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Water-soluble vitamins: C and B complex

A comprehensive overview of the water-soluble vitamins

There are nine water-soluble vitamins in the human diet. This article examines each in detail, letting you know the best sources and how much you need.

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Water-soluble vitamins: A comprehensive overview
Last updated on September 23, 2023, and last reviewed by an expert on August 1, 2022.

Vitamins are often categorized based on their solubility.

Water-soluble vitamins: A comprehensive overview

Most of them dissolve in water and are called water-soluble vitamins. In contrast, there are only four fat-soluble vitamins, which dissolve in oil (liquid fat).

Nine water-soluble vitamins are found in the human diet:

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Unlike fat-soluble vitamins, water-soluble vitamins are generally not stored in the body. For this reason, you should try to get them regularly from your diet.

This article provides a detailed overview of the water-soluble vitamins — their functions, health benefits, dietary sources, recommended intake, and more.

Thiamine (vitamin B1)

Thiamine, also known as vitamin B1, was the first water-soluble vitamin to be described scientifically.

Types of vitamin B1

Many forms of thiamine exist, including:

Role and function of vitamin B1

Like the other B vitamins, thiamine is a coenzyme in the body. This applies to all its active forms, but thiamine pyrophosphate is the most important one.

Coenzymes are small compounds that help enzymes trigger chemical reactions that otherwise wouldn’t happen on their own.

Thiamine is involved in many essential chemical reactions. For instance, it helps convert nutrients into energy and supports sugar formation.

Dietary sources of vitamin B1

The richest dietary sources of thiamine include nuts, seeds, whole grains, liver, and pork.

In contrast, fruits, vegetables, and dairy products generally do not provide much thiamine.

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The list below shows the recommended daily allowance (RDA) for thiamine.

The RDA for infants hasn’t been established. Instead, the table shows the adequate intake. The adequate intake is like the RDA but based on weaker evidence.

Vitamin B1 deficiency

Deficiency is uncommon, but high blood sugar levels may increase thiamine elimination via urine, raising its requirements and the risk of deficiency. Thiamine levels may be reduced by 75–76% in people with type 1 and type 2 diabetes.

People with alcoholism are also at an increased risk for deficiency because of a poor diet and impaired thiamine absorption.

Serious deficiency may lead to disorders known as beriberi and Wernicke-Korsakoff syndrome.

These disorders are associated with various symptoms, including anorexia, weight loss, impaired neural function, mental problems, muscle weakness, and heart enlargement.

Vitamin B1 side effects and toxicity

Thiamine is considered safe. There are no reports of adverse effects after consuming high amounts of thiamine from food or supplements.

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This is partly because excess thiamine is quickly excreted from the body in urine.

As a result, thiamine’s tolerable upper intake level has not been established. However, this does not rule out possible symptoms of toxicity at very high intakes.

Benefits of vitamin B1 supplements

No evidence shows that thiamine supplements benefit healthy people who get adequate amounts from their diets.

But for those with high blood sugar levels or a poor thiamine status, high-dose supplements may reduce blood sugar and blood pressure.

Additionally, low thiamine intake has been associated with various other disorders, such as glaucoma, depression, and fibromyalgia. However, more research is needed before strong conclusions can be made.

Summary of vitamin B1

Thiamine, also known as vitamin B1, was the first B vitamin to be discovered.

Like the other B vitamins, thiamine acts as a coenzyme. It is essential in many metabolic processes, including converting nutrients into energy.

The richest dietary sources of thiamine include liver, pork, seeds, and whole-grain cereals. Deficiency is uncommon, but diabetes and excessive alcohol intake increase the risk. Serious deficiency may result in diseases such as beriberi and Wernicke-Korsakoff syndrome.

High-dose thiamine supplements do not seem to have adverse effects, and the tolerable upper intake level hasn’t been established. However, supplements do not appear to benefit those who get adequate amounts from their diets.

Riboflavin (vitamin B2)

Riboflavin is the only water-soluble vitamin used as a food coloring. It is named for its color — the Latin word flavus means “yellow.”

Types of vitamin B2

In addition to riboflavin, dietary substances known as flavoproteins release riboflavin during digestion.

Two of the most common flavoproteins are flavin adenine dinucleotide and flavin mononucleotide. They are found in a wide range of foods.

