Vitamin B6 is one of the best studied of all of the B vitamins. It has a variety of chemical forms that all being with the prefix “pyr” and include pyridoxine, pyridoxal, pyridoxamine, pyridoxine phosphate, pyridoxal phosphate, and pyridoxamine phosphate.
Vitamin B6 was first researched in the mid-1930's although at this point it was not given this name but was referred to as "antidermatitis factor.” This term refers to the finding that dermatitis (skin inflammation) increased when foods containing B6 were eliminated from the diet. To this day, topical B6 creams are used in the treatment of dermatitis, notably for symptoms related to seborrheic dermatitis.
In Depth
Vitamin B6 is one of the best studied of all of the B vitamins. It has a variety of chemical forms that all being with the prefix “pyr” and include pyridoxine, pyridoxal, pyridoxamine, pyridoxine phosphate, pyridoxal phosphate, and pyridoxamine phosphate.
Vitamin B6 was first researched in the mid-1930's although at this point it was not given this name but was referred to as "antidermatitis factor.” This term refers to the finding that dermatitis (skin inflammation) increased when foods containing B6 were eliminated from the diet. To this day, topical B6 creams are used in the treatment of dermatitis, notably for symptoms related to seborrheic dermatitis.
Function
Since vitamin B6 is involved in more than 100 enzymatic reactions, this nutrient has a multitude of far-reaching physiological functions.
Most, if not all, chemical categories of molecules depend upon vitamin B6 for their production. For example, amino acids require adequate supplies of B6 for their manufacture while the synthesis of nucleic acids (DNA components) also requires this nutrient. Because of its relationship to the manufacture of amino acids and nucleic acids, which themselves are such critical parts of new cell formation, vitamin B6 can be regarded as an essential factor in the production of virtually all new cells. Phospholipids (cell membrane components that allow for cellular messaging) and heme (the protein center of red blood cells) also require vitamin B6 for their synthesis.
The processing of carbohydrate (sugar and starch) in our body depends on availability of vitamin B6 with this nutrient being particularly important in facilitating the catabolism of glycogen stored in muscle cells and the liver. Since the conversion of carbohydrates into energy plays such an important role in certain types of athletic events, researchers continue to examine the role that vitamin B6 plays in carbohydrate processing during physical performance.
Vitamin B6 plays a wide variety of roles in supporting the integrity of the nervous system and neurological activity. One area in which B6 is involved is in the synthesis of messaging molecules called amines, molecules that the nervous system relies upon in order to transmit messages from one nerve to another (these molecules are classified as “neurotransmitters” for this reason). Amine-containing neurotransmitters are synthesized from amino acids with vitamin B6 being the key nutrient enabling this formation to occur. Serotonin, melatonin, epinephrine, norepinephrine and GABA are some amine-derived neurotransmitters that require B6 for their production.
Another of vitamin B6’s critical roles comes from its ability to remove sulfur groups from other molecules. Its participation in these sulfation reactions makes it an integral factor in varied physiological functions, such as hormone balance and liver detoxificaiton, that depend upon sulfur-containing molecules.
Vitamin B6 plays a similar role with methyl-containing compounds, molecules that have one carbon and three hydrogen atoms. The transfer of methyl groups is a key process in allowing many important chemical events to occur in the body. For example, genes can be switched on and off through methyl group transfer, making vitamin B6 an important factor in the processes of cellular signaling. Through its role in methyl group metabolism, vitamin B6 also plays a role in ensuring that levels of homocysteine are kept within healthy range (excess homocysteine levels are related to the development of cardiovascular disease and other health conditions).
Deficiency: Causes and Symptoms
Insufficient dietary intake and smoking can contribute to vitamin B6 deficiency. Additionally, a variety of medications can deplete the body of vitamin B6; these are listed in the Drug-Nutrient Interactions section.
Since vitamin B6 is integral to the process of new cell formation, it plays a key role in the healthy function of body tissue, such as skin, which regenerates quickly. As such, symptoms of deficiency often first manifest in skin conditions. Eczema, seborrheic dermatitis and other skin disorders have been associated with vitamin B6 deficiency.
Symptoms of vitamin B6 deficiency also manifest in impairments to the nervous system and the synthesis of red blood cells since this nutrient plays such a vital role in these processes. Many nerve-related symptoms can manifest with inadequate consumption of vitamin B6 with convulsions and seizures being possible adverse events associated with severe deficiency. Reflecting its importance in the formation of red blood cells, vitamin B6 deficiency can result in symptoms of anemia, fatigue and malaise. Hypochromic, microcytic (pernicious) anemia is the condition associated with anemia that is exclusively related to vitamin B6 deficiency.
Toxicity: Causes and Symptoms
While deficiency of vitamin B6 can manifest in nervous system imbalances, high levels of supplemental vitamin B6 can also cause these adverse effects. These imbalances do not seem to occur until supplementation levels exceed 2 grams per day. Largely based upon the concerns for imbalanced nervous system activity, in 1997, the Institute of Medicine at the National Academy of Sciences set a Tolerable Upper Intake Level (UL) for vitamin B6 of 100 milligrams for adults 19 years and older
Impact of Cooking, Storage and Processing
While vitamin B6 has historically been described as one of the most stable of the B vitamins, cooking and processing actually greatly reduce the vitamin B6 content of foods. Canning vegetables results in approximately 60-80% nutrient loss; canning fruit, approximately 38% loss; freezing fruit, approximately 15% loss; converting grains to grain products, between 50-95% loss; and converting fresh meat to meat products, between 50-75% loss.
The amount of vitamin B6 lost during the heating that takes place in home cooking processes is dependent upon the acidity of the food with the more acidic foods, in general, being poorer at retaining their vitamin B6 content. Freezing vitamin B6-rich foods in a home freezer can result in reductions of approximately one-third to one-half of the total content.
Drug-Nutrient Interactions
Medications that decrease the availability of vitamin B6 in the body include:
Vitamin B6 interacts with numerous other B-complex vitamins. The conversion of tryptophan to vitamin B3 (niacin) is dependent upon vitamin B6. Research focusing on Down’s syndrome has shown, for example, that some of the niacin deficiency problems resolve with the intake of vitamin B6. Imbalances of vitamin B1 metabolism result in imbalanced metabolism of vitamin B6 while deficiency of vitamin B6 can also reduce the body’s absorption of vitamin B12. Finally, both vitamins B2 and B3 are necessary for the conversion of vitamin B6 into various different chemical forms.
Health Conditions
Individuals who have the following health conditions should pay special attention to dietary intake of vitamin B6:
Excellent sources of vitamin B6 include bananas, bell peppers, cauliflower, collard greens, crimini mushrooms, garlic, kale, mustard greens, tuna and turnip greens. Very good food sources include broccoli, brussel sprouts, cabbage, celery, cod, halibut, potatoes, snapper, Swiss chard and watermelon.
Public Recommendations
In 2000, the Institute of Medicine at the National Academy of Sciences set the following Recommended Dietary Allowances for vitamin B6: