Vitamin B6 is a water-soluble vitamin that is naturally present in many foods, added to others, and available as a dietary supplement. It is the b vitamins and cv disease name for six compounds vitamers with vitamin B6 activity: Substantial proportions of the naturally occurring pyridoxine in fruits, vegetables, and grains exist in glycosylated forms that exhibit reduced bioavailability [ 3 ], b vitamins and cv disease.
Vitamin B6 in coenzyme forms performs a wide variety of functions in the body and is extremely versatile, with involvement in more than enzyme reactions, mostly concerned with protein metabolism [ 1 ].
Vitamin B6 also plays a role in cognitive development through the biosynthesis of neurotransmitters and in maintaining normal levels of homocysteine, an amino acid in the blood [ 3 ]. Vitamin B6 is involved in gluconeogenesis and glycogenolysis, immune function for example, it promotes lymphocyte and interleukin-2 productionand hemoglobin formation [ 3 ]. The human body absorbs vitamin B6 in the jejunum.
Phosphorylated forms of the vitamin are dephosphorylated, and the pool of free vitamin B6 is absorbed by passive diffusion [ 2 ]. Vitamin B6 concentrations can be measured directly by assessing concentrations of PLP; other vitamers; or total vitamin B6 in plasma, erythrocytes, or b vitamins and cv disease [ 1 ].
Vitamin B6 concentrations can also be calcium and diabetes indirectly by assessing either erythrocyte aminotransferase saturation by PLP or tryptophan metabolites. Plasma PLP is the most common measure of vitamin B6 status. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people.
These values, which vary by age and gender, include:. Table 1 lists the current RDAs for vitamin B6 [ 1 ], b vitamins and cv disease.
For infants from birth to 12 months, the FNB established an AI for vitamin B6 that is equivalent to the mean intake of vitamin B6 in healthy, breastfed infants. Vitamin B6 is found in a wide variety of foods [ 134 ]. The richest sources of vitamin B6 include fish, beef liver and other organ meats, potatoes and other starchy b vitamins and cv disease, and fruit other than citrus. In the United States, adults obtain most of their dietary vitamin B6 from fortified cereals, beef, poultry, starchy vegetables, and some non-citrus fruits [ 13b vitamins and cv disease ].
Food and Drug Administration FDA developed DVs to help consumers compare the nutrient contents of products within the context of a total diet. The DV for vitamin B6 used for the values in Table 2 is 2 mg for adults and children age 4 years and older [ 6 ]. This DV, however, is changing to 1. The updated labels must appear on food products and dietary supplements beginning in Januarybut they can be used now [ 8 ].
FDA does not require food labels to list vitamin B6 content unless a food has been fortified with this nutrient. Vitamin B6 is available in multivitamins, b vitamins and cv disease, in supplements containing other B complex vitamins, and as a stand-alone supplement [ 9 ].
The most common vitamin B6 vitamer in supplements is pyridoxine in the form of pyridoxine hydrochloride [HCl]although some supplements contain PLP. Vitamin B6 supplements b vitamins and cv disease available in oral capsules or tablets including sublingual and chewable tablets and liquids. Absorption of vitamin B6 from supplements is similar to that from food sources and does not differ substantially among the various forms of supplements [ 1 ]. Although the body absorbs large pharmacological doses of vitamin B6 well, it quickly eliminates most of the vitamin in the urine [ 10 ].
Adults aged 51 years or older and children younger than 9 are more likely than members of other age groups to take supplements containing vitamin B6. The average vitamin B6 intake is about 1. Among supplement users and nonusers, plasma PLP levels were much lower in women than men, non-Hispanic blacks than non-Hispanic whites, current smokers than never smokers, and people who were underweight than those of normal weight.
Teenagers had the lowest vitamin B6 concentrations, followed by adults aged 21—44 years. However, plasma PLP levels in the elderly were not particularly low, b vitamins and cv disease, even in those who did not use supplements.
Based on these data, the authors of this analysis concluded that the current RDAs might not guarantee adequate vitamin B6 status in many population groups [ 12 ]. PLP concentrations tend to be low in people with alcohol dependence; those who are obese; and pregnant women, especially those with preeclampsia or eclampsia [ 1 ]. Isolated vitamin B6 deficiency is uncommon; inadequate vitamin B6 status is usually associated with low concentrations of other B-complex vitamins, such as vitamin B12 and folic acid [ 2 ], b vitamins and cv disease.