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Role and function of vitamin B2

Riboflavin functions as a coenzyme in various chemical reactions.

Like thiamine, it is involved in the conversion of nutrients into energy. It is also required in converting vitamin B6 to its active form and in converting tryptophan to niacin (vitamin B3).

Dietary sources of vitamin B2

Yeast extract spread is also exceptionally rich in riboflavin, containing around 18 mg in every 100 grams. Other good sources of riboflavin include eggs, leafy vegetables, broccoli, milk, legumes, mushrooms, and meat.

Additionally, riboflavin is often added to processed breakfast cereals and is used as a yellow-orange food coloring.

The list below shows the RDA or adequate intake for riboflavin. These values represent the daily intake sufficient to meet most people’s requirements.

Vitamin B2 deficiency

Riboflavin deficiency is very rare in developed countries. However, a poor diet, old age, lung diseases, and alcoholism may increase the risk.

Severe deficiency results in a condition known as ariboflavinosis, characterized by a sore throat, inflamed tongue, anemia, and skin and eye problems.

It also impairs the metabolism of vitamin B6 and the conversion of tryptophan to niacin.

Vitamin B2 side effects and toxicity

A high intake of dietary or supplemental riboflavin has no known effects on toxicity.

Absorption becomes less efficient at higher doses. Also, very small amounts are stored in body tissues, and excess riboflavin is flushed out of the body with urine.

As a result, riboflavin’s safe upper intake level has not been established.

Benefits of vitamin B2 supplements

In most cases, riboflavin supplements do not benefit people who already get enough from food.

Yet, low-dose riboflavin supplements may reduce blood pressure and lower the risk of heart disease in people genetically predisposed to them. It’s thought to decrease high homocysteine levels in those with two copies of the gene MTHFR 677TT.

Higher doses of riboflavin, such as 200 mg twice a day, may also reduce migraines.

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Summary of vitamin B2

Riboflavin, also known as vitamin B2, is a coenzyme with various essential functions. For instance, it is required for converting nutrients to energy.

Found in various foods, its richest sources include liver, meat, dairy products, eggs, leafy vegetables, almonds, and legumes.

Deficiency is virtually unknown among healthy people in Western countries, although diseases and poor lifestyle habits may increase the risk.

High-dose riboflavin supplements are not known to have any adverse effects, but they usually only benefit those deficient. However, evidence suggests they may reduce migraines or lower the risk of heart disease in genetically susceptible people.

Niacin (vitamin B3)

Niacin, also known as vitamin B3, is the only B vitamin your body can produce from another nutrient — the amino acid tryptophan.

Types of vitamin B3

Niacin is a group of related nutrients. The most common forms are:

The compound nicotinamide riboside also has vitamin B3 activity. It is found in trace amounts in whey protein and baker’s yeast.

Role and function of vitamin B3

All dietary forms of niacin are eventually converted into nicotinamide adenine dinucleotide (NAD+) or nicotinamide adenine dinucleotide phosphate (NADP+), which act as coenzymes.

Like the other B vitamins, it functions as a coenzyme in the body, playing an essential role in cellular function and acting as an antioxidant.

One of its most important roles is to drive a metabolic process known as glycolysis, the extraction of energy from glucose (sugar).

Dietary sources of vitamin B3

Yeast extract spread is exceptionally rich in niacin, providing around 128 mg every 100 grams.

Other good sources include fish, chicken, eggs, dairy products, and mushrooms. Niacin is also added to breakfast cereals and flour.

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Additionally, your body can synthesize niacin from the amino acid tryptophan. Scientists have estimated that 60 mg of tryptophan can be used to create 1 mg of niacin.

The list below shows the RDA or adequate intake for niacin. These values are the estimated amount of niacin that most people (97.5%) need to get from their diets every day.

It also shows the tolerable upper intake limit (UL), the highest daily intake considered safe for most people.

Infants (0–6 months)

Infants (7–12 months)

Children (1–3 years)

Children (4–8 years)

Children (9–13 years)

Women (14+ years)

Men (14+ years)

Pregnancy

Lactation

Vitamin B3 deficiency

Niacin deficiency, known as pellagra, is uncommon in developed countries.

The main symptoms of pellagra include inflamed skin, mouth sores, diarrhea, insomnia, and dementia. Like all deficiency diseases, it is fatal without treatment.

