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Vitamin B6 is a vitamin that exists in three forms: pyridoxine,
pyridoxal, and pyridoxamine. It is involved in many functions
including maintenance of a healthy immune system, proper function of
the nervous system, and the oxygen-carrying capacity of red blood
cells. Meat, fish, beans, and fortified cereals are good sources of
dietary vitamin B6. The Recommended Daily Allowance of vitamin B6 is
1.3-1.9 mg in adult men and 1.3-1.5 mg in adult women. A vitamin B6
deficiency usually does not produce symptoms, and supplementation can
be used if dietary intake is inadequate. The effectiveness of the
nutrient in the treatment of neurological diseases, cardiovascular
disease, carpal tunnel syndrome, and premenstrual syndrome is being
researched but has not been proven scientifically.

Contents
--------

1. How Vitamin B6 Works

1. Sources

2.1 Dietary sources of vitamin B6

1. Benefits

3.1 Neurological disease and neuropathy

3.2 Carpal tunnel syndrome

3.3 Premenstrual syndrome

3.4 Morning sickness

3.5 Autism

1. Recommended Daily Intake

4.1 Recommended daily allowance for vitamin B6 in adults

4.2 Vitamin B6 deficiency

4.2.1 Risk factors

4.3 Too much vitamin B6

1. Side Effects

1. Risks

6.1 Interactions

1. Research

7.1 Vitamin B6, homocysteine, and heart disease

1. History

8.1 How vitamin B6 was discovered

1. References

10 External Links

How Vitamin B6 Works
--------------------

Vitamin B6

Vitamin B6 is a water-soluble vitamin that exists in three major
chemical forms: pyridoxine, pyridoxal, and pyridoxamine. It has many
physiological functions and is vital for good health. Over 100 enzymes
use vitamin B6 to help in the metabolism of proteins. Several other
functions of vitamin B6 are:

Metabolism of red blood cells

Immune system function

Nervous system function

Conversion of the amino acid tryptophan to the vitamin niacin

Hemoglobin in red blood cells carries oxygen to tissues. Vitamin B6 is
needed to make hemoglobin. Vitamin B6 also helps increase the amount
of oxygen carried by hemoglobin. A form of anemia can result if
vitamin B6 is deficient.

White blood cells, or lymphocytes, help fight infection. Their
activation and proliferation are essential to a healthy immune
response directed towards foreign pathogens. Through its involvement
in protein metabolism and cellular growth, vitamin B6 is important to
the immune system. It helps maintain the health of lymphoid organs (thymus,
spleen, and lymph nodes) that make white blood cells. Animal studies
show that a vitamin B6 deficiency decreases the production of
antibodies by white blood cells and suppresses the immune response.

Vitamin B6 also helps maintain blood glucose (sugar) levels within the
normal range. When caloric intake is low, the body maintains glucose
by converting stored carbohydrate or other nutrients into glucose. A
shortage of vitamin B6 will limit these processes, but supplements of
this vitamin do not enhance them in well-nourished individuals.

Sources
-------

Vitamin B6 is found in a wide variety of foods including fortified
cereals, meat (e.g., poultry, pork), fish (e.g., tuna, salmon), beans,
peanut butter, and some fruits and vegetables. The following is a list
of some dietary sources of vitamin B6:

Dietary sources of vitamin B6

Food

Milligrams (mg)
per serving

% DV

Ready-to-eat cereal, 100% fortified, ¾ c

2.00

100

Potato, Baked, flesh and skin, 1 medium

0.70

35

Banana, raw, 1 medium

0.68

34

Garbanzo beans, canned, ½ c

0.57

30

Chicken breast, meat only, cooked, ½ breast

0.52

25

Ready-to-eat cereal, 25% fortified, ¾ c

0.50

25

Oatmeal, instant, fortified, 1 packet

0.42

20

Pork loin, lean only, cooked, 3 oz

0.42

20

Roast beef, eye of round, lean only, cooked, 3 oz

0.32

15

Trout, rainbow, cooked, 3 oz

0.29

15

Sunflower seeds, kernels, dry roasted, 1 oz

0.23

10

Spinach, frozen, cooked, ½ c

0.14

8

Tomato juice, canned, 6 oz

0.20

10

Avocado, raw, sliced, ½ cup

0.20

10

Salmon, Sockeye, cooked, 3 oz

0.19

10

Tuna, canned in water, drained solids, 3 oz

0.18

10

Wheat bran, crude or unprocessed, ¼ c

0.18

10

Peanut butter, smooth, 2 Tbs.

