Comprehensive Guide To Vitamin C

Updated: Oct 19, 2020

During COVID-19 and flu season, it is vital to consume adequate amounts of vitamin C to fortify your immune system and help protect against foreign infections. So, it's important to know just what vitamin C is and what it does within your body. In this comprehensive guide to vitamin C, you will learn everything you need to know about ascorbic acid.

What is Vitamin C

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin that cannot be stored within the body, therefore daily intake is required. Vitamin C is an essential antioxidant and is needed for over 300 metabolic reactions within the body, including the production of collagen (a major structural protein in the body). It is vital for the growth and repair of the skin, bones, teeth and reproduction. Vitamin C is also involved in the metabolism of stress hormones, evidence suggests that vitamin C acts as an antihistamine and may reduce the effects of allergic reactions. It also has anti-bacterial and anti-viral properties that are used to treat or prevent common colds and are extremely effective at eradicating influenza. (1) (2)

The most important role of vitamin C is being an antioxidant. It is also vital for regenerating other antioxidants, such as vitamin E. Studies have found that men and women with high dietary intake of vitamin C have a lower risk of developing coronary heart disease and stroke. Ascorbic acid protects genetic material from oxidative damage and mutation, it may also reduce the risk of developing cancer.

Another role of vitamin C is its ability to increase the absorption of iron. When taking iron tablets, they should ideally be washed down with fresh orange juice.

The majority of animals can synthesize their own vitamin C, but humans and primates lack the enzyme (L-gluconolactone oxidase) needed to create it. A goat can synthesize between 2 and 13 grams of vitamin C each day, which dramatically increases during times of physical stress or illness.

The reason why humans lack the enzyme required to synthesize vitamin C is unknown. It is thought to have resulted from a genetic evolution millions of years ago. Scientists have suggested that we all suffer from a genetic disease called hypoascorbaemia, which results in scurvy. This genetic disease increases the risk of several common illnesses such as viral infections, raised cholesterol levels, coronary heart disease and cancer, as well as reducing our ability to cope with stress.

Our primitive ancestors were mostly vegetarian and therefore had a diet full of vitamin C-rich plants. Their dietary intake of vitamin C per day was much higher than ours and is estimated that they consumed 392mg of vitamin C per day. This high vitamin C intake is why our ancestors were able to survive while lacking the ability to synthesize vitamin C endogenously.

Vitamin C's chemical makeup comprises carbon, hydrogen, and oxygen. In its purest form, it is a white solid and is formed synthetically from the sugar dextrose. Therefore it can be used as a vitamin and as a food preservative.

History of Vitamin C

Centuries ago, an unknown disease wreaked havoc across sailors. The early symptoms of this disease were fatigue, joint pain, swelling in the limbs and easily bruised skin. As it progressed, the sailors' gums bled, their teeth fell out and haemorrhaging often resulted in death.

"It rotted all my gums, which gave out black and putrid blood. My thighs and lower legs were black and gangrenous, and I was forced to use my knife each day to cut into the flesh in order to release this black and foul blood. I also used my knife on my gums, which were livid and growing over my teeth. . . . When I had cut away this dead flesh and caused much black blood to flow, I rinsed my mouth and teeth with my urine, rubbing them very hard. . . . And the unfortunate thing was that I could not eat, desiring more to swallow than to chew. . . . Many of our people died of it every day and we saw bodies thrown into the sea constantly, three or four at a time." - Quote from a scurvy survivor

James Lind, a Scottish doctor in 1747, is remembered as the person who found the “cure” to scurvy by suggesting that fresh citrus fruits, more specifically lemons, were able to prevent and treat scurvy. Due to fresh citrus fruits high vitamin C content, they were able to cure the symptoms of scurvy. It was not until 42 years later however that the Admiralty issued the distribution lemon juice to sailors. The Admiralty tried a cheaper citrus fruit, limes, to cut costs. Lime contains about half the amount of vitamin C than lemons, as such, it was less effective in treating and preventing scurvy.

