What are some current issues and controversies about vitamin B6?

Vitamin B6 and the nervous systemVitamin B6 is needed for the synthesis of neurotransmitters such as serotonin and dopamine []. 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 syndromeVitamin 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 syndromeVitamin 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 medicationsThere 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 Recommended Dietary Allowance for vitamin B6 for adults?

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].

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, ?c 2.00 100
Potato, Baked, flesh and skin, 1 medium 0.70 35
Banana, raw, 1 medium 0.68 34
Garbanzo beans, canned, ?c 0.57 30
Chicken breast, meat only, cooked, ?breast 0.52 25
Ready-to-eat cereal, 25% fortified, ?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, ?c 0.14 8
Tomato juice, canned, 6 oz 0.20 10
Avocado, raw, sliced, ?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, ?c 0.18 10
Peanut butter, smooth, 2 Tbs. 0.15 8
Walnuts, English/Persian, 1 oz 0.15 8
Soybeans, green, boiled, drained, ?c 0.05 2
Lima beans, frozen, cooked, drained, ?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 Vitamin B6 (pyridoxine)

Vitamin B6, also called pyridoxine, is one of eight water-soluble B vitamins. Vitamin B6 (pyridoxine) serves as coenzyme and is involved in the metabolism of protein and carbohydrates, the production of insulin and red and white blood cells, and the synthesis of neurotransmitters, enzymes, and prostaglandins. Vitamin B6 is essential in numerous biochemical pathways
involving red blood cells, the immune system, central nervous system function, protein metabolism, homocysteine metabolism, and also the production of energy. Pyridoxine is an especially important vitamin for maintaining healthy nerve and muscle cells and it aids in the production of DNA and RNA, the body's genetic material. It is necessary for proper absorption of vitamin B12 and for the production of red blood cells and cells of the immune system.

More specifically, Vitamin B6 consists of six specific compounds, namely pyridoxine, pyridoxal, pyridoxamine, and their respective phosphates, the latter group of which are the most active components in numerous reactions involving amino acid and protein metabolism. There are six forms of Vitamin B6: pyridoxal (PL), pyridoxine (PN), pyridoxamine (PM), and their phosphate derivatives: pyridoxal 5'-phosphate (PLimmune system. P), pyridoxine 5'-phosphate (PNP), and pridoxamine 5'-phospate (PNP). PLP is the active coenzyme form, and has the most importance in human metabolism. In the body, pyridoxine is found primarily in the liver and muscles. Pyridoxine is utilized by the liver to synthesize pyridoxal phosphate (PLP), the active coenzyme form. PLP functions as transamination and decarboxylation coenzymes, which are involved in amino acid and protein metabolism. PLP is also involved as a coenzyme in the synthesis of heme, niacin and serotonin. Alcohol impairs Vitamin B6 metabolism in the body.

The major forms of Vitamin B6 from animal products are pryridoxal 5'-phosphate and pyridoxamine 5'-phosphate. The major forms of Vitamin B6 from plant-derived foods are pyridoxine, pyridoxine 5'-phosphate and pyridoxine glucosides. Pyridoxine hydrochloride is the principal form of Vitamin B6 used for food fortification and in nutritional supplements. Pyridoxal 5'-phosphate is also available as a nutritional supplement. Pyridoxal 5'-phosphate, is involved in a wide range of biochemical reactions, including the metabolism of amino acids and glycogen, the synthesis of nucleic acids, hemogloblin, sphingomyelin and other sphingolipids, and the synthesis of the neurotransmitters serotonin, dopamine, norepinephrine and gamma-aminobutyric acid (GABA).