglyceride levels by 20.1 mg/dl (9).

In short, taking at least 500 mg of vitamin C appears to reduce the risk of heart disease. However, if you are already following a diet rich in vitamin C, then additional vitamin C supplements are unlikely to provide any additional heart health benefits.

Summary: Vitamin C supplements are associated with a lower risk of heart disease. They may reduce risk factors for heart disease including LDL cholesterol levels and triglyceride levels.

Vitamin C may reduce uric acid levels in the blood and help prevent gout attacks

Gout is a type of arthritis that affects around 4% of adults in the western world (10). Gout is extremely painful and involves inflammation of the joints - particularly the joints of the big toe. People who suffer from gout experience swelling and sudden, severe attacks of pain (11).

Gout symptoms occur when there is too much uric acid in the blood. Uric acid is a waste product produced by the body itself. At high levels, uric acid can crystallize and build up in the joints.

Interestingly, several studies have shown that vitamin C could help to reduce uric acid levels in the blood and thus protect against gout attacks. For example, a study of 1,387 men showed that those who consumed the most vitamin C had significantly lower uric acid blood levels than those who consumed the least vitamin C (12).

Another study followed 46,994 healthy men over a 20-year period to determine whether vitamin C intake was associated with the development of gout. This study found that people who took a vitamin C supplement had a 44% lower risk of gout (13).

Additionally, an analysis of 13 studies found that taking a vitamin C supplement for 30 days significantly reduced uric acid levels in the blood compared to a placebo (14).

However, although there appears to be a strong association between vitamin C intake and uric acid levels, further studies are needed to further investigate the effects of vitamin C on gout.

Summary: Vitamin C-rich foods are associated with reduced blood uric acid levels and a lower risk of gout.

Vitamin C helps prevent iron deficiency

Iron is an important nutrient that has a variety of functions in the body. It is essential for the production of red blood cells and the transportation of oxygen throughout the body. Vitamin C supplements can help to improve the absorption of iron from food. Vitamin C supports the conversion of certain types of iron, such as plant-based iron compounds that are poorly absorbed by the body, into forms of iron that are more easily absorbed (15). This is particularly useful for people on a meat-free diet, as meat is one of the primary sources of dietary iron.

In fact, consuming 100 mg of vitamin C can improve iron absorption by 67% (16). As a result, vitamin C may help reduce the risk of anemia in people who are susceptible to iron deficiency.

In one study, 65 children with mild iron deficiency anemia were given a vitamin C supplement. The researchers found that the vitamin C supplement alone helped control the anemia in these children (17).

If you suffer from low iron levels, eating more vitamin C-rich foods or taking a vitamin C supplement could help improve iron blood levels.

Summary: Vitamin C can increase the absorption of poorly absorbable iron such as iron from plant sources and reduce the risk of iron deficiency.

Vitamin C can improve the function of the immune system

One of the main reasons many people take vitamin C supplements is to improve immune function, as vitamin C is involved in many aspects of the immune system. First of all, vitamin C helps stimulate the production of white blood cells, also known as lymphocytes and phagocytes, which help protect the body from infection (18).

Secondly, vitamin C helps these white blood cells to function more effectively while protecting them from potentially harmful molecules such as free radicals. Third, vitamin C is an essential part of the skin's defense system. It is actively transported to the skin where it can act as an antioxidant and help to strengthen the skin barrier (19). Furthermore, studies have shown that vitamin C can accelerate wound healing (20, 21).

In addition, low vitamin C levels are associated with more severe disease progression. For example, it has been shown that people suffering from pneumonia have lower vitamin C levels and that vitamin C supplements can accelerate healing (22, 23).

Summary: Vitamin C improves the function of the immune system by helping white blood cells function more effectively, by strengthening the skin's defense system and by helping wounds heal faster.

Vitamin C can protect memory and thinking skills as we age

Dementia is a broad term used to describe symptoms of poor thinking and memory. It affects over 35 million people and typically occurs in older adults. Studies suggest that oxidative stress and inflammation around the brain, spinal cord and nerves can increase the risk of dementia (24). Vitamin C is a powerful antioxidant. Low levels of this vitamin are associated with impaired thinking ability and poorer memory performance (25, 26).

In addition, several studies have shown that people suffering from dementia have lower blood levels of vitamin C (27, 28). Furthermore, it has been shown that a higher vitamin C intake in the form of food or supplements during ageing has a protective effect on thinking ability and memory (29, 30, 31).

Vitamin C supplements could help against conditions such as dementia if people do not get enough vitamin C from their diet. However, more human studies are needed to fully understand the effects of vitamin C on nervous system health (32).

Summary: Low vitamin C levels are associated with an increased risk of cognitive and memory disorders such as dementia, while it has also been shown that high vitamin C intake from food and supplements may have a protective effect.

Vitamin C and cancer

Vitamin C is produced by most living organisms. Exceptions are humans, monkeys, guinea pigs and some fish and bird species. According to current knowledge, vitamin C prevents the degeneration of healthy cells into cancer cells and their spread. Some studies even show a reversal of the degeneration process to healthy cells. Vitamin C appears to have a direct effect on cancer-causing substances by inactivating them, or it protects the sensitive DNA of the cell nucleus. Deficiency symptoms lead to a weakening of the connective tissue. In addition to an intact immune system, strong connective tissue is also required to inhibit tumors. This makes penetration into the blood vessels and thus metastasis more difficult.

Vitamin C strengthens both the cellular immune defense by activating the lymphocytes and macrophages and the hormonal defense by increasing the serum concentrations of immunoglobulins. Some studies show a consistent link between low plasma levels of vitamin C and an increased incidence of certain types of cancer. A good supply of vitamin C therefore presumably contributes to a lower incidence of certain types of tumor.

The chemist Linus Pauling was of the opinion that high doses of vitamin C not only prevent cancer, but can even cure it under certain circumstances. However, the Linus Pauling Institute of Science and Medicine, which he founded, has since abandoned the massive doses of vitamin C.

The connection between the (under)supply of vitamin C and the development of cancer has not yet been clearly established in medicine.

Additive in food production

Ascorbic acid is added to many food products as an antioxidant or reddening agent under the number E 300. Ascorbic acid is added to flours to increase the gas holding capacity and volume of the dough. This can be explained by the formation of additional disulphide bridges between the gluten strands of the dough.

Demand

In large parts of the world, the supply of vitamin C is generally good; according to the recommendation of the German Nutrition Society, the daily requirement of an adult is 100 mg. However, much higher amounts (up to 5000 mg) are also considered safe. Excess amounts are excreted by the body via the urine.

Requirements in sport

The requirement of competitive athletes is higher - simply due to greater losses through sweat. My recommendation is to take 1000-5000mg a day several times a day with meals. Based on empirical data, especially based on positive reports from many athletes, such high dosages can be recommended, especially for athletes who train hard. Athletes experience less susceptibility to infections, better regeneration and faster healing of injuries when vitamin C is taken in the gram range. Vitamin C is best taken 1g in the morning, before and after training and before going to bed, especially in weight training.

References:

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