Vitamin B: The definitive guide

 yoghurt and cereal, vitamin b

 Author Miriam Ferrer, PhDLast updated 13th July 2020

Ingredients & Nutrition

Vitamin B: The definitive guide

The B-vitamins play a vital role in cell metabolism. This group of water-soluble vitamins includes eight different compounds, generally known as vitamin B complex. These are Thiamin (B1), Riboflavin (B2), Niacin (B3), Pantothenic Acid (B5), Pyridoxine (B6), Biotin (B7), Folate (B9) and cobalamin (B12).

The list is long, but each one is unique in its effects on our bodies, as well as which foods are the best ones to consume for each vitamin. Outlined below is information about each vitamin B compound and the symptoms experienced if you are deficient in any one of them.

  • What is Vitamin B1 or Thiamin
  • What is Vitamin B2 or Riboflavin
  • What is Vitamin B3 or Niacin
  • What makes Niacin different from the other B vitamins
  • What is Vitamin B5 or Pantothenic Acid
  • What is Vitamin B6 or Pyridoxine
  • What is Vitamin B7 or Biotin
  • What is Vitamin B9 or Folate
  • What is Vitamin B12 or Cobalamin
  • Summary
  • References

What is Vitamin B1 or Thiamin

Vitamin B1, also known as thiamin, according to Harvard Health, plays a vital role in the growth and function of various cells. It can keep the nervous system strong and healthy, as well as allowing energy to be broken down and released from the food we consume. The current guidelines recommend a daily intake of 0.1 mg (milligrams) thiamin/MJ (miliJoules), or 0.4mg/1,000 kcal daily for all adults. This nomenclature has been established because the thiamin requirement is related to energy requirement1.

Side of effects of B1 or thiamin deficiency

When it comes to the deficiency of thiamin, it is more of a rarity to become heavily deficient to the point of sickness. However, a severe lack of B1 can cause several cognitive problems in the brain and heart.

A minor deficiency will see you looking at weight loss, confusion or memory loss, muscle weakness, peripheral neuropathy and lowered immunity. Therefore, a diet rich in meats, fish and whole grains will naturally give you the necessary intake you need. You can also look for fortified cereals, green peas, sunflower seeds and yoghurt.

Heavy consumption of coffee, chocolate and tea, foods that are rich in tannins and caffeine and theobromine, can affect thiamin absorption2.

What is Vitamin B2 or Riboflavin

Vitamin B2, also known as riboflavin, is an important B vitamin that is vital for growth and red blood cell production. Riboflavin is a central component of the cofactors FAD (flavin adenosine dinucleotide) and FMN (flavin mononucleotide), which are involved in many metabolic reactions. For example, glutathione reductase, an important antioxidant enzyme, depends on FAD. Antioxidants are known to fight free radicals which damage cells and DNA.

Side effects of Riboflavin or B2 deficiency

A healthy diet of whole-grain products, vegetables and some meat will see to your riboflavin needs. Clinical riboflavin deficiency is rare; however, Penn State Hershey Medical Center suggests that symptoms include “fatigue, slowed growth, digestive problems, cracks and sores around the mouth, swollen magenta-coloured tongue, eye fatigue, swelling and sore throat and sensitivity to light.” Riboflavin is also very important for vitamin B6 and folate (B9) metabolism, as it changes them into forms that the body can use. The recommended amount for adults is 1.6mg/day3.

Your best sources will come from almonds, organ meats, whole grains, mushrooms, soybeans, milk, yoghurt, eggs, broccoli, brussels and spinach. However, riboflavin is known to be destroyed by light, therefore vitamin B2 rich foods should be stored in a dark cool room.

If you are consuming these foods as a part of a healthy diet, it provides protection against cataracts and the reduction of migraines.

What is Vitamin B3 or Niacin

bowl of spinach

Vitamin B3, niacin, is able to lower or suppress inflammation, improve circulation and interestingly, aid in the bodies ability to make “sex and stress-related hormones in the adrenal glands” according to Penn State Hershey Medical Center.

Niacin is mainly found in two forms in the body, nicotinic acid and nicotinamide, which are used by the body to make the cofactors NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate). NAD is essential for energy metabolism, while NAPD is needed for hormone production.

Side effects of Niacin or B3 deficiency

With adequate levels of vitamin B3, you could improve the symptoms of arthritis, lower the risk of Alzheimer disease and having cataracts and it can help skin conditions.

