Vitamin B6

What is vitamin B6 ?

Vitamin B6 is a water-soluble vitamin. It is one of the vitamin B-complex group of vitamins.

There are several forms of vitamin B6. This can cause confusion because some sources (e.g. textbooks and websites) describe only one form of the vitamin, e.g. pyridoxine, presenting that as the only form of and, by implication, just another name for vitamin B6.

Elsewhere, vitamin B6 is said to exist in three forms, e.g.

  1. pyridoxine
  2. pyridoxal
  3. pyridoxamine

Still other sources list up to seven forms of vitamin B6, including:

  1. pyridoxine (PN)
  2. pyridoxine 5'-phosphate (PNP)
  3. pyridoxal (PL)
  4. pyridoxal 5'-phosphate (PLP)
  5. pyridoxamine (PM)
  6. pyridoxamine 5'-phosphate (PMP)
  7. 4-pyridoxic acid (PA)

The reasons for these differences in information about vitamin B6 include:

  • the level of detail e.g. some introductory textbooks deliberately include only short simple descriptions
  • the type and amount of knowledge that is assumed i.e. advanced biochemistry textbooks assume knowledge that school textbooks explain if readers need to understand it
  • the purpose and context of the description or article e.g. scientific papers sometimes state elementary definitions and explain accepted theories - but only if they are pertinent to the investigations conducted or explanations offered.

Details about the biochemistry of vitamin B6 are not usually required for first-level courses in human biology, diet and nutrition, and related health science subjects. However, students whose understanding of organic chemistry enables them to follow descriptions of the reactions of vitamin B6 might find them interesting.

Active Form of Vitamin B6:

The three main forms of vitamin B6 (i.e. pyridoxine, pyridoxal and pyridoxamine) can be converted to the biochemical pyridoxal phosphate which is sometimes written pyridoxal 5'-phosphate and abbreviated to 'PLP'. This is a cofactor in many reactions of amino acid metabolism, including transamination, deamination, and decarboxylation.

This information is useful to people who also need to understand the chemical reactions within the body, i.e. specific details about metabolism.

Functions of Vitamin B6:

Vitamin B6 has many functions, of which the main functions of vitamin B6 are:

  • Helps with conversion of foods into energy via working with enzymes
  • Promotion of healthy skin, teeth, and gums and nerves.
  • Formation of red blood cells
  • Formation of hormones involved in the functioning of the brain e.g. serotonin and melatonin, which affect mood and the sleep cycle.
  • Balancing of hormones involved in the female menstrual cycle, hence vitamin B6 is sometimes used to help alleviate the symptoms of premenstrual syndrome (PMS) and the menopause.
  • Synthesis & breakdown of amino acids
  • Supports the immune system, hence the body's resistance to disease
  • Vitamin B6 is needed in order for vitamin B12 to be absorbed by the body.

Examples of some functions of vitamin B6 in metabolic processes i.e. biochemical reactions:

  • Pyridoxal phosphate is a coenzyme for many enzymes. (A coenzyme is a substance that works with an enzyme to initiate or assist the function of the enzyme; coenzymes cannot operate alone but need the presence of an enzyme to have an effect.)
  • Conversion of the amino acid tryptophan to niacin (which is also known as vitamin B3). Hence deficiency of vitamin B6 can lead to 'secondary pellagra', pellagra being an undernutrition disease associated with deficiency of vitamin B3 - symptoms include scaly dermatitis on exposed surfaces of skin, diarrhea and depression.
  • Involved in the synthesis of haem - plays an important role because pyridoxal phosphate (PLP) is an essential cofactor in the synthesis of aminolevulinic acid (ALA), which is the rate-limiting step of haem synthesis.
  • Important for amino acid metabolism

Sources of Vitamin B6:

Many foods include some vitamin B6.

Examples of sources of vitamin B6 include:

  • Whole grains (wheat or corn) e.g. whole-grain cereals
  • Wheatgerm
  • Wholemeal bread
  • Meat incl. poultry (e.g. chicken) and liver
  • Fish
  • Milk
  • Nuts
  • Bananas
  • Green vegetables, e.g. brussel sprouts
  • Potatoes
  • Baked beans

Vitamin B6 is easily destroyed by food storage and food processing, such as cooking.

Sufficient on-going intake of vitamin B6 is important because excess vitamin B6 is excreted from the body in urine - as opposed to being stored for later use.

Problems due to insufficient or too much Vitamin B6:

Signs of Deficiencies of Vitamin B6

Signs of Excessive Intake of Vitamin B6

Dietary deficiency of vitamin B6 is rare, but can lead to:

  • Loss of appetite
  • Hypochromic, microcytic anaemia
  • (secondary) pellagra
  • Fatigue
  • Nervousness
  • Insomnia
  • Convulsions
  • Depression
  • Memory problems
  • Menstrual problems

Toxic effects of vitamin B6 are rare. Even so, intake of high doses of vitamin B6 over an extended period of time has been associated with development of sensory neuropathy, i.e. damage to the body's sensory nerves. An example of an effect of this is the sensation of 'pins and needles'.

As also applies to many other dietary supplements, vitamin B6 should not be taken on its own without expert supervision. In some rare cases it may interfere with prescribed medication and so should be discussed with any professionals who are prescribing medication for the person, e.g. levodopa (for Parkinson's disease).

See also vitamins, minerals, amino acids, what is a balanced diet? and the health benefits of drinking water.

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