Vitamin B6: Dietary Source, RDA, and Functions

Vitamin B6 is an essential water-soluble vitamin widespread among various food groups such as yeasts, cereals, and the liver.

Alternate name	Pyridoxine
Year of Discovery	1934
Discovered by	Paul Gyorgy

Vitamin B6 is the generic term applied to a family of three related pyridine derivatives; pyridoxine (alcohol), pyridoxal (aldehyde), pyridoxamine and their respective 5’-phosphatase forms (PLP, PMP, and PNP).

The active form of vitamin B6, Pyridoxal 5’ phosphate (PLP), assists more than 100 enzymes in performing various functions, including carbohydrate, fat, and protein metabolism. PLP maintains normal levels of homocysteine level and supports immune function and brain health. 

Dietary Sources

Vitamin B6 is found in many foodstuffs, mainly in meat, legumes, and nuts. Many vegetables, fruits, and whole grains are good sources of vitamin B6.

In dietary supplements, vitamin B6 is usually available in the form of pyridoxine. Vitamin B6-fortified ready-to-eat breakfast cereals are also available in the marketplace. Most multivitamin-mineral supplements contain vitamin B6.

Rich sources of vitamin B6 include;

1. Meat
2. Poultry
3. Turkey
4. Fish (most)
5. Egg
6. Liver
7. Nuts and seeds
8. Potatoes and sweet potatoes
9. Legumes (pulses)
10. Tofu and other soy products
11. Non-citrus fruits such as bananas and watermelons
12. Whole-grain (wheat) and fortified cereals
13. Green leafy vegetables

Recommended Dietary Allowance

The RDA for vitamin B6 for young adults is 1.3 mg/day. The requirement is increased to 2.0 mg/day during pregnancy and lactation.[1] Vitamin B6 requirements are related to protein intake and not to calorie intake.

Life Stage Group	Vitamin B6 (mg/day)
Infants (mo)
0-6 months	0.1* mg/day
7-12 months	0.3* mg/day
Children
1-3 years	0.5 mg/day
4-8 years	0.6 mg/day
Males
9-13 years	1.0 mg/day
14-50 years	1.3 mg/day
>51 years	1.7 mg/day
Females
9-13 years	1.0 mg/day
14-50 years	1.3 mg/day
>51 years	1.5 mg/day
Pregnant girl or woman	1.9 mg/day
Lactating mother	2.0 mg/day

* Adequate Intake (AI)

The critical adverse effect of a high intake of vitamin B6 is sensory neuropathy. The tolerable upper intake level (UL) of vitamin B6 for adults is 100 mg/day.

Absorption and Excretion

Pyridoxal phosphate (PLP) is the main dietary form of vitamin B6. PLP undergoes phosphatase-mediated hydrolysis to pyridoxal (PL), crosses the enterocyte, and enters the bloodstream. In the liver, PL is converted back to PLP by the enzyme pyridoxal kinase. PLP is the primary circulating form of vitamin B6.

Skeletal muscle is the major source of PLP in the body. At least 80% of the vitamin B6 pool in the body is stored in muscle as pyridoxal 5′-phosphate (PLP) bound to glycogen phosphorylase. Products of vitamin B6 metabolism are excreted in the urine in the form of 4-pyridoxic acid.

Functions

Vitamin B6, in the form of PLP, is a coenzyme for >100 enzymes involved in amino acid metabolism. PLP is a coenzyme for aminotransferases, decarboxylases, and dehydratases. PLP is a coenzyme in the first step of heme biosynthesis and homocysteine transsulfuration to cysteine.

The major functions of vitamin B6 are;

• Reducing the risk of cardiovascular disease by aiding to lower homocysteine levels
• Helping to convert tryptophan to niacin and serotonin, a neurotransmitter that plays critical roles in sleep, appetite, and mood
• Helping make red blood cells
• Influencing cognitive abilities and immune function

Deficiency

Vitamin B6 status can be measured with plasma PLP level. A plasma PLP of <20 nmol/L indicates a vitamin B6 deficiency. Vitamin B6 deficiency is rare in healthy individuals, but a certain group has more risk of having vitamin B6 deficiency. These are;

• People who are on kidney dialysis or had a kidney transplant,
• People with autoimmune disorders. For example, people with inflammatory bowel disease, Crohn’s disease, celiac disease, ulcerative colitis, and rheumatoid arthritis.
• People with alcohol dependence.

Symptoms of vitamin B6 deficiency include seborrheic dermatitis, microcytic anemia, convulsions, and confusion. Microcytic anemia occurs due to PLP’s role as a cofactor in the first step in heme biosynthesis.