Fortunately, you can easily get all the niacin you need from a varied diet.

Deficiency is much more common in developing countries where people commonly follow diets that lack diversity.

Cereal grains are especially low in available niacin since most of it is bound to fiber in the form of niacytin.

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However, your body can synthesize it from the amino acid tryptophan. As a result, severe niacin deficiency can often be avoided on a high-protein diet.

Vitamin B3 side effects and toxicity

Naturally occurring niacin from food does not appear to have any adverse effects.

However, high supplemental doses of niacin may cause niacin flush, nausea, vomiting, stomach irritation, and liver damage.

Niacin flush is a side effect of immediate-release nicotinic acid supplements. It is characterized by a flush in the face, neck, arms, and chest.

Liver damage is associated with the long-term use of very high doses (3–9 grams per day) of sustained-release or slow-release nicotinic acid.

Additionally, taking niacin supplements for a long time may increase insulin resistance and raise blood sugar levels.

Nicotinic acid may also increase the circulating levels of uric acid, worsening symptoms in people predisposed to gout.

Benefits of vitamin B3 supplements

Nicotinic acid supplements at doses ranging from 1,300–2,000 mg per day are commonly used to normalize blood lipid levels.

They bring down high levels of “bad” low-density-lipoprotein (LDL) cholesterol while raising levels of “good” high-density lipoprotein (HDL) cholesterol when they are low. Triglyceride levels may also drop in those taking supplements.

Some studies also suggest nicotinic acid reduces heart disease risk, but its benefits are controversial, and study results have been inconsistent.

Preliminary evidence also indicates that niacin supplements may improve cognition, but further studies are needed before strong claims can be made.

Summary of vitamin B3

Niacin, also known as vitamin B3, is a group of two related compounds — niacinamide and nicotinic acid. They serve many vital functions in the body.

Niacin is found in many different foods, such as liver, fish, poultry, eggs, dairy products, sunflower seeds, and peanuts, to name a few. Additionally, it is commonly added to processed food like flour and breakfast cereals.

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Deficiency is rare in Western nations. People who eat low-protein diets that lack diversity is at an increased risk.

High-dose nicotinic acid supplements are commonly used to normalize blood lipid levels, although some scientists doubt the vitamin’s benefits for heart health.

But supplements may also have negative side effects, such as liver damage, reduced insulin sensitivity, and niacin flush.

Pantothenic acid (vitamin B5)

Pantothenic acid is found in virtually all food. Appropriately, its name is derived from the Greek word pantothen, which means “from every side.”

Types of vitamin B5

Multiple forms of pantothenic acid or compounds release the active form of the vitamin when digested. In addition to free pantothenic acid, these include:

Role and function of vitamin B5

Pantothenic acid plays a key role in a wide range of metabolic functions.

It is required to form coenzyme A, which is necessary for synthesizing fatty acids, amino acids, steroid hormones, neurotransmitters, and other important compounds.

Dietary sources of vitamin B5

Pantothenic acid is found in virtually all food.

Other rich sources include spreading yeast, shiitake mushrooms, caviar, kidneys, chicken, beef, and egg yolks.

Several plant foods are also good sources. In addition to those mentioned above, these include root vegetables, whole grains, tomatoes, and broccoli.

Like many other B vitamins, pantothenic acid is often added to breakfast cereals.

The list below shows most people’s adequate intake (AI) of pantothenic acid. The RDA has not been established.

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Vitamin B5 deficiency

Pantothenic acid deficiency is rare in industrialized countries. This vitamin is so widespread in foods that deficiency is virtually unheard of, except in severe malnutrition.

However, its requirements may be higher in people with diabetes and those who regularly consume excessive alcohol.

Studies in animals show that pantothenic acid deficiency harms most organ systems. It is associated with numerous symptoms, including numbness, irritability, sleep disturbances, restlessness, and digestive problems.

Vitamin B5 side effects and toxicity

Pantothenic acid does not appear to have any adverse effects at high doses. The tolerable upper limit has not been established.

However, large doses like 10 grams per day may cause digestive discomfort and diarrhea.

In mice, the lethal dose was estimated to be around 4.5 grams for each pound of body weight (10 grams per kg), equivalent to 318 grams for a 154-pound (70-kg) human.

