Vitamin B6 — Food Sources, Benefits, Pregnancy, and Toxicity

Arpi Gasparyan | Обновлено: Май 27, 2024

Introduction

Vitamin B6 is a water-soluble vitamin of the B complex. It includes six compounds (vitamers): pyridoxine, pyridoxal, pyridoxamine, and their esters. Vitamin B6 is required for various biochemical reactions in the body and cellular metabolism regulation (1, 2).

Vitamin B6 is found in many foods, either synthesized naturally or added artificially, and available as a dietary supplement.

Содержание

Physiological Role & Absorption

Recommended Intakes

Vitamin B6 Food Sources

Dietary Supplements

Vitamin B6 & Health Benefits

Cardiovascular Disease

Cancer

Cognitive Function

Headaches

Eye Disorders

Premenstrual Syndrome (PMS)

Vitamin B6 and Pregnancy

Vitamin B6 Deficiency: Risk Groups and Symptoms

Vitamin B6 Toxicity & Tolerable Upper Limits

Vitamin B6 Contraindications & Interactions With Medications

Summary

References

Physiological Role & Absorption

Vitamin B6 has two active coenzyme forms: pyridoxal phosphate (PLP) and pyridoxamine phosphate (PMP).

They are required for over 140 enzymatic reactions in the body, such as amino acid, protein, carbohydrate, and lipid metabolism, and the first step of porphyrin synthesis.

Vitamin B6 is needed for brain development and cognition as it participates in the synthesis of neurotransmitters (such as serotonin and dopamine) and the maintenance of normal serum homocysteine levels. It is also involved in glucose metabolism (gluconeogenesis, or the formation of glucose from non-carbs, and glycogenolysis, or the breakdown of glycogen into glucose), immune function (lymphocyte and IL-2 production), and the formation of hemoglobin (red blood cells).

Vitamin B6 absorption occurs in the small intestines, primarily the jejunum. Phosphorylated forms are converted to their free forms and then absorbed by passive diffusion (1, 2, 3).

Recommended Intakes

According to the 2020-2025 Dietary Guidelines for Americans, the recommended dietary allowance (RDA) of vitamin B6 for adults is 1.3mg daily (4).

The table below shows the RDAs of vitamin B6 based on age, sex, pregnancy, and lactation.

	2-3 years	4-8 years	9-13 years	14-18 years	19-50 years	51+ years
Male	0.5mg	0.6mg	1.0mg	1.3mg	1.3mg	1.7mg
Female	0.5mg	0.6mg	1.0mg	1.2mg	1.3mg	1.5mg
Pregnancy	-	-	-	1.9mg	2.0mg	-
Lactation	-	-	-	1.9mg	2.0mg	-

Vitamin B6 Food Sources

Vitamin B6 is found in meat and plant-based products. It is found in the highest quantities in fish, meat (predominantly liver), and starchy vegetables such as potatoes and noncitrus fruits. B6 can also be artificially added to breakfast cereals.

The bioavailability of vitamin B6 from mixed diets is around 75%.

The table below shows foods rich in vitamin B6 and their levels per average serving size.

Food	Vitamin B6 per Serving Size
Skipjack tuna, cooked	0.83mg in 3 oz (85g)
Sockeye salmon, cooked	0.7mg in 3 oz
Turkey meat, cooked	0.52mg in 3 oz
Pork liver, cooked	0.48mg in 3 oz
Beef liver, cooked	0.87mg in 3 oz
Bananas	0.55 mg in 1 cup (150g)
Rye	0.49mg in 1 cup (169g)
White rice, long-grain, cooked	0.15mg in 1 cup (158g)
Durian	0.77mg in 1 cup (243g)
Sunflower seeds, dried	0.6mg in 1 cup (46g)
Jackfruit	0.49mg in 1 cup (151g)
Pistachio	0.48mg in 1 oz (28.35g or 49 kernels)
Spinach, cooked	0.43mg in 1 cup (180g)
Soybeans, mature, cooked	0.4mg in 1 cup (173)
Chickpeas, cooked	0.23mg in 1 cup (164g)

For more vitamin B6-rich foods, you can visit our “Foods high in vitamin B6” page; you can also visit this page for non-meat options.

Dietary pyridoxine in vegetables, fruits, and grains is glycosylated and has reduced bioavailability.

Dietary Supplements

Vitamin B6 is sold alone or in multivitamin forms with other B-complex vitamins. Supplemental vitamin B6 is commonly in the form of pyridoxine (pyridoxine hydrochloride) but can also be pyridoxal phosphate.

Supplements are available in oral capsules or tablets and liquids.