Further studies are being undertaken on ADHD, migraines, dizziness, depression, motion sickness and alcohol dependence. Deficiency is rare, and it’s commonly associated with alcoholism; symptoms can include indigestion, fatigue, canker sores, vomiting, poor circulation and depression.

You can find B3 in food sources such as beetroots, beef liver, beef kidney, seafood, sunflower seeds and peanuts. In the UK, as many other countries, commercial flour is fortified with niacin, making deficiency rare.

What makes Niacin different from the other B vitamins

Niacin is different from other B vitamins in that it can be produced by the body if there is enough supply of the amino acid tryptophan. For this reason, dietary requirements tend to be expressed as niacin equivalents (NEs). 1 NE equals 1 mg niacin, or 60mg of tryptophan, which can be converted into niacin. The current guidelines recommend a daily intake of 1.6mg NE/MJ (miliJoules) daily for adults4.

If you are looking at vitamin B3 supplements, make sure you read the label as it can come in different forms, which will have different bioavailability and effect.

Excessive intake from nicotinic acid can produce skin flushing, and therefore it is not recommended to take supplements containing high levels of nicotinic acid for a long period of time.

What is Vitamin B5 or Pantothenic Acid

Vitamin B5, commonly known as pantothenic acid, plays a central role in intermediary metabolismas part of the coenzyme A (CoA) molecule. It is needed for energy, to produce red blood cells and just like B3, can produce “sex and stress-related hormones”, as stated by Penn State Hershey Medical Center. Pantothenic acid is needed for the synthesis of acetylcholine, a neurotransmitter involved in cognition and memory. It is also beneficial as it aids in the body's absorption of other vitamins, specifically riboflavin, and can maintain a healthy digestive tract.

Found in an extensive number of fresh foods, like whole unprocessed grains, vegetables, meats and seafood, it is known as the vitamin that is everywhere. Adults aged nineteen and older should try to get 5mg daily5.

Side effects of Pantothenic or B5 deficiency

Deficiency of vitamin B5, though rare, can lead to symptoms including: “fatigue, insomnia, depression, irritability, vomiting, stomach pains, burning feet and upper respiratory infections” Adequate levels have been seen to reduce cholesterol, aid in skincare and wound healing and may improve symptoms of rheumatoid arthritis.

What is Vitamin B6 or Pyridoxine

vitamin b6 food with chickpeas

Vitamin B6, known as pyridoxine, is found in several forms, all of them interchangeable. Pyridoxal 5’- phosphate (PLP or P5P), regarded as the biologically active form of B6, can, according to Harvard Health, “assist more than 100 enzymes to perform various functions, including the breakdown of proteins, carbohydrates, and fats; maintaining normal levels of homocysteine (since high levels can cause heart problems); and support immune function and brain health.”

When our B6 levels are at an adequate level, we could be looking at lower risks of cancer, decreasing our risk of cardiovascular diseases and gaining better cognitive functions. It is also able to decrease levels of homocysteine in the body, an amino acid that in high levels has been associated with heart disease.

Side effects of Pryidoxine or B6 deficiency

When we are deficient in B6, it typically means we are lacking vitamin B12 and folate in the body too. You may not be looking at any symptoms with a small deficiency, yet higher deficiencies can be linked to microcytic anaemia, skin conditions, depression, confusion and lowered immunity.

Some medical conditions are also able to lead to vitamin B6 deficiency due to absorption issues. This could come from conditions such as kidney disease, autoimmune intestinal disorders, autoimmune inflammatory or alcoholism.

To make sure you have an adequate intake of vitamin B6, try to consume foods such as; beef liver, tuna, salmon, fortified cereals, chickpeas, poultry, dark leafy greens, bananas and oranges.

The recommended amount is very dependent on your age group. Men between the ages of fourteen to fifty need 1.3mg a day whilst fifty-one year olds and older need 1.7mg. Women between the ages of nineteen to fifty need 1.3mg and fifty one year olds and older need 1.5mg daily6.

Having too little vitamin B6 is problematic, but so is having too much. High intakes of vitamin B6 have been associated with sensory neuropathy which means the body’s sensory nerves become damaged. Therefore, it is not recommended to take supplements with high doses of pyridoxine (over 10mg) for long periods of time7.

