Last updated by Dr Sarah Brewer on
Vitamin C benefits are due to its powerful antioxidant action and its ability to reduce tiredness and fatigue, boost collagen production in the skin, and protect against viral infections during times of physical and emotional stress.
- What is vitamin C?
- Vitamin C benefits
- Food Sources of vitamin C
- Vitamin C deficiency
- Vitamin C and wrinkles
- Vitamin C and colds
- Vitamin C and diabetes
- Vitamin C and heart disease
- Vitamin C and cataracts
- Vitamin C and gallstones
- Vitamin C and gout
- Vitamin C and osteoporosis
- Vitamin C and osteoarthritis
- Vitamin C and male fertility
- Vitamin C dose
- Vitamin C Supplements
- Vitamin C Safety
What is vitamin C?
Vitamin C (ascorbic acid) is a water-soluble vitamin whose chemical structure is closely related to glucose. Most animals can synthesise all the vitamin C they need from glucose and galactose sugars, but we humans lack the enzyme (l-gulonolactone oxidase) needed for this conversion.
The goat, for example, which weighs around the same as an adult man, produces between 2g and 13 g of vitamin C per day depending on its levels of stress and illness. The more it is stressed, the more vitamin C it makes.
The only animals who are unable to synthesise their own supplies of vitamin C are:
- Guinea pigs
- The Indian fruit bat
- The Red-vented bulbul (an Asian songbird)
- Rainbow trout
- Coho salmon
- A single strain of Japanese laboratory rat.
Why our ancestors lost, or never acquired, the ability to synthesize vitamin C is one of the greatest mysteries of human biochemistry. It is thought to have resulted from a genetic accident occurring around 60 million years ago which, according to some scientists, mean we all suffer from a genetic disease, with the tongue-twister name of hypoascorbemia.
Because our primitive ancestors ate a vegetarian diet full of vitamin C-rich plants such as purslane, their vitamin C intake was higher than in the modern diet at an estimated 392 mg a day, allowing them to survive despite this genetic defect. In modern times, our dietary vitamin C intake has plummeted, and our inability to make vitamin C has been blamed for increasing our risk of a number of common illnesses such as viral infections, raised cholesterol levels, coronary heart disease and cancer as well as reducing our ability to cope with stress.
Vitamin C benefits
Vitamin C is an important antioxidant in watery parts of the body, especially the circulation and the eye lens. Vitamin C also regenerates other antioxidants, including vitamin E, and is needed for at least 300 metabolic reactions to work normally.
Vitamin C is essential for conversion of the amino acid, proline, to hydroxyproline during collagen synthesis and is also involved in the metabolism of stress hormones and the regulation of immune reactions.
Within the EU, the European Food Safety Authority has authorised health claims that vitamin C contributes to:
- The normal function of the immune system during and after intense physical exercise
- Normal collagen formation for the normal function of blood vessels, bones, cartilage, gums, skin and teeth
- Normal energy-yielding metabolism
- Normal functioning of the nervous system
- Normal psychological function
- Normal function of the immune system
- The protection of cells from oxidative stress
- The reduction of tiredness and fatigue
- The regeneration of the reduced form of vitamin E
- Increased iron absorption.
Food Sources of vitamin C
Vitamin C is mainly found in fruit and vegetables, especially:
- kiwi fruit
- citrus fruit
- capsicum peppers
- green leafy vegetables.
Animal sources of vitamin C include kidney, liver and whale skin, which is an important source within the Inuit diet.
Vitamin C is one of the most unstable micronutrients, however, and up to two-thirds is lost during food processing, cooking and storage. Fruit juices rapidly lose their vitamin C content when exposed to air, even if chilled. A carton of opened orange juice left in the fridge for a week will contain little vitamin C.
Vitamin C deficiency
Lack of vitamin C causes scurvy, a deficiency disease associated with poor collagen production, poor wound healing, bleeding skin and gums and loss of teeth. If untreated, scurvy is fatal.
A minimum daily intake of 10mg vitamin C is needed to prevent scurvy, although 20 mg per day is needed for proper wound healing.
Symptoms that may be due to vitamin C deficiency include:
- frequent colds and other infections
- dry, rough, scaly skin
- broken thread veins around hair follicles
- dry, fissured lips
- muscle and joint pain
Symptoms that may be due to major vitamin C deficiency are:
- poor wound healing
- easy bruising
- misshapen, tangled, brittle, ‘corkscrew’ hair
- hair loss
- inflamed, swollen, bleeding gums,
- loose teeth
- bleeding skin, eyes and nose
Vitamin C and wrinkles
Women’s skin ages 25% faster than that of men between the ages of 40 and 50, due to the hormonal changes occurring around the menopause. When levels of oestrogen fall after the menopause, the production of collagen and elastin fibres slow and those present become increasingly matted and tangled so skin loses its resilience and elasticity. Vitamin C helps to overcome this by promoting collagen production, and protecting against the ageing effects of ultraviolet light.
