Vitamin B6

Synonym: pyridoxine

Characteristics: Vitamin B6 is a water-soluble vitamin that can be found naturally in many foods in 6 different forms. Vitamin B6 performs a wide range of functions in the body and is extremely versatile. More than 100 enzyme reactions are involved, mostly related to protein metabolism, but also carbohydrate and lipid metabolism. Vitamin B6 also plays a role in cognitive development through the biosynthesis of neurotransmitters, participates in immune functions and hemoglobin formation.

Absorption: The bioavailability of vitamin B6 is on average between 60‒90%. Prolonged heating, food storage, milling and grain processing cause significant losses of B6. Foods of plant origin lose very little vitamin B6 when cooked because they contain the most stable pyridoxine. While foods of animal origin, which mainly contain pyridoxal and pyridoxamine, lose a significant amount (on average 40‒70%). The absorbability of vitamin B6 from dietary supplements is similar to that from food sources and does not vary significantly between different forms of supplements. Although the body absorbs large pharmacological doses of vitamin B6 well, it quickly excretes most of the vitamin in the urine.

Dietary supplements: Vitamin B6 is available in multivitamins, in supplements containing other B complex vitamins, and as a separate dietary supplement. The most common vitamin B6 in dietary supplements is pyridoxine (in the form of pyridoxine hydrochloride).

Natural sources: Vitamin B6 is found in a wide variety of foods. The richest sources of vitamin B6 include fish, beef liver and other offal, chicken, pork, legumes, eggs, nuts, potatoes and other starchy vegetables, and fruits (except citrus). About 75% of vitamin B6 from a mixed diet is bioavailable.

Effect: Clinical research supports the use of vitamin B6 to relieve symptoms of PMS (especially breast tenderness and mood disorders), nausea in pregnancy, and as a treatment for hyperhomocysteinemia (usually with folate and B12).

Deficiency: Vitamin B6 deficiency is uncommon and is associated with anemia, dermatitis with cheilosis (scaly lips and cracks in the corners of the mouth), glossitis (swelling of the tongue), seborrheic dermatitis, depression and confusion, neuropathy, weakness, and weakened immune function. In infants, vitamin B6 deficiency causes irritability and convulsions. Kidney disease, celiac disease, Crohn's disease, ulcerative colitis, autoimmune diseases, and alcoholism can cause vitamin B6 deficiency. Taking certain medications, such as anti-epileptic drugs, can lead to B6 deficiency over time.

Recommended daily dose: adult 19‒50 years: 1.3 mg for men, 1.3 mg for women (1.9 mg during pregnancy, 2 mg when breastfeeding), adult 51+: 1.7 mg for men, 1.7 mg for women.

Side effects: Headache, drowsiness.

Interactions: Pyridoxine may increase the risk of drug-induced photosensitivity. Caution should be exercised in patients taking pyridoxine and amiodarone (an antiarrhythmic) at the same time. Antiepileptic drugs increase the catabolism of vitamin B6 and thereby reduce its concentration. Isoniazid (tuberculosis therapy), theophylline (COPD and asthma treatment) and oral contraceptives also increase vitamin B6 requirements. It is recommended to increase the intake of foods rich in vitamin B6 or consider a dietary supplement.

Pregnancy: Pyridoxine is commonly used during pregnancy to reduce symptoms of morning sickness.

Lactation: Very high doses of pyridoxine inhibit lactation; doses closer to physiological levels had no effect on lactation.

Toxicity: High intake of vitamin B6 from food did not cause adverse effects. However, chronic administration of 1–6 g of oral pyridoxine per day for 12–40 months can cause severe and progressive sensory neuropathy characterized by ataxia (loss of control over body movements). Symptoms usually stop when the patient stops taking pyridoxine supplements. Other effects of excessive vitamin B6 intake include painful, disfiguring dermatological lesions, photosensitivity, and gastrointestinal symptoms such as nausea and heartburn. The highest tolerable intake is 100 mg/day for an adult.