In 1769, a young British physician, William Stark, took it upon himself to experiment on diet and nutrition, using himself as the subject. After one month of consuming only bread and water, Stark added other foods to his diet, including olive oil, figs, goose meat and milk. Sixty days later he reported his gums were red and swollen, which bled to the touch. A symptom of scurvy. After eight months of self-experimentation, he died on February 23, 1770.

It wasn’t until the 1930’s when a Hungarian man named Albert Szent-Györgyi, along with a colleague, J. L. Svirbely conducted an experiment on guinea pigs, which, like humans, cannot synthesize vitamin C, therefore they must ingest it. The guinea pigs were split into two groups: the first group received boiled food (high temperatures destroys vitamin C) and the second group received food enriched with vitamin C (known as hexuronic acid at the time). The former group suffered from scurvy-like symptoms and died. The latter group, however, flourished. Svirbely and Szent-Györgyi renamed hexuronic acid to vitamin C.

Albert Szent-Györgyi

Benefits of Vitamin C


When blood glucose levels are elevated, some glucose is converted into a substance called sorbitol. The sorbitol that builds up within cells contributes to further symptoms from diabetes, especially those affecting the eyes and nervous system. Vitamin C reduces the formation of sorbitol by blocking an enzyme, aldose reductase, which is needed to convert glucose into sorbitol.

Taking 1g of vitamin C each day for 2 weeks can reduce sorbitol build-up by over 12%. Furthermore, taking 2g of vitamin C daily reduces the build-up of sorbitol by up to 45% in people with diabetes. Smaller doses of vitamin C daily (100mg to 600mg) can normalize sorbitol levels in people with diabetes within 30 days.

Vitamin C has also been shown to improve blood vessel dilation and blood flow in people with diabetes. This is important because blood flow is often impaired in people with diabetes - perhaps due to free-radical damage and the inactivation of the mechanism that dilates blood vessels. The mechanism involves nitric oxide, vitamin C may act in a similar manner.

Glucose Control

In a study involving 40 participants with Type 2 diabetes and raised cholesterol level, taking 1 gram of vitamin C daily for 4 months significantly improved glucose tolerance, lowered total and LDL-cholesterol levels and decreased free-radical damage. The increase in vitamin C in the blood was directly related to the decrease in LDL-cholesterol and the study 'observers' concluded that vitamin C has a vital role in the management and control of Type 2 diabetes.


As vitamin C is an antioxidant, it protects cholesterol in the bloodstream from oxidation. Oxidized cholesterol is linked with hardening and furring up of the arteries (atherosclerosis). Vitamin C has the potential to protect against heart attack and possibly stroke. Taking 500mg each day for 12 months has been shown to significantly lower cholesterol and triglyceride levels. It is thought that vitamin C improves the livers' ability to flush cholesterol from the body through conversion into bile acids.

Cardiovascular Disease

Lack of vitamin C is known as a risk factor for developing a heart attack or stroke. A study involving over 6,600 men and women showed that those with the highest vitamin C levels benefited from a 27% lower risk of coronary heart disease and 26% lower risk of stroke compared to those with low levels of vitamin C. Ascorbic acid may also play a role in preventing symptoms in those with existing coronary heart disease.

A study involving over 19,000 adults aged 45-79 years found that vitamin C content in the body was inversely related to death from all causes of coronary heart disease. Recent findings suggest vitamin C is linked with fibrinogen - a protein that increases the chance of blood clots. The trial observers concluded that even small amounts of vitamin C may have a measurable impact on the risk of developing a fatal heart attack.


Vitamin C is a vital antioxidant for the eyes, the vitamin C content within the eye lens is 60 times higher than the amount in the blood. In a study, those taken 300mg of vitamin C per day had a 70% reduced risk of developing cataracts than those not taking supplements.