What is Vitamin B7 or Biotin

chopping salmon

Vitamin B7, commonly known as biotin, is often a vitamin found in beauty products that promote healthy hair, skin and nails. Although these parts will suffer if we are deficient in this specific vitamin, it doesn’t necessarily mean that taking more will lead to healthier versions.

Nevertheless, Harvard Health states that adequate levels of biotin “help to regulate signals sent by cells and the activity of genes” as well as “assisting enzymes to break down fats, carbohydrates and proteins in food.” Biotin is an important component of enzymes that are involved in the metabolism of amino acids and fatty acids. It is also involved in DNA division.

Biotin is found in food sources like beef liver, cooked eggs, avocados, salmon, pork, sweet potato, nuts and seeds. As for eggs, if you are someone who enjoys the consumption of raw eggs, you may want to rethink your decision. Avidin, a protein present in egg whites, tends to bind to biotin therefore preventing its absorption.

Side effects of Biotin or vitamin B7 deficiency

Despite a deficiency being rare, as outlined earlier, you could experience thinning hair, brittle nails, or eye, nose and mouth skin rashes if you don't have adequate levels of biotin. Other factors can also lead to the malabsorption of biotin, such as alcoholism. Both men and women, nineteen years and older, should be looking at an adequate intake of around 30 µg (micrograms) daily8.

What is Vitamin B9 or Folate

Folate is the natural form of vitamin B9. Folate works as a coenzyme in the metabolism of nucleic and amino acids. Harvard Health states that, as well as aid in the form of DNA and RNA, folate is needed to “produce healthy red blood cells and is critical during periods of rapid growth, such as during pregnancy and fetal development”. Folate metabolism is interlinked with vitamin B12’s, and as some of the other B vitamins discussed above, is involved in the process of breaking down homocysteine, an amino acid associated with cardiovascular problems.

Good food sources of folate include dark leafy greens (like spinach), legumes and whole grains, fruit and seafood or liver. However, folate from food is not well absorbed, and folate deficiency has been more common than most other B vitamin deficiencies.

Signs of folate deficiency

A major sign of folate deficiency is megaloblastic anaemia,leading to fatigue, irritability and headache. Megaloblastic anaemia can also be caused by vitamin B12 deficiency. On the same note, folate and vitamin B12 play an important role in heart disease, due once again, to the control of homocysteine.

We can also see folate play a role in suppressing some early forms of cancer and lowering the risk of dementia and cognitive dysfunction.

A critical step in the folate cycle is mediated by an enzyme called MTHFR (methylenetetrahydrofolate reductase), which transforms folate into the main physiological form, 5-methyltetrahydrofate (5-MTHF). It is estimated that between 10- 25% of the population (depending on the ethnicity) have a genetic variant of this enzyme that makes it less active, putting them at risk of folate deficiency9.

Probably most of us are familiar with the central role of folate in pregnancy and fetus development, and the well-studied association between low folate intake in early pregnancy and incidence of spina bifida and other neural tube defects.

Because of that, many foods such as bread and cereals are commonly fortified with folic acid, a synthetic form of folate which has better absorption than folate from foods. In the US, manufacturers of common foods such as cereals, pasta and bread are required by law to enrich their foods with folic acid.

Recommendations for folate intake are listed as micrograms (µg) of dietary folate equivalents (DFE). This is a relatively new definition that is used because many of our foods now contain a mixture of natural folates and folic acid. Both men and women, nineteen and older, should be looking at 400µg DFE. However, those who drink alcohol regularly should look at getting 600µg DFE as alcohol consumption will slow down absorption10.

Folic Acid

Folic acid, the synthetic form of folate, is the most common form found in fortified foods and food supplements, as it is highly stable and has very good bioavailability.

Folic acid needs to be converted to folate before it can be used by the body. This can be a problem for people that have MTHFR variants, as outlined earlier, as it could lead to an excess of unmetabolised folic acid in the blood. An excess of unmetabolised folic acid has been linked to potential neurocognitive development in offspring11.

Folic acid can mask vitamin B12 deficiency, which if undetected, can cause serious health issues . For that reason, a tolerable upper limit dosage of 1mg/day has been established for folic acid intake.

Many food supplements now offer folate as 5-methyltetrahydrofolate (5-MTHF). 5-MTHF is the predominant form of folate form in food, and as such, it is readily available for the body as it doesn’t have to be converted.

In contrast to folic acid, 5-MTHF has no tolerable upper limit level and does not mask vitamin B12 deficiency. Because it doesn’t have to be converted, individuals that carry MTHFR polymorphisms should look for 5-MTHF supplements as a preferred folate form.