Ultraviolet light damages skin and long-term sun exposure causes photo-ageing with skin becoming increasingly thickened, yellow, scaly, mottled and wrinkled with a coarse, leathery texture. Vitamin C protects skin during UV exposure to reduce sunburn and is now added to many cosmetic creams designed to slow the visible signs of skin ageing.
Researchers have found that women over the age of 40 with the highest dietary intakes of vitamin C have less skin wrinkles and dryness than those with low intakes. An American study involving over 4000 women, aged 40 – 70 years found that a high vitamin C intake reduced the appearance of wrinkles by 11%.
Vitamin C serums are among the most popular and effective anti-ageing preparations to reduce facial ageing.
Vitamin C and colds
Vitamin C suppresses the activation of viral genes so that viruses cannot survive in cells with high vitamin C levels. High dose vitamin C (ascorbic acid) has been used medically to treat persistent viral infections and can produce dramatic results.
Whether or not vitamin C can prevent or treat the common cold is more controversial, although its proven antiviral action and it anti-inflammatory effects should make it a highly effective treatment on paper.
Studies involving school children and students suggest that vitamin C can reduce the risk of catching a cold by as much as 30%. Heavy physical exercise increases the likelihood of respiratory infections, and vitamin C supplements can protect military troops and endurance athletes in training by reducing the risk of developing cold symptoms by half, at doses of 600mg to 1g vitamin C per day.
The results from 29 trials involving 11,300 people also show a consistent ability of vitamin C supplements to reduce the duration of a cold by 8% in adults and by 14% for children at doses of between 1g and 2g per day. The severity of cold symptoms was also reduced.
In people with asthma, developing a cold is a common trigger for an asthma attack. At least two studies show that taking vitamin C supplements can decrease the occurrence of asthma associated with respiratory infections by as much as 78% – partly through the antiviral action, but also through an ability to reduce airway sensitivity
It therefore seems that vitamin C is most effective at boosting immunity against the common cold in people who are experiencing physical or emotional stress – times when, like the goat, we should be ramping up our own natural production of vitamin C if it weren’t for that pesky genetic mutation way back in the dawn of human history.
Vitamin C and diabetes
Vitamin C has beneficial effects on glucose control, yet people with diabetes have circulating levels of vitamin C that are around 30% lower than in people without diabetes, as requirements are increased to help offset the metabolic abnormalities associated with diabetes.
When blood glucose levels are raised, some glucose is converted to sorbitol inside cells which contributes to diabetes complications affecting the eyes (retinopathy, cataracts) and nervous system (peripheral neuropathy). Vitamin C reduces sorbitol formation by blocking an enzyme (aldose reductase) needed to convert glucose to sorbitol.
Taking 1g vitamin C (ascorbic acid) per day for just 2 weeks can reduce the amount of sorbitol within red blood cells by over 12%. Taking 2g vitamin C daily reduces the build-up of sorbitol in red blood cells by 44.5% in people with diabetes.
Vitamin C and heart disease
Vitamin C protects cholesterol in the blood stream from oxidation to help protect against heart attack and stroke. Vitamin C also improves the liver’s ability to convert cholesterol into bile acids.
A study in Norfolk, UK, involving over 20,000 adults found that those with the highest blood levels of vitamin C from fruit and vegetables were 22% less likely to have high blood pressure than those with low levels. Those with good vitamin C intakes were also half as likely to die from any medical cause, including cardiovascular disease, during the follow-up period of four years.
Vitamin C and cataracts
Vitamin C is an important antioxidant in the eye, and the level of vitamin C in the lens is 60 times that found in the circulation. Several studies suggest that long-term consumption of vitamin C supplements might reduce the development of age-related cataracts.
The results from 30 trials, involving around 18,000 people, concluded that those with the highest vitamin C intakes were 19% less likely to develop cataracts than those with the lowest intakes. When blood levels of vitamin C were measured, those with the highest circulating levels were 30% less likely to develop cataracts than those with the lowest levels. The researchers concluded that good vitamin C intakes should be encouraged for the primary prevention of cataract.