Vitamin B6 deficiency causes biochemical changes that become more obvious as the deficiency progresses [ 2 ]. Vitamin B6 deficiency is associated with microcytic anemia, electroencephalographic abnormalities, dermatitis with cheilosis scaling on the lips and cracks at the corners of the mouth and glossitis swollen tonguedepression and confusion, and weakened immune function [ 12 ]. Individuals with borderline vitamin B6 concentrations or mild deficiency might have no deficiency signs or symptoms for months or even years.
In infants, vitamin B6 deficiency causes irritability, abnormally acute hearing, and convulsive seizures [ 2 ]. End-stage renal diseases, b vitamins and cv disease, chronic renal insufficiency, and other kidney diseases can cause vitamin B6 deficiency [ 3 ]. Certain genetic diseases, such as homocystinuria, can also cause vitamin B6 deficiency [ 2 ]. Some medications, such as antiepileptic drugs, can lead to deficiency over time. Frank vitamin B6 deficiencies are relatively rare in the United States but some individuals might have marginal vitamin B6 status [ 2 ].
The following groups are among those most likely to have inadequate intakes of vitamin B6. People with poor renal function, including those with end-stage renal disease and chronic renal insufficiency, often have low vitamin B6 concentrations [ 3 ]. Plasma PLP concentrations are also low in patients receiving maintenance kidney dialysis or intermittent peritoneal dialysis, as well as those who have undergone a kidney transplant, perhaps due to increased metabolic clearance of PLP [ 13 ].
Patients with kidney disease often show clinical symptoms similar b vitamins and cv disease those of people with vitamin B6 deficiency [ 13 ]. People with rheumatoid arthritis often have low vitamin B6 concentrations, and vitamin B6 concentrations tend to decrease with increased disease severity [ 3 ]. These low vitamin B6 levels are due to the inflammation caused by the disease and, in turn, increase the inflammation associated with the disease. Although vitamin B6 supplements can normalize vitamin B6 concentrations in patients with rheumatoid arthritis, they do not suppress the production of inflammatory cytokines or decrease levels of inflammatory markers [ 3b vitamins and cv disease, 14 ].
The mechanisms for this effect are not known. However, b vitamins and cv disease, celiac disease is associated with lower pyridoxine absorption, b vitamins and cv disease, and low PLP concentrations in inflammatory bowel disease could be due to the inflammatory response [ 3 ]. Plasma PLP concentrations tend to be very low in people with alcohol dependence [ 1 ].
Alcohol produces acetaldehyde, which decreases net PLP formation by cells and competes with PLP in protein binding [ 13 ]. As a result, the PLP in cells might be more susceptible to hydrolysis by membrane-bound phosphatase. People with alcohol dependence might benefit from pyridoxine supplementation [ 3 ]. Scientists have hypothesized that certain B vitamins folic acid, vitamin B12, and vitamin B6 might reduce cardiovascular disease risk by lowering homocysteine levels [ 115 ]. Therefore, several clinical trials have assessed the safety and efficacy of supplemental doses of B vitamins to reduce heart disease risk.
Evaluating the impact of vitamin B6 from many of these trials is challenging because these studies also included folic acid and vitamin B12 supplementation. Moreover, most other large clinical trials have failed to demonstrate that supplemental B vitamins actually reduce the risk of cardiovascular events, even though they lower homocysteine levels. The combined analysis of data from these two trials showed no benefit of vitamin B6 supplementation, with or without folic acid 0.
In a trial of adults who had suffered a nondisabling stroke, supplementation with high or low doses of a combination of vitamins B6 and B12 and folic acid for 2 years had no effect on subsequent stroke incidence, cardiovascular events, or risk of death [ 18 ].
The research to date provides little evidence that supplemental amounts of vitamin B6, alone or with folic acid and vitamin B12, can help reduce the risk or severity of cardiovascular disease and stroke. Some research has associated low plasma vitamin B6 concentrations with an increased risk of certain kinds of cancer [ 3 ]. However, the small number of clinical trials completed to date has not shown that vitamin B6 supplementation can help prevent cancer or reduce its impact on mortality.