Benefits of vitamin B5 supplements

Studies have not provided any good evidence of benefits from pantothenic acid supplements in people who get adequate amounts from their diets.

While people take supplements to treat various disorders, including arthritis, dry eyes, and skin irritation, there is no strong evidence for their effectiveness in treating any of these disorders.

Summary of vitamin B5

Pantothenic acid, also known as vitamin B5, plays various important roles in metabolism.

Almost all food contains this vitamin. The best sources include liver, sunflower seeds, mushrooms, root vegetables, and whole grains.

Since pantothenic acid is widespread in foods, deficiency is virtually unknown and is usually only associated with severe malnutrition.

Supplements are safe and do not have any adverse effects. However, very high doses may cause diarrhea and other digestive issues.

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Although some people regularly take pantothenic acid supplements, there is currently no strong evidence for their effectiveness in treating diseases in those who get adequate amounts from food.

Vitamin B6

Vitamin B6 is a group of nutrients required for synthesizing pyridoxal phosphate, a coenzyme involved in more than 100 different metabolic processes.

Types of vitamin B6

Like the other B vitamins, vitamin B6 is a family of related compounds, such as:

In the liver, all dietary forms of vitamin B6 are converted into pyridoxal 5-phosphate, the active form of the vitamin.

Role and function of vitamin B6

Like other B vitamins, vitamin B6 acts as a coenzyme in numerous chemical reactions.

It is involved in red blood cell formation, energy, and amino acid metabolism. It is also required to release glucose (sugar) from glycogen, the molecule the body uses to store carbs.

Vitamin B6 also supports the formation of white blood cells and helps the body synthesize several neurotransmitters.

Dietary sources of vitamin B6

Other good sources include tuna, pork, turkey, bananas, chickpeas, and potatoes. Vitamin B6 is also added to breakfast cereals and soy-based meat substitutes.

The availability of this vitamin is generally higher in animal-sourced foods than plant foods.

The list below shows the RDA for vitamin B6. The RDA is the daily intake estimated to be sufficient for most people.

The RDA hasn’t been established for infants, so adequate intake (AI) is presented instead.

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Infants (0–6 months)

Infants (7–12 months)

Children (1–3 years)

Children (4–8 years)

Children (9–13 years)

Women (14–18 years)

Women (19–50 years)

Women (51+ years)

Men (14–18 years)

Men (19–50 years)

Men (51+ years)

Pregnancy

Lactation

Vitamin B6 deficiency

Vitamin B6 deficiency is rare. People with alcoholism are at the greatest risk.

The main symptoms include anemia, skin rashes, convulsions, confusion, and depression.

Deficiency has also been associated with an increased risk of cancer.

Vitamin B6 side effects and toxicity

Naturally occurring vitamin B6 from food does not seem to have any adverse effects.

In contrast, very large supplemental doses of pyridoxine — 2,000 mg daily or more — are linked to sensory nerve damage and skin lesions.

A high intake of pyridoxine supplements may also suppress milk production in breastfeeding women.

Benefits of vitamin B6 supplements

Large doses of pyridoxine have been used to treat carpal tunnel and premenstrual syndrome.

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However, its benefits are controversial. No strong evidence proves that pyridoxine supplements effectively treat these conditions.

Because of the adverse health effects of high-dose pyridoxine supplements should only be taken under medical supervision.

Summary of vitamin B6

Vitamin B6 is a group of nutrients required for forming pyridoxal phosphate, a coenzyme that plays a vital role in numerous metabolic pathways.

The richest dietary sources are liver, salmon, sunflower seeds, and pistachio nuts, to name a few.

Deficiency is rare, although regularly drinking high amounts of alcohol may raise the risk.

High supplemental doses may cause nerve damage and skin lesions, but getting vitamin B6 from food doesn’t appear to have any negative effects.

While adequate vitamin B6 intake is healthy, no good evidence demonstrates that vitamin B6 supplements are useful in treating diseases.

Biotin (vitamin B7)

People often take biotin supplements to nourish their hair, nails, and skin, although strong evidence for these benefits is lacking. It was historically called vitamin H after the German word “haut”, meaning “skin”.

Types of vitamin B7

Biotin is either found in its free form or bound to proteins.