Vitamin C and gallstones
Vitamin C (ascorbic acid) affects the breakdown of cholesterol to bile acids and, in women, may reduce the risk of gallstone symptoms by 13%. A similar relationship was not found for men, however. This is probably because women have a greater risk of gallstones due to hormone changes that affect gallstone formation, especially those occurring during pregnancy.
Vitamin C and gout
Vitamin C can lower uric acid levels to protect against gout. The results from 13 trials, involving 556 people with recurrent gout showed that taking 500mg vitamin C per day significantly reduces serum uric acid levels.
Research involving almost 47,000 males whose vitamin C levels were checked every 4 years for 20 years also found a protecive effect against gout. Compared with men who had vitamin C intakes of less than 250mg per day, those with intakes of 500mg – 999mg per day were 17% less likely to develop gout; those with intakes of 1000 – 1499 mg per day were 34% less likely to develop gout, and those with intakes of 1500mg per day or more were 45% less likely to experience gout.
Vitamin C and osteoporosis
Vitamin C is essential for the synthesis of collagen, a structural protein that makes up 30% of bone volume. Vitamin C stimulates bone-building cells (osteoblasts), enhances vitamin D activity and boosts calcium deposition in bone. In women after the menopause, those with osteoporosis have significantly lower dietary vitamin C intakes than those without osteoporosis.
Vitamin C and osteoarthritis
Vitamin C may reduce the risk of cartilage loss and disease progression in people with osteoarthritis. The risk of having osteoarthritis, for example, is 1.9 times reduced in people who obtain recommended intakes of vitamin C, or higher, than those with lower intakes. Vitamin C supplement may help to reduce arthritis knee pain in particular.
Vitamin C and male fertility
Vitamin C is found in semen at concentrations eight times higher than in the circulation. Vitamin C is vital for sperm health in stopping sperm from clumping together and in protecting the genetic material (DNA) of sperm against oxidative damage.
Taking 1g vitamin C twice a day for 2 months has been shown to increase average sperm count from 14.3 x106 per ml to 32.8 x 106 per ml; the number of sperm with normal morphology from 43% to 66.7% and the number of sperm with normal motility from 31.2% to 60.1%.
Vitamin C dose
Requirements increase during pregnancy and lactation.
It has also been suggested that smokers should consume an additional 35 mg vitamin C per day than non-smokers to help offset the increased oxidative damage caused by exposure to cigarette smoke.
The average Western diet supplies 64 mg vitamin C per day.
These doses are very much minimums designed to prevent symptoms of scurvy. Many experts believe that optimal doses are considerably higher for immune, anti-ageing and anti-inflammatory benefits.
Supplements that provide vitamin C doses of 500mg and 1000mg (1 gram) are among the most popular doses for every day use.
Vitamin C Supplements
The efficiency of vitamin C absorption depends on the amount consumed. At intakes of up to 200 mg as a single dose, absorption of vitamin C is almost complete through an active transport process.
At single doses of over 500 mg, vitamin C is also absorbed through a process of diffusion which is less efficient so that only around half of a 1.5g dose is absorbed, and only 16% of a massive 12g dose.
Large doses of vitamin C may trigger indigestion or diarrhoea. This is largely due to the acidity of vitamin C rather than a specific sign of toxicity. Some people are more sensitive to the acidity of vitamin C than others.
If vitamin C supplements cause indigestion, try a non-acidic form called Ester C. This contains a mixture of the active break-down products of vitamin C (eg threonate) which have a neutral pH, the same as distilled water, that do not trigger indigestion.
Ester C is sometimes described as ‘body-ready’ as it has the additional benefits of entering the blood stream more quickly than normal vitamin C, produces higher vitamin C levels inside cells, and stays in the body for longer.
Another non-acidic bioavailable form of vitamin C is called liposomal vitamin C. This is a super absorbent liposomal gel which is stirred into water to drink.
Vitamin C Safety
Some vitamin C is metabolised to oxalic acid, but claims that large doses could trigger oxalate kidney stones have proved unfounded. However, recurrent stone formers who have a defect in ascorbic acid or oxalate metabolism, and people with renal failure are usually advised to restrict their daily vitamin C intake – for example, to no more than 100 mg.
People with an iron-storage disease, haemochromatosis, should not take vitamin C supplements except under medical advice.
Suddenly stopping high-dose vitamin C supplements can cause temporary symptoms of deficiency (rebound scurvy) when enzymes activated by high levels of vitamin C are suddenly deprived of the extra vitamin C they need to work properly.
The European Food Safety Authority has determined a tolerable upper intake for long-term use from vitamin C supplements as 1gram daily.
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