For example, an analysis of data from two large randomized, double-blind, placebo-controlled trials in Norway found no association between vitamin B6 supplementation and cancer incidence, mortality, or all-cause mortality [ 20 ].
Poor vitamin B6 status has been hypothesized to play a role in the cognitive decline that some older adults experience [ 21 ]. Several studies have demonstrated an association between vitamin B6 and brain function in the elderly. For example, an analysis of data from the Boston Normative Aging Study found associations between higher serum vitamin B6 concentrations and better memory test scores in 70 men aged 54—81 years [ 22 ].
According to this review, most of the studies were of low quality and limited applicability. A Cochrane review found no evidence that short-term vitamin B6 supplementation for 5—12 weeks improves cognitive function or mood in the two studies that the authors evaluated [ 23 ]. The review did find some evidence that daily vitamin B6 supplements 20 mg can affect biochemical indices of vitamin B6 status in healthy older men, but these changes had no overall impact on cognition.
More evidence is needed to determine whether vitamin B6 supplements might help prevent or treat b vitamins and cv disease decline in elderly people. Some evidence suggests that vitamin B6 supplements could reduce the symptoms of premenstrual syndrome PMSbut conclusions are limited due to the poor quality of most studies [ 24 b vitamins and cv disease. A meta-analysis of nine published trials involving almost 1, women with PMS found that vitamin B6 is more effective in reducing PMS symptoms than placebo, but most of the studies analyzed were small and several had methodological weaknesses [ 24 ].
A more recent double-blind, randomized controlled trial in 94 women found that 80 mg pyridoxine taken daily over the course of three cycles was associated with statistically significant reductions in a broad range of PMS symptoms, including moodiness, irritability, b vitamins and cv disease, forgetfulness, bloating, and, especially, anxiety [ 25 ], b vitamins and cv disease.
The potential effectiveness of vitamin B6 in alleviating the mood-related symptoms of PMS could be due to its role as a cofactor in neurotransmitter biosynthesis [ 26 ]. Although vitamin B6 shows promise for alleviating PMS symptoms, more research is needed before drawing firm conclusions. Although this condition is generally known as "morning sickness," it often lasts throughout the day.
Prospective studies on vitamin B6 supplements to treat morning sickness have had mixed results. In two randomized, placebo-controlled trials, 30—75 mg of oral pyridoxine per day significantly decreased nausea in pregnant women who were experiencing nausea [ 2930 ]. The authors of a recent Cochrane review of studies on interventions for nausea and vomiting in pregnancy could not draw firm conclusions on the value of vitamin B6 to control the symptoms of morning sickness [ 28 ].
The American Congress of Obstetrics and Gynecology ACOG recommends monotherapy with 10—25 mg of vitamin B6 three or four times a day to treat nausea and vomiting in pregnancy [ 31 ]. Before taking a vitamin B6 supplement, pregnant women should consult a physician because doses could approach the UL. High intakes of vitamin B6 from food sources have not been reported to cause adverse effects [ 1 ].
However, chronic administration of 1—6 g oral pyridoxine per day for 12—40 months can cause severe and progressive sensory neuropathy characterized by ataxia loss of control of bodily movements [ 10]. Symptom severity appears b vitamins and cv disease be dose dependent, and the symptoms usually stop if the patient discontinues the pyridoxine supplements as soon as the neurologic symptoms appear. Other effects of excessive vitamin B6 intakes include painful, disfiguring dermatological lesions; photosensitivity; and gastrointestinal symptoms, such as nausea and heartburn [ 1232 ].
The scientific literature includes isolated case reports of congenital defects in the infants of women who took pyridoxine supplements during the first half of pregnancy [ 7 ]. However, a more recent observational study found no association between pyridoxine supplementation mean dose ULs are lower for children bleeding and blood pressure pills adolescents based on body size.
The ULs do not apply to individuals receiving vitamin B6 for medical treatment, but such individuals should be under the care of a physician. Vitamin B6 can interact with certain medications, and several types of medications might adversely affect vitamin B6 levels, b vitamins and cv disease. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin B6 status with their healthcare providers. In combination with pyridoxal phosphate, cycloserine increases urinary excretion of pyridoxine [ 9 ].
The urinary loss of pyridoxine might exacerbate the seizures and neurotoxicity associated with cycloserine. Pyridoxine supplements can help prevent these adverse effects.