The Nurses Health Study found that 60% of early cataracts occurred in women who had not taken vitamin C supplements. Those who had taken vitamin C for at least 10 years had a 45% reduced risk of developing cataracts than those who did not take supplements. These studies suggest that long-term consumption of vitamin C supplements may significantly reduce the risk of developing age-related cataracts.


A meta-analysis of data from 3 trials involving over 2,300 people found an 80% or higher reduction of pneumonia in military recruits and boys. Evidence has suggested vitamin C may be a beneficial treatment in those with developing pneumonia symptoms.

Common Cold

Vitamin C is one of the most popular treatments for the common cold. Ascorbic acid has an anti-viral property that suppresses the activation of viral infections. The common cold virus cannot survive in cells that have a high amount of vitamin C in them, making symptoms less likely to develop.

Studies on students have shown that vitamin C can reduce the risk of developing a cold by as much as 30%. Vitamin C supplements can provide protection to those who are susceptible to respiratory infections. It is believed to have an anti-inflammatory effect in dampening the inflammatory effects produced by viral infections, therefore vitamin C helps suppress symptoms and speed up recovery.

Some research bodies have found that vitamin C at a dose of 1-6 grams daily reduced the duration of a cold by upwards of 20%.


Some studies suggest that those with the highest intake of vitamin C are the least likely to develop certain cancers such as breast, cervical, colorectal, esophageal, lung, pancreatic, prostate, salivary gland, stomach, leukemia, and lymphoma. However, a meta-analysis from over 30 other studies found that vitamin C does not prevent or benefit survival rate.

Macular Degeneration

A recent study found that a high intake of antioxidants, including vitamin C, reduces the risk of age-related macular degeneration by up to 35% in adults over 55 years of age. Age-related degeneration is the leading cause of permanent blindness in people over 60.


Vitamin C affects the breakdown of cholesterol to bile acids, which in women with a good vitamin C intake may reduce the risk of symptomatic gallstones. This is not true for men, however.


A study on nearly 47,000 men found that those with less than 250mg intake of vitamin C were 17% more likely to develop gout than the men taking 500mg to 1g per day. Furthermore, the men with intakes of 1g to 1.5g of vitamin C per day were 34% less likely to develop gout, and those with over 1.5g were 45% less likely to develop it.


High vitamin C intake is associated with improved lung function, and, shockingly, low vitamin C intake seems to be just as harmful to the lungs as smoking cigarettes for 5 years! Some studies suggest taking vitamin C supplements for 2 weeks can reduce the risk of an asthma attack by 25%, compared to those taking a placebo.

As a result, it can lower the needed amount of corticosteroid to controls asthma symptoms. Vitamin C may protect against exercise-induced asthma when taken 30 minutes prior. However, there is insufficient evidence to conclude vitamin C is a viable treatment for asthma.


Ascorbic acid is an essential component for the production of collagen, a major structural protein building block that makes up 30% of the bone density. Vitamin C is extremely important for the healthy growth and repair of tissues and bone. Vitamin C also stimulates the bone-building cells (osteoblasts), enhances vitamin D absorption and boosts calcium absorption in the gut.


Vitamin C may reduce the risk of cartilage loss and progression of the disease in people with osteoarthritis, the most common form of arthritis in the UK. Those with high intakes of vitamin C benefit from a 70% reduced risk of cartilage loss and the development of knee pain. For those that already have osteoarthritis in the knee, vitamin C provides a threefold reduction in the progression of the disease.

Hay Fever

Vitamin C has antihistamine properties, and in one small study, it was found to reduce the bronchial sensitivity to inhaled histamine at a 2g dose. There is some evidence that suggests vitamin C may help reduce the symptoms linked with pollen allergy, but more research is required.

Skin Damage

When ultraviolet light such as the light used in sunbeds, come into contact with the skin, it generates a free-radical called which inhibits an inflammatory reaction known as heliodermatitis.