When proteins that contain biotin are digested, they release a compound called biocytin. The digestive enzyme biotinidase breaks biocytin into free biotin and lysine, an amino acid.

Role and function of vitamin B7

Same as all B vitamins, biotin functions as a coenzyme. Five carboxylases are required to function, enzymes involved in several fundamental metabolic processes.

For instance, biotin is essential in fatty acid synthesis, glucose formation, and amino acid metabolism.

Dietary sources of vitamin B7

Compared to the other B vitamins, biotin doesn’t have as much research behind its content in food.

Animal-sourced biotin-rich foods include organ meats, fish, meat, egg yolk, and dairy products. Good plant sources include legumes, leafy greens, cauliflower, mushrooms, and nuts.

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Your gut microbiota also produces small amounts of biotin.

The list below shows the adequate intake (AI) for biotin. The AI is similar to the RDA but is based on weaker research.

Vitamin B7 deficiency

Biotin deficiency is relatively uncommon.

The risk is greatest among infants fed formula low in biotin, people taking antiepileptic medications, infants with Leiner’s disease, or people genetically predisposed to deficiency.

Untreated biotin deficiency can cause neurological symptoms, such as seizures, intellectual disability, and loss of muscle coordination.

Deficiency has also been reported in animals fed high amounts of raw egg whites. Egg whites contain a protein called avidin, which prevents the absorption of biotin.

Vitamin B7 side effects and toxicity

Biotin does not have any known adverse effects at high doses and the tolerable upper limit has not been established.

Benefits of vitamin B7 supplements

Limited evidence suggests that biotin supplements may improve health in those who otherwise get adequate amounts from their diets.

For instance, studies suggest biotin may improve symptoms in people with multiple sclerosis (MS).

Observational studies also indicate that biotin supplements may improve brittle nails in women. However, higher quality studies are needed before any claims can be made.

Summary of vitamin B7

Biotin, also known as vitamin B7, is a coenzyme required for many key metabolic processes.

It is found in a wide range of foods. Good sources include organ meats, egg yolk, meat, legumes, cauliflower, mushrooms, and nuts.

Deficiency is uncommon and adverse effects are unknown, even at high supplemental doses. Further studies need to establish the tolerable upper intake level.

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Limited evidence supports the use of biotin supplements among people who already get adequate amounts from their diets. However, a few studies suggest they may improve the symptoms of MS and strengthen brittle nails.

Vitamin B9

Vitamin B9 was first discovered in yeast but later isolated from spinach leaves. For this reason, it was given the name folic acid or folate, words derived from the Latin word folium, meaning “leaf.”

Types of vitamin B9

Vitamin B9 comes in several different forms, including:

Role and function of vitamin B9

Vitamin B9 is a coenzyme essential for cell growth, DNA formation, and amino acid metabolism.

It is crucial during rapid cell division and growth, such as infancy and pregnancy.

Additionally, it is required to form red and white blood cells, so deficiency may lead to anemia.

Dietary sources of vitamin B9

Other good sources include leafy greens, legumes, sunflower seeds, and asparagus. Yeast extract spread is exceptionally rich in vitamin B9, providing around 3,786 mcg per 100 grams.

Folic acid is also frequently added to processed food products.

The table below shows the recommended daily allowance (RDA) for vitamin B9. It also presents the daily tolerable upper limit (UL), the amount considered safe for most people.

The RDA for infants hasn’t been established. Instead, the table shows the adequate intake values.

Infants (0–6 months)

Infants (7–12 months)

Children (1–3 years)

Children (4–8 years)

Children (9–13 years)

Adolescents (14–18 years)

Adults (19+ years)

Pregnancy

Lactation

Vitamin B9 deficiency

Vitamin B9 deficiency rarely occurs on its own. It is usually associated with other nutrient deficiencies and a poor diet.

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Anemia is one of the classic symptoms of vitamin B9 deficiency. It is indistinguishable from the anemia associated with vitamin B12 deficiency.

Lack of vitamin B9 may also lead to brain or neural chord birth defects, collectively known as neural tube defects.

Vitamin B9 side effects and toxicity

No serious adverse effects of high vitamin B9 intake have been reported.

Yet, studies show that high-dose supplements may mask vitamin B12 deficiency. Some even suggest that they may worsen the neurological damage associated with vitamin B12 deficiency.