Vitamin B6 & Health Benefits

Cardiovascular Disease

There’s a hypothesis that vitamin B6, vitamin B12, and folate might reduce the risk of heart disease by lowering serum homocysteine concentrations. A trial with over 5,500 individuals with heart disease found that supplementation with these vitamins for 5 years reduced homocysteine levels and the risk of stroke by 25%; however, the study did not include people supplementing with only vitamin B6 (1).

A cross-sectional analysis of over 65,000 people found an inverse association between vitamin B6 intake and heart disease prevalence in adults aged ≥ 20 years (1, 5).

Nevertheless, several other large clinical trials failed to support the hypothesis. A clinical trial found no associations between multivitamin intake and cardiovascular disease risk. Two large controlled trials, including participants receiving only vitamin B6, also found no beneficial effects on major cardiovascular events in those with ischemic heart disease. Additionally, another trial found no link between multivitamin intake and stroke, cardiovascular events, or death risk in people who had suffered a stroke (1).

Cancer

Low vitamin B6 may be linked to certain types of cancers. According to a meta-analysis, people with increased vitamin B6 intake had a 20% lower colorectal cancer risk than those with the lowest intake. Another study suggested that high vitamin B6 intake may be protective against the development of pancreatic cancer; clinical trials are required to examine this relation. However, clinical trials to date have failed to find a link between vitamin B6 supplementation and cancer risks or its impact on mortality (1, 6, 7).

A study identifying 121 observational studies and 9 trials concluded that a higher intake of vitamin B6 levels from food only and high serum pyridoxal phosphate is associated with a lower risk of various cancer types, mainly gastrointestinal carcinomas. However, the controlled trials' findings did not support this vitamin's protective effect against cancer (8).

Cognitive Function

Vitamin B supplements containing B6, B12, and folate are hypothesized to delay cognitive decline in older adults due to lowered serum homocysteine levels. Sufficient dietary intake of these vitamins is associated with overall better cognitive performance in verbal fluency, attention, and memory (9, 10).

Data analysis found associations between higher vitamin B6 levels in the blood and better memory scores in 70 men aged 54 to 81. However, a review of 14 randomized controlled trials, mainly of low quality, demonstrated little evidence of an effect of vitamin B6 supplements alone or with vitamin B12 and folic acid on cognitive function in individuals with normal cognitive function, dementia, or ischemic vascular disease. A Cochrane Review failed to find evidence that 5-12 week supplementation improves cognitive function or mood (1).

Headaches

Vitamin B6 intake, alone or combined with vitamin B1, vitamin B12, and folate intake, is inversely associated with severe headaches and episodic migraines.

A study showed that combining the mentioned vitamins might effectively help treat episodic migraine and be a preventive measure (11, 12).

Daily intake of vitamin B6 and folate may synergistically interact with each other and possibly prevent migraine (11).

Eye Disorders

In an animal study, vitamin B6 has been shown to suppress pathological changes in the retina (retinal neovascularization), thus beneficially affecting eye diseases (13).

A cohort study of 963 older adults (73 years or older) suggested a strong association between normal folate levels in the blood, high dietary intake of vitamin B5 and B6, and a decreased risk for developing advanced age-related macular degeneration and vision loss (14).

Premenstrual Syndrome (PMS)

There’s evidence that vitamin B6 supplements might reduce PMS symptoms, but conclusions are limited as most studies have poor quality. A meta-analysis of nearly 1,000 women with PMS demonstrated that vitamin B6 supplementation is more effective than placebo in managing PMS symptoms.

In a randomized controlled trial, 94 women were given 80mg of pyridoxine daily for 3 menstrual cycles. They had statistically reduced PMS symptoms, such as depressed mood, anxiety, irritability, forgetfulness, and bloating. More research is required before final conclusions (1).

Vitamin B6 and Pregnancy

Morning sickness is quite common in the first months of pregnancy; 50-80% of individuals have nausea but no vomiting. The symptoms may persist throughout the day and affect social and physical functioning.

Two randomized trials noted that 30-75mg of oral vitamin B6 (pyridoxine) daily supplementation significantly decreased nausea in pregnant individuals. On the other hand, other studies on interventions for nausea and vomiting could not draw firm conclusions about the role of vitamin B6 in the management of morning sickness during pregnancy (1).

Randomized trials have shown that combining vitamin B6 with doxylamine might reduce the symptoms of morning sickness by 70% and decrease hospitalization rates.

The American College of Obstetrics and Gynecology (ACOG) recommends taking vitamin B6 3 to 4 times daily to treat nausea and vomiting in pregnancy (1, 15).