0.15

8

Walnuts, English/Persian, 1 oz

0.15

8

Soybeans, green, boiled, drained, ½ c

0.05

2

Lima beans, frozen, cooked, drained, ½ c

0.10

6

 DV = Daily Value. DVs are reference numbers based on the Recommended
Dietary Allowance (RDA). They were developed to help consumers
determine if a food contains a lot or a little of a specific nutrient.
The DV for vitamin B6 is 2.0 milligrams (mg). The percent DV (%DV)
listed on the nutrition facts panel of food labels tells you what
percentage of the DV is provided in one serving. Percent DVs are based
on a 2,000 calorie diet. Your Daily Values may be higher or lower
depending on your calorie needs. Foods that provide lower percentages
of the DV also contribute to a healthful diet.

The 2005 Dietary Guidelines for Americans suggest that nutrients such
as vitamin B6 should be obtained through diet because foods contain a
variety of vitamins, minerals, proteins, and other substances that are
beneficial to health. It states that supplements may be considered if
a diet lacks the recommended allowance of any vitamin or mineral.

Benefits
--------

Bananas, a source of Vitamin B6. Source: FreeDigitalPhotos.net

Vitamin B6 supplementation may have a role in the prevention or
treatment of a variety of neurological disorders. But data supporting
the therapeutic role of the nutrient are not always convincing and
sometimes, as is the case with carpal tunnel syndrome and premenstrual
syndrome, are lacking altogether.

Neurological disease and neuropathy

Vitamin B6 is needed for the synthesis of neurotransmitters, which are
the chemicals that transmit signals between cells. Neurotransmitters
cause neurons to fire in the brain and activate muscles. The
neurotransmitters dopamine and serotonin are necessary for the brain
to function properly. Researchers are investigating the relationship
between vitamin B6 status and a wide variety of neurologic conditions
such as seizures, depression, chronic pain, Parkinson's disease, and
headache. Depression and headache, for example, are characterized by
low levels of neurotransmitters in the brain. Vitamin B6 may help
boost serotonin levels in persons with depression, much like the
effects of some antidepressants. So far, however, vitamin B6
supplements have not proved effective for treatment of either
depression or migraine headaches. One study found that a placebo was
as effective as vitamin B6 headaches and depression associated with
use of low dose oral contraceptives.

Alcohol abuse can result in neuropathy, abnormal nerve sensations in
the arms and legs. This neuropathy is often caused by a poor diet, and
dietary supplements that include vitamin B6 may prevent or decrease
its incidence.

Carpal tunnel syndrome

Vitamin B6 was first recommended for carpal tunnel syndrome almost 30
years ago. Several popular books still recommend taking 100 to 200
milligrams of vitamin B6 daily to treat the condition, even though
scientific studies do not indicate it is effective. The Institute of
Medicine recently established an upper tolerable limit for vitamin B6
of 100 mg per day for adults. Cases of neuropathy have been reported
following treatment with excessive vitamin B6 for carpal tunnel
syndrome.

Premenstrual syndrome

Vitamin B6 has become a popular remedy for treating the discomforts
associated with premenstrual syndrome (PMS). Much like with other
conditions however, the effectiveness of vitamin B6 supplementation
for the relief of symptoms related with PMS has not been shown in
clinical trials. One study indicated that a placebo was as likely to
relieve symptoms of PMS as was vitamin B6. In addition, vitamin B6
toxicity has been seen in increasing numbers of women taking vitamin
B6 supplements for PMS. One review showed that 23 of 58 women had
neuropathy while taking daily vitamin B6 supplements for PMS. In these
women, blood levels of B6 were above normal. No scientific evidence
supports a role for vitamin B6 in the treatment of PMS.

Morning sickness

Many women use vitamin B6 to treat morning sickness during pregnancy.1
Studies proving its effectiveness have not been performed.

Autism

Several studies have shown a benefit of vitamin B6 use in patients
with autism.2

Recommended Daily Intake
------------------------

The Recommended Dietary Allowance (RDA) is the average daily dietary
intake level that is sufficient to meet the nutrient requirements of
nearly all (97 to 98 percent) healthy individuals in each life-stage
and gender group.

Recommended daily allowance for vitamin B6 in adults

Life-Stage

Men

Women

Pregnancy

Lactation

Ages 19-50

1.3 mg

1.3 mg

Ages 51+

1.7 mg

1.5 mg

All Ages

1.9 mg

2.0 mg

Results of two national surveys, the National Health and Nutrition
Examination Survey (NHANES III 1988-94), and the Continuing Survey of
Food Intakes by Individuals (1994-96 CSFII), indicated that diets of
most Americans meet current intake recommendations for vitamin B6.

