|
Vitamin B6
What foods provide vitamin B6?
What is the Recommended Dietary Allowance for vitamin B6 for adults?
When can a vitamin B6 deficiency occur?
Who may need extra vitamin B6 to prevent a deficiency?
What are some current issues and controversies about vitamin B6?
Vitamin B6 and the nervous system
Vitamin B6 and carpal tunnel syndromeVitamin B6 and premenstrual syndrome
Vitamin B6 and interaction with medicationsWhat is the relationship between vitamin B6, homocysteine, and heart disease?
What is the health risk of too much vitamin B6?
Selected food sources of vitamin B6
Vitamin
B6: What is it
?
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.
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).
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.
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 III1988-94) (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)."
Selected
Food Sources of vitamin B6
(11)
As the 2000 Dietary
Guidelines for Americans state, "Different foods contain different nutrients
and other healthful substances. No single food can supply all the nutrients
in the amounts you need" (38). As the following table indicates, vitamin 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. If you want more information about building a healthful diet, refer
to the Dietary
Guidelines for Americans and the Food
Guide Pyramid.
Food |
Milligrams
|
%DV*
|
Ready-to-eat cereal, 100% fortified, 3/4 c |
2.00
|
100
|
Potato, Baked, flesh and skin, 1 medium |
0.70
|
35
|
Banana, raw, 1 medium |
0.68
|
34
|
Garbanzo beans, canned, 1/2 c |
0.57
|
30
|
Chicken breast, meat only, cooked, 1/2 breast |
0.52
|
25
|
Ready-to-eat cereal, 25% fortified, 3/4 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, 1/2 c |
0.14
|
8
|
Tomato juice, canned, 6 oz |
0.20
|
10
|
Avocado, raw, sliced, 1/2 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, 1/4 c |
0.18
|
10
|
Peanut butter, smooth, 2 Tbs. |
0.15
|
8
|
Walnuts, English/Persian, 1 oz |
0.15
|
8
|
Soybeans, green, boiled, drained, 1/2 c |
0.05
|
2
|
Lima beans, frozen, cooked, drained, 1/2 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. |
This fact sheet was developed by the Clinical Nutrition Service, Warren Grant Magnuson Clinical Center, National Institutes of Health (NIH), Bethesda, MD, in conjunction with the Office of Dietary Supplements (ODS) in the Office of the Director of NIH. The mission of ODS is to strengthen knowledge and understanding of dietary supplements by evaluating scientific information, stimulating and supporting research, disseminating research results, and educating the public to foster an enhanced quality of life and health for the U.S. population. The Clinical Nutrition Service and the ODS would like to thank the expert scientific reviewers for their role in ensuring the scientific accuracy of the information discussed in this fact sheet.
Updated 12/9/02
Index
of dietary supplement fact sheets
|
|