Vitamin B6

Vitamin B₆ (Pyridoxal 5 Phosphate)

Vitamin B₆ is a water-soluble vitamin or essential nutrient found naturally in various foods and added to foods and supplements. Pyridoxal 5′-phosphate (PLP) is the active form of vitamin B₆. Pyridoxine hydrochloride is the form of B₆ that is most commonly used as a dietary supplement due to its chemical stability. PLP is a coenzyme or vitamer for many enzymes that use for the synthesis of hemoglobin and controls the metabolism of amino acids, glucose, and lipids. The phosphate form is inconvertible in our bodies. Vitamin B₆ is beneficial for the development of the nervous system and the metabolism of protein, carbohydrates, and fats. Therefore, B₆ uses mainly for turning food into energy and helps to create neurotransmitters.

Chemically, B₆ vitamers are derivatives of 2-methyl-3-hydroxy-5-hydroxymethyl-pyridine where a C4 position can substitute by a hydroxymethyl group in pyridoxine, an aminomethyl group in pyridoxamine, and an aldehyde group in pyridoxal.

The alcohol group present in the 5′ positions can be esterified to phosphate to form pyridoxine 5′-phosphate (PNP), pyridoxamine 5′-phosphate (PMP), and pyridoxal 5′-phosphate (PLP).

Sources of vitamin B₆

The main sources of vitamin B₆ for humans are the diet. It can be found in a variety of animal and plant foods.

• Beef liver
• Yellowfin tuna
• Salmon
• Fortified cereals
• Chickpeas
• Bulgur
• Cottage cheese
• Roasted chicken breast
• Poultry
• Potatoes
• Banana

Some vegetables and fruits, dark leafy greens, bananas, papayas, oranges, and cantaloupe contain principally pyridoxine and its phosphate and glucoside forms of B₆. In meat and fish, B₆ is mainly present as PLP and PMP.

The average vitamin B₆ content of human milk is low in early childbirth. High-performance liquid chromatography analysis indicates that B₆ in human milk contains pyridoxal, pyridoxal-5-phosphate, pyridoxamine, and pyridoxamine-5′-phosphate. The supplementation of mothers with 2.5 or 15 mg of pyridoxine gives similar distribution patterns for the vitamers in milk.

Vitamin B₆ recommended daily intake

Like other B vitamins, our body does not store B₆ and releases any excess in urine. Therefore, people need to get enough vitamin B₆ reached foods or supplements every day.

The daily requirement for B₆ depends on several factors because B₆ controls various biological reactions of a person. The recommended daily dietary allowances (RDA) for vitamin B₆ are,

Vitamin B₆ supplement

Vitamin B₆ supplements are available in capsule or tablet form to treat B₆ deficiency. Pyridoxine hydrochloride is available as a licensed drug or supplement for oral administration in most Western countries. It is converted to pyridoxamine 5′-phosphate (PMP) by the enzyme pyridoxal kinase.

The metabolically active form of B₆ (pyridoxal 5′-phosphate) may be obtained by the enzymes pyridoxamine-phosphate transaminase or pyridoxine 5′-phosphate oxidase. The activity of the enzyme pyridoxine 5′-phosphate oxidase is dependent on flavin mononucleotide (FMN). FMN is a cofactor produced from riboflavin (vitamin B₂).

Most people of all ages in developed counties consume sufficient B₆ and do not require supplements. Those who are more likely to have low levels of B₆ and required supplementation may include:

• people who drink excess alcohol
• people with obesity
• during pregnancy or breastfeeding periods

Functions of vitamin B₆

Functions in metabolism

The metabolism of protein, carbohydrates, and fats is the main function of vitamin B₆.

• In protein metabolism, B₆ helps to regulate the balance of amino acids in the body.
• PLP undergoes a condensation reaction with the amino group of amino acids to produce a Schiff base. It forms the basis of most of the enzyme-catalyzed reactions for which PLP is required.
• Pyridoxal 5′-phosphate is a coenzyme that is involved in glycogenolysis of the body. It enables the breakdown of glycogen into glucose for energy production. Glycogenolysis is primarily found in muscle, liver, and brain.
• PLP is one of the B₆ vitamers which are required for the normal metabolism of fats and essential fatty acids. It is an essential component of enzymes that facilitate the biosynthesis of sphingolipids. For example, the synthesis of ceramide requires PLP.
• Selenomethionine is the primary dietary supplement for selenium. The cofactor PLP is used to activate enzymes that allow selenium to be used from the dietary form.