Vitamin B6 deficiency

Symptoms of vitamin B6 deficiency are rare in the United States. Many
elderly Americans, however, have low blood levels of vitamin B6. This
suggests suboptimal vitamin B6 nutritional status. Vitamin B6
deficiency can occur in individuals with poor diets that are deficient
in many nutrients. Symptoms of a vitamin B6 deficiency occur after
intake has been very low for an extended time. Below are some symptoms
of Vitamin B6 deficiency:

Dermatitis (skin inflammation)

Confusion

Convulsions

Depression

Glossitis (a sore tongue)

Anemia

These symptoms can be caused by a variety of conditions and diseases.
Therefore, a physician should be consulted to determine the cause and
initiate appropriate treatments.

Risk factors

Vitamin B6 supplements are usually necessary when dietary intake of
vitamin B6 is lacking, or if a healthy diet is not being followed.
Often increasing dietary vitamin B6 is sufficient to restore body
stores of the vitamin, but supplements may be needed if this is not
possible.

Some people are more likely than others to have a vitamin B6
deficiency. Alcoholicsand the elderly often have a vitamin B6
deficiency because their diets may lack variety. In addition, alcohol
promotes the destruction and loss of vitamin B6 from the body.
Asthmatic children treated with the medicine theophylline may also
need supplementation with vitamin B6. Theophylline decreases body
stores of vitamin B6, and theophylline-induced seizures have been
linked to low body stores of the vitamin.

Too much vitamin B6

Too much vitamin B6 can result in nerve damage to the arms and legs.
This neuropathy is usually related to high intake of vitamin B6 from
supplements, and is reversible when supplementation is stopped.
According to the Institute of Medicine, "Several reports show sensory
neuropathy at doses lower than 500 mg per day." The upper tolerable
intake level (UL) for vitamin B6 is 100 mg per day for all adults. The
risk of adverse effects increases as intake increases above the UL.

Side Effects
------------

Excessive vitamin B6 supplement intake has been reported to cause
problems with the nerves supplying the arms and legs.

Risks
-----

Interactions

Many drugs interfere with the metabolism and excretion of vitamin B6.
Smoking, alcohol, and diuretics such as Lasix (furosemide) increase
vitamin B6 excretion in the urine. The asthma drug theophylline also
reduces the stores of vitamin B6 and can result in seizures.

Some drugs influence the activity of vitamin B6. Some of these drugs
include isoniazid, which is used to treat tuberculosis, and L-dopa
(also called levodopa), which is used to treat a variety of neurologic
problems such as Parkinson's disease.. The interaction with isoniazid
has lead to some controversy. Treatment with isoniazid may induce a
coma or seizures, which can be reversed by vitamin B6. However, a
group of children receiving isoniazid did not exhibit neurological or
neuropsychiatric problems regardless of whether or not they took a
vitamin B6 supplement. Accordingly, some physicians recommend taking a
supplement that provides 100% of the RDA for B6 when isoniazid is
prescribed, which is usually enough to prevent symptoms of vitamin B6
deficiency. Not all physicians agree; some argue supplementation with
vitamin B6 is not justified in these patients.

Research
--------

Vitamin B6, homocysteine, and heart disease

A deficiency of vitamin B6, folic acid, or vitamin B12 may increase
levels of the amino acid homocysteine. Elevated homocysteine may be a
risk factor for heart disease and stroke. The evidence suggests that
high levels of homocysteine may damage coronary arteries or make it
easier for the blood clotting cells, called platelets, to clump
together and form a clot. Currently however, no evidence exists
suggesting that vitamin B6 intake reduces homocysteine levels and the
risk of heart disease.

History
-------

How vitamin B6 was discovered

Paul György described vitamin B6 in 1934. He isolated the chemical
from the class of vitamins referred to as vitamin B2. He conducted
experiments in rats that showed that vitamin B6 deficiency caused a
specific type of dermatitis.3

References
----------

1. ↑ Hollyer T, Boon H, Georgousis A, Smith M, Einarson A. The use
  of CAM by women suffering from nausea and vomiting during
  pregnancy. BMC Complement Altern Med. 2002 May 17;2:5. Abstract

2. ↑ Autism Research Institute. Vitamin B6 (and magnesium) in the
  treatment of autism.

3. ↑ Birch TW and Gyorgy P. A study of the chemical nature of
  vitamin B6 and methods for its preparation in a concentrated
  state. Biochem J. 1936 February; 30(2): 304–315. Abstract

External Links
--------------

USDA: National Nutrient Database for Standard Reference

Institute of Medicine: Home Page

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