Vitamin B6: What is it?
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Vitamin B6 is a water-soluble vitamin that exists in three major chemical forms:
pyridoxine, pyridoxal, and pyridoxamine [1,
2]. It performs a wide variety of functions
in your body and is essential for your good health. For example, vitamin B6 is
needed for more than 100 enzymes involved in protein metabolism. It is also essential for
red blood cell metabolism. The nervous and immune systems need vitamin B6 to
function efficiently, [3-6] and it is also
needed for the conversion of tryptophan (an amino acid) to niacin (a vitamin)
[1,7].
Hemoglobin within red blood cells carries oxygen to tissues. Your body needs
vitamin B6 to make hemoglobin. Vitamin B6 also helps increase the
amount of oxygen carried by hemoglobin. A vitamin B6 deficiency can result in
a form of anemia [1] that is similar to iron
deficiency anemia.
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An immune response is a broad term that describes a variety of
biochemical changes that occur in an effort to fight off infections. Calories, protein,
vitamins, and minerals are important to your immune defenses because they promote the growth
of white blood cells that directly fight infections. Vitamin B6, through its
involvement in protein metabolism and cellular growth, is important to the immune system.
It helps maintain the health of lymphoid organs (thymus, spleen, and lymph nodes) that make
your white blood cells. Animal studies show that a vitamin B6 deficiency can
decrease your antibody production and suppress your immune response
[1,5].
Vitamin B6 also helps maintain your blood glucose (sugar) within a normal
range. When caloric intake is low your body needs vitamin B6 to help convert
stored carbohydrate or other nutrients to glucose to maintain normal blood sugar levels.
While a shortage of vitamin B6 will limit these functions, supplements of this
vitamin do not enhance them in well-nourished individuals
[1,8-10].
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What foods provide vitamin B6?
Vitamin B6 is found in a wide variety of foods including fortified cereals, beans, meat,
poultry, fish, and some fruits and vegetables [1,
11]. The table of selected food sources of
vitamin B6 suggests many dietary sources of B6.
Table of Food
Sources of Vitamin B6 [11]
| 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. |
What is the Recommended Dietary Allowance for vitamin B6 for adults?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 [12].
The 1998 RDAs for vitamin B6 [12] for adults, in milligrams, are: | 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) [12,
13] and the Continuing Survey of Food Intakes by
Individuals (1994-96 CSFII) [12], indicated that
diets of most Americans meet current intake recommendations for vitamin B6
[12]. |
When can a vitamin B6 deficiency occur?
Clinical signs of vitamin B6 deficiency are rarely seen in the United States. Many older
Americans, however, have low blood levels of vitamin B6, which may suggest a marginal or
sub-optimal vitamin B6 nutritional status. Vitamin B6 deficiency can occur in
individuals with poor quality diets that are deficient in many nutrients. Symptoms occur during later
stages of deficiency, when intake has been very low for an extended time. Signs of vitamin B6
deficiency include dermatitis (skin inflammation), glossitis (a sore tongue), depression, confusion,
and convulsions [1,
12]. Vitamin B6 deficiency also can cause
anemia [1,12,
14]. Some of these symptoms can also result from a
variety of medical conditions other than vitamin B6 deficiency. It is important to have
a physician evaluate these symptoms so that appropriate medical care can be given.
Who may
need extra vitamin B6 to prevent a deficiency?
Individuals with a poor quality diet or
an inadequate B6 intake for an extended period may benefit from taking a vitamin B6
supplement if they are unable to increase their dietary intake of vitamin B6
[1,15].
Alcoholics and older adults are more likely to have inadequate vitamin B6 intakes than other
segments of the population because they may have limited variety in their diet. Alcohol also promotes
the destruction and loss of vitamin B6 from the body.
Asthmatic children treated
with the medicine theophylline may need to take a vitamin B6 supplement
[16]. Theophylline decreases body stores of
vitamin B6 [17], and theophylline-induced
seizures have been linked to low body stores of the vitamin. A physician should be consulted about
the need for a vitamin B6 supplement when theophylline is prescribed.
What are some current issues and controversies about
vitamin B6?Vitamin B6 and the nervous system
Vitamin B6 is needed for the synthesis of neurotransmitters such as serotonin and
dopamine [1]. These neurotransmitters are required
for normal nerve cell communication. Researchers have been investigating the relationship between
vitamin B6 status and a wide variety of neurologic conditions such as seizures, chronic
pain, depression, headache, and Parkinson's disease [18].
Lower levels of serotonin have been found in individuals suffering from depression and
migraine headaches. So far, however, vitamin B6 supplements have not proved effective for
relieving these symptoms. One study found that a sugar pill was just as likely as vitamin B6
to relieve headaches and depression associated with low dose oral contraceptives
[19].