Additionally, some scientists are concerned that a high intake of folic acid — a synthetic form of vitamin B9 — may cause health problems.

Benefits of vitamin B9 supplements

There is not much evidence that folic acid supplements benefit healthy people following a balanced diet.

A few studies suggest that supplements may reduce the risk of heart disease, improve blood sugar control and slightly reduce the symptoms of depression.

However, the benefits of taking vitamin B9 supplements may only be seen in those low in the vitamin, to begin with.

Summary of vitamin B9

Like all other B vitamins, vitamin B9 acts as a coenzyme. It is essential for cell growth and various key metabolic functions.

It is found in both plants and animals. Rich sources include liver, legumes, and leafy greens.

Deficiency in vitamin B9 is uncommon. The main symptom is anemia, but in pregnant women, low levels also raise the risk of birth defects. High intake doesn’t have any serious adverse effects.

The benefits of supplements are unclear for those who get enough vitamin B9 from their diet. But studies suggest they may reduce the risk of heart disease and lower blood sugar levels.

Vitamin B12 (cobalamin)

Vitamin B12 is the only vitamin that contains a metallic element, namely cobalt. For this reason, it is often referred to as cobalamin.

Types of vitamin B12

There are four main types of vitamin B12 — cyanocobalamin, hydroxocobalamin, adenosylcobalamin, and methylcobalamin.

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They can be found in supplements, although cyanocobalamin is the most common. It is considered ideal for supplements due to its stability but is only found in trace amounts in food.

Hydroxocobalamin is the most common naturally occurring form of vitamin B12 and is widely found in animal-sourced foods.

The other natural forms methylcobalamin and adenosylcobalamin have become popular as supplements in recent years.

Role and function of vitamin B12

Like all other B vitamins, vitamin B12 acts as a coenzyme.

Adequate intake helps maintain brain function and development, neurological function, and the production of red blood cells.

It is also required for converting protein and fat into energy and is essential for cell division and DNA synthesis.

Dietary sources of vitamin B12

Animal-sourced foods are virtually the only dietary source of vitamin B12. These include meat, dairy products, seafood, and eggs.

Other rich sources include other types of liver, heart, octopus, oysters, herring, and tuna.

However, tempeh and a few algae, such as nori seaweed, may also contain small amounts of vitamin B12. Whether these foods can provide sufficient amounts is a matter of debate.

Other algae, like spirulina, contain pseudovitamin B12, a group of compounds similar to vitamin B12 but unusable by the body.

The table below shows the RDA for vitamin B12. As usual, the RDA hasn’t been established for infants, so adequate intake (AI) is presented instead.

Vitamin B12 deficiency

Vitamin B12 is stored in the liver, so it may take a long time for deficiency symptoms to develop even if you aren’t getting enough of it.

Those at the greatest risk of deficiency are those who never or rarely eat animal-sourced foods. This includes vegetarians and vegans.

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Deficiency may also develop in older people. Many require regular vitamin B12 injections.

Vitamin B12 absorption depends on a protein produced by the stomach called intrinsic factor. As people age, the formation of intrinsic factors may reduce or stop altogether.

Other risk groups include those who have had weight loss surgery or suffer from Crohn’s disease or celiac disease.

Deficiency may cause various health problems, such as anemia, appetite loss, sore tongue, neurological problems, and dementia.

Vitamin B12 side effects and toxicity

Only a small proportion of vitamin B12 can be absorbed from the digestive tract. The amount absorbed depends on the production of intrinsic factors in the stomach.

As a result, no adverse effects have been linked with high intake of vitamin B12 in healthy people. The tolerable upper intake level has not been established.

Benefits of Vitamin B12 supplements

While vitamin B12 supplements benefit people at risk of deficiency, less is known about their effects among those who get adequate amounts from their diets.

One small study suggests that taking 1,000 mcg per day may improve verbal learning in people recovering from strokes, but more research is needed.

Additionally, hydroxocobalamin injections treat cyanide poisoning, usually in combination with sodium thiosulfate.

Summary of vitamin B12

Vitamin B12 functions as a coenzyme and plays a vital role in many metabolic pathways. It also helps maintain neurological function and the formation of red blood cells.

It is found in virtually all animal-sourced foods but is absent from plant foods.