The ultraviolet light used in sunbeds, for example, are at a much greater intensity than the sun, increasing the risk of skin damage. UV light damages the structure of the skin and interferes with normal cell division.

As a result, this 'photo-ages' the skin and stops the skin cells from regenerating, and collagen fibers - which make up 70% of the skin, become matted and twisted. While sun damage is less severe than UV lights from sunbeds, over a long period of time, it can cause the skin to become dry, inelastic, thick, yellow, scaly, mottled, and wrinkled with a rough texture.

Skin exposed to UV radiation also increases the risk of skin cancer. However, vitamin C protects the skin during UV exposure and reduces the effect of sunburn when taken at a dose of 2g per day (complimented with 1,000IU of vitamin E). However, vitamin C is not a sunscreen, it does not absorb UV light.

It is thought to help by neutralizing free radicals produced by the Ultra-Violet light, as well as being vital for the production of new collagen. Vitamin C, along with vitamin E, is used in many skincare products to reduce the signs of skin aging.


Alzheimer's disease can result from the oxidation of fatty acids (lipoproteins) in the brain which causes the brain cells to die. As vitamin C is an antioxidant, it reduces the free radical damage to the brain cells and may help to reduce the risk of developing senile dementia, including Alzheimer's.

In a study assessing the vitamin C intake of over 1,000 elderly individuals, those taking supplements were associated with a reduced risk of severe cognitive impairment. This means vitamin C can protect against the development of dementia.

Vitamin C Deficiency

Mild deficiency of vitamin C is associated with non-specific symptoms, sometimes called 'pre-scurvy syndrome', which may sometimes include symptoms such as frequent colds and other infections, lack of energy, weakness, and pain in the muscles and joints.

A severe deficiency of vitamin C leads to scurvy. At least 10mg of vitamin C daily is crucial to prevent the development of scurvy. Extreme deficiency symptoms include:

• Slow wound healing

• Dry, scaly skin

• Easy bruising of the skin

• Dry scalp

• Brittle hair

• Hair loss

• Dry, cracked lips

• Inflamed, bleeding gums and tooth loss

• Bleeding skin, eyes, and nose

• Weakness

Vitamin C Dosage

Individuals who smoke require 35mg more vitamin C per day than those who do not smoke.


0-6 months: 40mg

7-12 months: 50mg

1-3 years: 15mg

4-8 years: 25mg

9-13 years: 45mg


14-18 years: 75mg

19+ years: 90mg


14-18 years: 65mg

14-18 years & pregnant: 80mg

14-18 years & breastfeeding: 115mg

19+ years: 75mg

19+ years & pregnant: 85mg

19+ years & breastfeeding: 120mg

Vitamin C Overdose

High doses of vitamin C can cause indigestion and have a laxative effect. Vitamin C is acidic and therefore when it enters the alkaline lower digestive tract, it can cause Acid Rejection Syndrome, which can trigger inflammation, flatulence, diarrhoea, and discomfort. This also reduces the absorption of vitamin C. This can be overcome by taking slow-release vitamin C tablets.

It is important that if you are taking a very high dose of vitamin C and need to reduce the dose, do so very slowly as this can have a withdrawal effect and produce temporary vitamin C deficiency symptoms.

Sources Of Vitamin C

• Citrus fruits (lemon, lime, orange, grapefruit)

• Peppers

• Strawberries

• Kiwi

• Broccoli

• Blackcurrants

• Sprouts

Should You Supplement Vitamin C?

Generally, a healthy diet will give you all the vitamin C you need. Most multi-vitamins have high amounts of vitamin C too. Still, if you do decide to supplement vitamin C, you should not take high amounts for extended periods of time, as this can cause scurvy-like withdrawal symptoms if it is not reduced slowly.

Always consult your GP or doctor before supplementing vitamin C as for some health conditions it can react with vitamin C and have adverse effects.

Recent Posts

See All