What is Vitamin B12 or Cobalamin

nuts and cereals

The rise in recent years of meat-exclusion diets like vegetarian and veganism has brought vitamin B12 into the spotlight.

Vitamin B12 is almost exclusively found in animal products, like seafood, liver, red meat, eggs, poultry and dairy products. People that do not eat animal products, as is the case with a vegan diet, are at risk of being deficient in this essential vitamin. When it comes to vegan options, you are looking at fortified foods such as fortified nutritional yeast, fortified cereals or enriched plant milk.

Vitamin B12 exists in several forms, which contain the mineral cobalt and are collectively known as “cobalamins”. Methylcobalamin and 5-deoxyadenosylcobalamin are the active forms in the body.

Vitamin B12 is needed for cell growth and division, as well as for the function and development of brain and nerve cells. It is essential to make haemoglobin in the red blood cells, and likely folate, is it involved in homocysteine regulation.

Side effects of Cobalamin or Vitamin B12 deficiency

Severe vitamin B12 deficiency, similarly as with folate deficiency, can lead to megaloblastic anaemia. If untreated, severe vitamin B12 deficiency could lead to irreversible neurological damage.and that’s why it is crucial to get the recommended daily amount. This is 2.5 µg daily for men and women 14 years and older12.

In food, vitamin B12 is bound to protein, and needs to be released in order to be absorbed. It is estimated that we only absorb between 30-50% of the vitamin B12 we consume from food. Most dietary supplements will give you much higher amounts than the recommended daily amount. This is because, although supplement B12 forms are easier to absorb than from food, the amount our bodies will actually take in, is generally lower than the amount in the supplement.

The most common forms of vitamin B12 found in supplements are cyanocobalamin and methylcobalamin. No significant differences have been found in the absorption rate of the different forms of cobalamin. Nevertheless, it seems that methylcobalamin might have higher tissue retention than cyanocobalamin13.

Oral supplementation is a good way to top up your vitamin B12 levels if you have restricted the intake of animal products. However, if you believe you suffer from a severe B12 deficiency you should consult your doctor.

Vitamin B deficiency can cause several forms of anaemia, nerve damage, fatigue, dementia, depression and seizures. Doctors can prescribe muscle injections or intravenous supplementation of B12 for those suffering severe deficiency.


When it comes to B vitamins, they are truly a complex set of vitamins. Understanding the differences, similarities, deficiency symptoms, the recommended daily amounts and where you can find the vitamin is difficult for most people.

If it’s too much to take in, use this guide to help you understand about the different B vitamins and how to ensure that you are consuming the correct amount of this essential vitamin.


  1. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for thiamin. EFSA Journal. 2016; 14(12):4653.
  2. Dhir S, Tarasenko M, Napoli E, Giulivi C. Neurological, psychiatric, and biochemical aspects of thiamine deficiency in children and adults. Front Psychiatry. 2019;10:207
  3. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for riboflavin. EFSA Journal. 2017; 15(8):4919.
  4. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for niacin. EFSA Journal. 2014; 12(7):3759
  5. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for pantothenic acid. EFSA Journal. 2014; 12(2):3581.
  6. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for vitamin B6. EFSA Journal. 2016; 14(5):4485.
  7. EFSA Scientific Committee on Food, Scientific Panel on Dietetic Products, Nutrition and Allergies. Tolerable upper intake levels for vitamins and minerals. EFSA. 2006.
  8. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for biotin. EFSA Journal. 2014; 12(2):3580.
  9. Obeid R, Holzgreve W, Pietrzik K. Is 5-methyltetrahydrofolate an alternative to folic acid for the prevention of neural tube defects?J Perinat Med. 2013; 41(5):469-483.
  10. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for folate. EFSA Journal. 2014; 12(11):3893.
  11. Murray LK, Smith MJ, Jadavji NM. Maternal oversupplementation with folic acid and its impact on neurodevelopment of offspring. Nutr Rev. 2018; 76(9):708-721.
  12. EFSA NDA Panel (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific opinion on dietary reference values for cobalamin (vitamin B12). EFSA Journal. 2015; 13(7):4150
  13. Paul C & Brady DM. Comparative bioavailability and utilization of particular forms of B12 supplements with potential to mitigate B12-related genetic polymorphisms. Integr Med (Encinitas). 2017; 16(1):42-49.