As a result, vegans are at risk of deficiency or poor vitamin B12 status. Older people are also at risk because of impaired absorption. Anemia and impaired neurological function are classic deficiency symptoms.

High supplemental intake doesn’t have any known adverse effects. No strong evidence shows that they have benefits either, at least not in those who get adequate amounts from their diets.

Vitamin C

Vitamin C is the only water-soluble vitamin that doesn’t belong to the vitamin B category. It is one of the body’s main antioxidants and is required for collagen synthesis.

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Types of vitamin C

Vitamin C comes in two forms, the most commonly known as ascorbic acid.

An oxidized form of ascorbic acid called dehydroascorbic acid also has vitamin C activity.

Role and function of vitamin C

Vitamin C supports many essential body functions, including:

Unlike the B vitamins, vitamin C doesn’t act as a coenzyme, although it is a cofactor for prolyl hydroxylase, an enzyme that serves an essential role in the formation of collagen.

Dietary sources of vitamin C

The main dietary sources of vitamin C are fruits and vegetables.

Cooked animal-sourced foods contain virtually no vitamin C, but low amounts can be found in raw liver, eggs, fish roe, meat, and fish.

Cooking or drying foods significantly reduces their vitamin C content.

The recommended daily allowance (RDA) of vitamin C is the estimated amount of the vitamin most people need every day.

The table below also shows the tolerable upper limit (UL), the highest intake level thought to be completely safe for most people.

No RDA has been established for infants. Instead, scientists have estimated their adequate intake, similar to the RDA, but based on weaker evidence.

Infants (0–6 months)

Infants (7–12 months)

Children (1–3 years)

Children (4–8 years)

Children (9–13 years)

Women (14–18 years)

Women (19+ years)

Men (14–18 years)

Men (19+ years)

Pregnancy

Lactation

Vitamin C deficiency

Deficiency is rare in Western countries but may develop in people who follow restrictive diets or eat almost no fruits or vegetables. People with drug addiction or alcoholism are also at greater risk.

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It leads to a disease known as scurvy, characterized by the breakdown of connective tissue.

The first symptoms of deficiency include fatigue and weakness. As scurvy becomes worse, people may experience spotted skin and inflamed gums.

Advanced scurvy may cause loss of teeth, bleeding gums, skin, joint problems, dry eyes, swelling, and impaired wound healing. Like all vitamin deficiencies, scurvy is fatal without treatment.

Vitamin C side effects and toxicity

Most people tolerate high doses of vitamin C without any side effects.

However, high doses exceeding 3 grams daily cause diarrhea, nausea, and abdominal cramps. This is because only a limited amount of vitamin C can be absorbed from a single dose.

High-dose supplements over 1,000 mg per day may also increase predisposed people’s risk of kidney stones.

Benefits of vitamin C supplements

There is mixed evidence that vitamin C supplements benefit people who get adequate amounts from the diet.

However, vitamin C can improve iron absorption from a meal, helping those who are low in iron.

Additionally, one analysis of 29 studies concluded that supplements that provide at least 200 mg of vitamin C per day might help you recover from the common cold.

While vitamin C supplements may also help lower blood pressure, there is no evidence that they reduce the risk of heart disease.

Studies also suggest vitamin C may reduce the risk of cognitive decline, improve blood vessel function and reduce blood sugar levels, but high-quality studies are needed before definite conclusions can be reached.

Summary of vitamin C

Vitamin C is a powerful antioxidant that’s vital for the maintenance of connective tissue.

The main dietary sources are fruits and vegetables, but low amounts can be acquired from raw animal-sourced foods. Deficiency, known as scurvy, is rare in developed countries.

Most people tolerate high-dose supplements without any adverse effects. However, studies on the benefits of vitamin C supplements have had mixed results, suggesting supplements may not be that useful for those who already get sufficient amounts from their diets.

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Summary

Most vitamins are water-soluble. These include the eight B vitamins as well as vitamin C.

Their roles in the body range widely, but most function as coenzymes in numerous metabolic pathways.

All the water-soluble vitamins are easy to get from a balanced diet. However, vitamin B12 is only found in substantial amounts in animal-sourced foods. As a result, vegans are at a high risk of deficiency and may need to take supplements or get regular injections.

Remember that your body generally doesn’t store water-soluble vitamins, except for vitamin B12. Optimally, you should get them from your diet every day.

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