Alcohol abuse can result in neuropathy,
abnormal nerve sensations in the arms and legs [20].
A poor dietary intake contributes to this neuropathy and dietary supplements that include
vitamin B6 may prevent or decrease its incidence
[18].
Vitamin B6 and carpal tunnel syndrome
Vitamin B6 was
first recommended for carpal tunnel syndrome almost 30 years ago
[21]. Several popular books still recommend taking
100 to 200 milligrams (mg) of vitamin B6 daily to treat carpal tunnel syndrome, even
though scientific studies do not indicate it is effective. Anyone taking large doses of
vitamin B6 supplements for carpal tunnel syndrome needs to be aware that the
Institute of Medicine recently established an upper tolerable limit of 100 mg per day for adults
[12]. There are documented cases in the literature
of neuropathy caused by excessive vitamin B6 taken for treatment of carpal tunnel
syndrome [22].
Vitamin B6 and
premenstrual syndrome
Vitamin B6 has become a popular remedy for treating the
discomforts associated with premenstrual syndrome (PMS). Unfortunately, clinical trials have failed
to support any significant benefit [23]. One recent
study indicated that a sugar pill was as likely to relieve symptoms of PMS as vitamin B6
[24]. In addition, vitamin B6 toxicity has been seen in increasing numbers of women taking
vitamin B6 supplements for PMS. One review indicated that neuropathy was present in 23
of 58 women taking daily vitamin B6 supplements for PMS whose blood levels of B6
were above normal [25]. There is no convincing scientific
evidence to support recommending vitamin B6 supplements for PMS.
Vitamin B6 and interactions with medications
There are many drugs that
interfere with the metabolism of vitamin B6. Isoniazid, which is used to treat tuberculosis,
and L-DOPA, which is used to treat a variety of neurologic problems such as Parkinson's disease,
alter the activity of vitamin B6. There is disagreement about the need for routine
vitamin B6 supplementation when taking isoniazid
[26,27].
Acute isoniazid toxicity can result in coma and seizures that are reversed by vitamin B6,
but in a group of children receiving isoniazid, no cases of neurological or neuropsychiatric
problems were observed regardless of whether or not they took a vitamin B6 supplement.
Some doctors 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. It is important to consult with a physician about the need for a vitamin B6
supplement when taking isoniazid.
What is the relationship between vitamin B6, homocysteine, and heart disease?
A deficiency
of vitamin B6, folic acid, or vitamin B12 may increase your level of homocysteine, an
amino acid normally found in your blood [28]. There
is evidence that an elevated homocysteine level is an independent risk factor for heart disease and
stroke [29-37]. The evidence suggests that high levels
of homocysteine may damage coronary arteries or make it easier for blood clotting cells called platelets
to clump together and form a clot. However, there is currently no evidence available to suggest that
lowering homocysteine level with vitamins will reduce your risk of heart disease. Clinical intervention
trials are needed to determine whether supplementation with vitamin B6, folic acid, or
vitamin B12 can help protect you against developing coronary heart disease.
What is the health risk of 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, [28] 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" [12].
As previously mentioned, the Food and Nutrition Board of the Institute of Medicine has established
an upper tolerable intake level (UL) for vitamin B6 of 100 mg per day for all adults
[12]. "As intake increases above the UL, the risk
of adverse effects increases [12]."
Vitamin B6 intakes and healthful
dietsVitamin B6 is found in a wide variety of foods. Foods such as fortified
breakfast cereals, fish including salmon and tuna fish, meats such as pork and chicken, bananas,
beans and peanut butter, and many vegetables will contribute to your vitamin B6 intake.
According to the 2005 Dietery Guidelines for Americans, "Nutrient needs should be met
primarily through consuming foods. Foods provide an array of nutrients and other compounds that
may have beneficial effects on health. In certain cases, fortified foods and dietary supplements
may be useful sources of one or more nutrients that otherwise might be consumed in less than
recommended amounts. However, dietary supplements, while recommended in some cases, cannot
replace a healthful diet."
The Dietary Guidelines for Americans describes a healthy
diet as one that:
- emphasizes a variety of fruits, vegetables, whole grains, and fat-free
or low-fat milk and milk products;
- includes lean meats, poultry, fish, beans, eggs, and nuts;
- is low in saturated fats, trans fats, cholesterol, salt (sodium), and added sugars; and
- stays within your daily calorie needs.
For more information about building a healthful diet, refer to the
Dietary Guidelines for Americans
and the U.S. Department of Agriculture's food guidance system,
MyPyramid.
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