Vitamin B6 Deficiency: Risk Groups and Symptoms

Even though vitamin B6 deficiency is rare in the US, several groups of people are at risk of developing it. Vitamin B6 deficiency commonly occurs with other B-complex vitamin deficiencies, such as vitamin B12 and folate.

The reasons vary from dietary restrictions to medical conditions (1, 16):

Chronic kidney disease, including end-stage kidney disease and renal insufficiency. Poor kidney functioning is associated with low levels of PLP in the plasma due to its increased breakdown in those receiving hemodialysis or peritoneal dialysis and those who have undergone kidney transplantation.
Autoimmune disorders. For example, people with rheumatoid arthritis commonly have low levels of vitamin B6, and the deficiency worsens with disease severity. Gastrointestinal autoimmune disorders, such as celiac disease, Crohn’s disease, and ulcerative colitis, may also lead to decreased PLP plasma levels.
Bariatric and other gastrointestinal surgeries
Chronic alcohol dependence. Alcohol produces acetaldehyde, decreasing PLP formation in our cells and competing with PLP to bind proteins.
Genetic diseases, such as homocystinuria
Medications, such as several antibiotics and antiepileptics.

People with borderline vitamin B6 levels or mild deficiency may be asymptomatic for months or years. Vitamin B6 deficiency may lead to microcytic anemia, EEG changes, dermatitis, cheilosis (lip scaling and cracks at the corners of the mouth), tongue and mouth inflammation, depression, confusion, peripheral neuropathy, paresthesias, and weakened immune response.

Low levels of vitamin B6 in infants may cause irritability and seizures (1, 16).

Vitamin B6 Toxicity & Tolerable Upper Limits

Long-term intake of 1 to 6g of vitamin B6 daily may lead to severe and progressive sensory neuropathy characterized by ataxia (poor muscle control leading to uncontrolled movements). The severity of symptoms is dose-dependent, and the symptoms disappear when the person stops taking the supplements.

Other symptoms of vitamin B6 toxicity include painful skin lesions, sun allergy, nausea, vomiting, and heartburn (1).

There are established tolerable upper limits (ULs) for daily dietary and supplemental vitamin B6 intake. The ULs are the same between sexes and physiological processes such as pregnancy and lactation (1):

1-3 years	4-8 years	9-13 years	14-18 years	19+ years
30mg	40mg	60mg	80mg	100mg

The ULs do not apply to people prescribed vitamin B6 by a healthcare provider.

Vitamin B6 Contraindications & Interactions With Medications

Vitamin B6 supplementation is contraindicated for those with a history of allergic reactions to supplements containing the vitamin.

Vitamin B6 may interact with several medications (1, 16):

Antibiotics. Isoniazid and cycloserine (Seroycin) are antibiotics used to treat tuberculosis. Isoniazid may block the action of pyridoxine, reducing its levels in the blood, whereas cycloserine may increase its loss through urine. Pyridoxine supplements may be advised for those taking these medications.
Antiepileptic medications. Medications such as valproic acid (Depakene), carbamazepine (Carbatrol, Tegretol), and phenytoin (Dilantin) can increase the breakdown rate of vitamin B6 and lead to decreased vitamin B6 and increased homocysteine levels.
Penicillamine (Cuprimine)
Levodopa
Theophylline (Aquaphyllin, Elixophyllin). Theophylline is used to treat pulmonary diseases such as asthma and may lead to low plasma levels of PLP.

Summary

Vitamin B6 is a water-soluble vitamin of the B complex. It includes six compounds (vitamers), from which the active coenzyme forms of the vitamin are pyridoxal phosphate (PLP) and pyridoxamine phosphate (PMP).

Vitamin B6 is the richest in fish, meat (predominantly liver), and starchy vegetables such as potatoes and noncitrus fruits. B6 can also be artificially added to breakfast cereals.

Vitamin B6 is commonly reported with the deficiency of other B-complex vitamins. People with chronic kidney disease, autoimmune disorders, gastrointestinal surgeries, alcohol dependency, and anti-tuberculosis and anticonvulsant medications are at a greater risk of vitamin deficiency.

Vitamin B6 intake and its impact on health (cardiovascular disease, cancer, eye disorders, cognitive performance, and dementia) shows controversial results or poor-quality evidence. The results are comparably consistent for the beneficial effects of vitamin B6 intake and reduced symptoms of PMS, and nausea and vomiting during pregnancy.

References

Автор статьи: Arpi Gasparyan

Специальность: General Medicine at YSMU

Обновлено: Май 27, 2024

Проверено Victoria Mazmanyan