• Vitamin B₆ is the term for three related compounds, pyridoxine, pyridoxal and pyridoxamine and their phosphorylated derivatives which are pyridoxine 5'-phosphate, pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate. Vitamin B6 technically refers to all six of these compounds, although vitamin B6 is used interchangeably with pyridoxine. Vitamin B₆ technically refers to all six of these vitamers, although vitamin B₆ is used interchangeably with pyridoxine.
• Pyridoxine, pyridoxine 5'-phosphate and pyridoxine glucosides are found in plant foods. The other vitamers, primarily pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate, are found in animal products.
• Glycosylated pyridoxine forms of vitamin B₆ range from 5 to 75% of the total vitamin B₆ content in fruits, vegetables and grains. There is very little or none of the glycosylated pyridoxine form of vitamin B₆ in animal products.
• Vitamin B₆ is soluble in water and stable to heat and acid. However, oxidation and exposure to alkali and UV light destroy vitamin B₆.
• As much as 50% of vitamin B₆ is destroyed during cooking and processing.

• The coenzyme pyridoxal 5'-phosphate is involved in a wide range of biochemical reactions. These include the metabolism of glycogen and amino acids, the synthesis of nucleic acids, and the synthesis and metabolism of hemoglobin. It is also involved in the synthesis of sphingomyelin and other sphingolipids and neurotransmitters (serotonin, dopamine, norepinephrine, histamine and gamma-aminobutyric acid.)
• Pyridoxal 5'-phosphate is involved in the metabolism of gamma-aminobutyric acid, a major inhibitory neurotransmitter in the central nervous system.
• Vitamin B₆ in the form of pyridoxal 5'-phosphate acts as a coenzyme for more than 100 enzymes.

• The signs and symptoms of vitamin B₆ deficiency are microcytic, hypochromic anemia, seizure activity, seborrheic dermatitis, confusion and depression.
• Deficiency of vitamin B₆ in children and infants results in electroencephalogram abnormalities and seizure activity.
• Deficiency of vitamin B₆ in adults results in cheilosis, glossitis, stomatitis, anemia, irritability, confusion and depression.
• Secondary deficiencies of vitamin B₆ may result from malabsorption, uremia, cancer, heart failure, and cirrhosis. Pregnant adolescent females, the elderly, and alcoholics are populations at risk for secondary vitamin B₆deficiency.
• Other vitamin B₆ deficiencies may result from chemical inactivation, excessive vitamin B₆ loss, or increased metabolic activity associated with the use of some medications (e.g., isonicotinic acid hydrazide, penicillamine, cycloserine, thionamide, hydralazine and theophylline).

• Infants who are breastfed and are born with low plasma concentrations of vitamin B₆ may be at risk for vitamin B₆ deficiency.
• The elderly, who have a poor intake of vitamin B₆, may have accelerated hydrolysis of pyridoxal phosphate and oxidation of pyridoxal to pyridoxic acid. Additionally, in one study on healthy individuals aged 65 years or older, researchers found abnormal concentrations of B6 and riboflavin. They concluded that a high proportion of older adults might have suboptimal status for these nutrients (B6 and riboflavin) even when the recommended nutrient intakes are achieved through diet.⁹
• Alcoholics may be at risk due to the impaired conversions of pyridoxine and pyridoxamine to pyridoxal phosphate.
• Maintenance dialysis causes an abnormal loss of vitamin B₆, increasing the risk of vitamin B₆ deficiency for renal patients.
• Individuals on a variety of drug therapies that inhibit activity of the vitamin, primarily isonazid, penicillamine, corticosteriods, and or anti-convulsants, may be at risk for vitamin B₆ deficiency.
• Vitamin B₆ enzyme is defective in seven inborn errors of metabolism. The enzyme has a defect in the pyridoxal 5'-phosphate binding site. These disorders may be responsive to high doses of vitamin B6.

• Infants
  1. 0-6 months, 0.1 mg/day
  2. 7-12 months, 0.3 mg/day
• Children
  1. 1-3 years, 0.5 mg/day
  2. 4-8 years, 0.6 mg/day
• Males
  1. 9-13 years, 1.0 mg/day
  2. 14-50 years, 1.3 mg/day
  3. 51 and older, 1.7 mg/day
• Females
  1. 9-13 years, 1.0 mg/day
  2. 14-18 years, 1.2 mg/day
  3. 19-50 years, 1.3 mg/day
  4. 51 and older, 1.5 mg/day
• Pregnancy
  1. 18 years and younger, 1.9 mg/day
  2. 19 years and older, 1.9 mg/day
• Lactation
  1. 18 years and younger, 2.0 mg/day
  2. 19 years and older, 2.0 mg/day

Tolerable Upper Intake Levels

• Children
  1. 1-3 years, 30 mg/day
  2. 4-8 years, 40 mg/day
• Males, Females
  1. 9-13 years, 60 mg/day
  2. 14-18 years, 80 mg/day
  3. 19 and older, 100 mg/day
• Pregnancy and Lactation
  1. 18 years and younger, 80 mg/day
  2. 19 years and older, 100 mg/day

• Many antibiotics can destroy normal gastrointestinal flora leading to decreased production of the B vitamins in general. The clinical significance is unknown.
• Excessive alcohol consumption may increase the requirement for pyridoxine.
• Isoniazid (INH), an antituberculosis drug, can increase pyridoxine requirements. Patients receiving more than 10mg/kg/day of INH should be supplemented with 50-100mg of pyridoxine per day to prevent peripheral neuritis. It is suggested that children receiving the medication do not need vitamin B6 supplementation unless they have nutritional deficiencies. It is recommended that children or adolescents with low meat and milk diets, symptomatic children with HIV infection, breastfeeding infants and women, and pregnant women take supplementation.
• Cycloserine, an antibiotic used mainly for tuberculosis, can block the actions of pyridoxine and increase renal excretion of the vitamin leading to anemia or peripheral neuritis. Vitamin B6 supplementation may be required in some patients receiving cycloserine.
• The therapeutic effects of levodopa, an anti-Parkinsonian agent, can be compromised pyridoxine due to accelerated peripheral metabolism of the drug. Concomitant use of carbidopa with levodopa prevents the increase in this metabolism by pyridoxine. Patients using levodopa alone should not use pyridoxine in doses greater than 5 mg/day.
• Pyridixine has been shown to decrease serum concentrations of anticonvulsant medications, such as phenobarbital and phenytoin. Supplementation is not advised without first consulting with a physician or pharmacist.
• Penicillamine, used for rheumatoid arthritis or Wilson’s disease, can increase pyridoxine requirements.
• Neurotoxicity from the chemotherapeutic drugs, altretamine or cisplatin can be reduced with pyridoxine; however, pyridoxine may compromise therapeutic benefits of the drugs and should not be administered with altretamine and/or cisplatin.