Functions in hemoglobin synthesis

Heme is an iron-binding prosthetic group in metalloproteins. Its function in hemoglobin is to bind and transport oxygen from the lungs to the tissues.

The biosynthesis of hemoglobin depends on the activity of the enzyme aminolevulinic acid synthase. PLP serves as a coenzyme for the enzyme aminolevulinic acid synthase.

Neurotransmitters

Vitamin B₆ (Pyridoxal 5′-phosphate) is a coenzyme that helps in the biosynthesis of five important neurotransmitters. These are serotonin, dopamine, epinephrine, norepinephrine, and gamma-aminobutyric acid. These are important chemical messengers that help regulate energy in our brains.

Gene expression

A recent study suggests that vitamin B₆ has modulated gene expression not only for steroid hormone-responsive or PLP-dependent enzymes but also for steroid- and PLP-unrelated proteins such as serum albumin. PLP has been implicated in increasing or decreasing the expression of certain types of genes.

Albumin gene expression by B₆ goes through a novel mechanism. It involves the inactivation of tissue-specific transcription factors, such as HNF-1 or C/EBP.

Vitamin B₆ in fertility

• B₆ can raise the levels of progesterone hormone that makes the body ready for pregnancy.
• Vitamin B₆ helps in the production of cervical mucus that transports the sperm to reach the egg.
• The menstrual cycle for women consists of two phases – the follicular phase and the luteal phase. The luteal phase of the menstrual cycle is strengthened by B₆. It makes the uterus more receptive and increases the chance of pregnancy.
• It can increase or restore libido. Hence B₆ may increase the sexuality of men and women.

Uses of vitamin B₆

Plants synthesize pyridoxine to protect from the ultraviolet-B radiation of sunlight. Pyridoxine also participates in the synthesis of chlorophyll.

Animals cannot synthesize any of the various forms of vitamin B₆. Therefore, they must obtain B₆ via diet, either of plants or other animals.

• Vitamin B₆ plays an important role in protein, carbohydrates, and fats metabolism.
• It also participates in the production of neurotransmitters, hemoglobin, and the formation of nicotinic acid. Therefore, vitamin B₆ is vital for maintaining a healthy nervous system, skin, muscles, and blood.
• Vitamin B₆ supplementation may help in mild symptoms of morning sickness, nausea, and vomiting during pregnancy.
• B₆ may help to protect us from the harmful effects of air pollution by reducing the impact of pollution on the epigenome.
• The forms of vitamin B₆, pure crystalline pyridoxine powder, or pyridoxine hydrochloride supplements are used in amino acid metabolism and maintain healthy or oily skin.

Benefits of vitamin B₆

B₆ is a vitamin that is beneficial for our central nervous system and the metabolism of the human body. PLP is the only B₆ vitamer that assists more than 100 enzymes in performing various biological functions.

• It benefits brain development during pregnancy and infancy.
• B₆ creates neurotransmitters, including serotonin and dopamine.
• It creates hemoglobin which is the part of red blood cells that carries oxygen in human bodies.
• It helps to regulate the balance of amino acids in our body.
• B₆ is also closely involved in hormone synthesis.

Vitamin B₆ and weight loss

B₆ plays a crucial role in metabolizing protein, fats, and carbohydrates in our bodies. In presence of B₆, our metabolism speeds up and allows us to burn calories and lose weight quicker.

Vitamin B₆ deficiency

Deficiencies of vitamin B₆ are uncommon in the United States and other developed counties. The deficiency of B₆ may happen if a person has poor intestinal absorption or takes some medicines. The deficiencies of B₆ may cause low levels of other B vitamins, such as vitamin B₁₂ and folic acid (folate).

The main signs and symptoms of a B₆ deficiency may include:

• Tingling, numbness, and pain in the hands and feet (peripheral neuropathy)
• Anemia
• Seizures
• Weakened immune system
• Depression
• Confusion
• Seborrheic dermatitis
• Inflammation of the tongue, or glossitis
• Inflammation and cracking of the lips

The vitamin B₆ level is decreased for women with type 1 diabetes and patients with systemic inflammation, liver disease, rheumatoid arthritis, and infected with HIV.

Diagnosis of B₆ deficiency is usually clinical and measurement of serum pyridoxal phosphate is most common to measure B₆ deficiency. There is no single accepted laboratory test to measure the B₆ level.

Other useful methods to measure vitamin B₆ levels may include UV spectrometry, spectrofluorimetry, mass spectrometry, thin-layer chromatography, high-performance liquid chromatography, electrochemical, and enzymatic methods.