Vitamin B6 – Pyridoxine
- in the metabolism of proteins, fats, and carbohydrates;
- to make hormones and neurotransmitters;
- to support the immune system.
It also plays a role in the production of normal, healthy red blood cells and some of the neurotransmitters needed for proper nervous system function. In conjunction with folic acid and cobalamin, it acts to reduce homocysteine levels, thus lowering the risk of developing heart disease.
Mild deficiencies of pyridoxine are common, despite the low daily requirements. The Recommended Daily Allowance (RDA) is:
- for babies under 6 months of age – 0.1 mg
- for babies 6 months to 1 year old – 0.3 mg
- for children 1 to 3 years old – 0.5 mg
- for children 4 to 8 years old – 0.6 mg
- for children 9 to 13 years old – 1 mg
- for males aged 14–18 years – 1 mg
- for males 19 years and older – 1.3 mg
- for females aged 14–18 years – 1.2 mg
- for females over the age of 19 – 1.3 mg
- for prenant females – 1.9 mg
- for lactating females – 2 mg.
Pyridoxine has numerous therapeutic uses apart from treating deficiency. It has a calming effect on the nervous system and may alleviate insomnia by increasing serotonin levels in the brain.
Because of the calming effects of pyridoxine, it has been tried as a possible adjunctive treatment for schizophrenia. The findings, however, were inconclusive. Evidence suggests that pyridoxine reduces nausea for about a third of pregnant women who experience morning sickness. In addition, pyridoxine does not have any harmful effects on the fetus.
Pyridoxine is also used to decrease the risk of heart disease by lowering homocysteine levels. Taken in conjunction with magnesium supplements, pyridoxine has been found to have beneficial effects on some people with autism. The vitamin B6 and magnesium combination can also help to prevent the recurrence of calcium oxalate kidney stones in susceptible people. Those who are affected by depression or gestational diabetes may benefit from a moderate addition of it, as well.
One type of hereditary anemia and several metabolic diseases are effectively treated with high doses of pyridoxine.
A few chemotherapeutic agents, including vincristine, can be taken with fewer side effects when pyridoxine is added to the patient’s regimen.
The data are equivocal on whether asthma is improved by vitamin B6 supplementation, but high doses—50 mg, taken twice daily—were used in the studies performed, creating a risk of nerve injury.
There is some question as to the benefit to taking it for PMS, carpal tunnel syndrome, or diabetic neuropathy, although there is no harm in a trial of additional B6 at a modest level.
Taking B6 has some benefit for those suffering from osteoporosis and epilepsy. Nevertheless, the advice of a healthcare professional should be sought before undertaking this, and any, supplemental treatment.
Meats are the best food source of pyridoxine, followed by dairy and eggs. Although some grains contain B vitamins, they are generally lost in processing. Bananas, potatoes, mangoes, and avocados have the highest vitamin B6 value among vegetarian foods.
Fresh foods should be used because freezing destroys much of this vitamin. Minimizing the amount of water used in cooking prevents pyridoxine and other water soluble vitamins from leaching into it.
Pyridoxine supplements are available in both oral and injectable forms. Pyridoxine is also added to many processed grain products. Individuals may consider taking a balanced B complex supplement rather than high doses of an individual vitamin unless given instructions by a medical doctor to do so. Supplements ought to be stored in a cool, dry place, away from light, and out of the reach of children.
Symptoms of pyridoxine deficiency are nonspecific but may include nervousness, irritability, muscle twitches, insomnia, confusion, weakness, loss of coordination, and anemia. Frequent infections are likely as well due to the importance of vitamin B6 to the immune system.
Risk factors for deficiency
Since meats are the best source of pyridoxine, followed by dairy and eggs, vegans are one of the groups at risk for deficiency. A balanced B vitamin supplement is adequate to prevent deficiency. People with malabsorption syndromes, chronic illnesses, or hyperthyroidism may require somewhat larger amounts of vitamin B6. Those who take birth control pills are more likely to have abnormally low levels and may benefit from a supplement of 25–50 mg per day.
Elderly people are more likely to have a poor diet, and deficient pyridoxine will both increase their susceptibility to illness and prolong recovery.
Alcoholics, smokers, and people who take certain medications, including estrogen, theophylline (for asthma), hydralazine (for hypertension), penicillamine (for rheumatoid arthritis), and isoniazid (for tuberculosis) are more likely to need extra pyridoxine.
For asthmatics on theophylline, the side effects of this medication can also be reduced by the additional vitamin B6.
Allergic reactions to oral or injected pyridoxine are known to occur but are rare. It is possible to have toxic effects from large doses.
At 2,000 mg daily, nerve damage may occur, causing numbness or tingling of the extremities and loss of coordination. These symptoms are usually, but not always, reversible.
At 500 mg for daily dosages, there is possible toxicity if chronically taken many months or years.
Finally, at 150 mg taken daily, there is rare, but possible, toxicity with long-term use.
Thus, it is best to take no more than 50 mg a day unless under medical supervision to avoid the potential for toxicity. Chronic large doses may also cause photosensitivity.
Pregnant women who take megadoses may create dependence in the newborn, who would be at risk for seizures. Nursing infants can also suffer adverse effects from large doses ingested in breast milk.
High doses of pyridoxine may cause a rash in addition to the more serious complications listed under ‘‘Precautions.’’
Optimal levels of riboflavin, vitamin C, magnesium, and selenium improve pyridoxine absorption. The effectiveness of levodopa is reduced by pyridoxine. Anyone taking levodopa, most commonly used to treat Parkinson’s disease, should not take supplemental vitamin B6. Other combination forms of medication for Parkinson’s disease may not be affected.
Phenytoin and phenobarbital, two medications sometimes used to control epilepsy, may also become less effective in the presence of extra vitamin B6. Pyridoxine requirements are increased by the medications hydralazine, penicillamine, isoniazid, and some immunosuppressive agents. Both theophylline and estrogen containing medications, including birth control pills, block the metabolism of pyridoxine.