Vitamin B6 - pyridoxine
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Vitamin B6 is a group of six related compounds, called “vitamers”. These include pyridoxine (what we sometimes think of as THE B6), pyridoxal, pyridoxamine, and their active forms: pyridoxal 5’-phosphate (abbreviated as P5P or PLP) pyridoxine 5’-phosphate, and pyridoxamine 5’phosphate. However, while pyridoxine may get the most credit, P5P is the more “active” B6, because it is the most biologically active form of all the vitamers and is involved in over 140 different enzymatic reactions in the body.
What does B6 do? As with all the B vitamins, it’s involved in energy metabolism and plays a role in amino acid, carbohydrate, and lipid metabolism. It’s biggest role, though, is in amino acid metabolism. As thiamin is to fats and riboflavin is to carbohydrates, so pyridoxine is to proteins. Pyridoxine also plays a big part in converting amino acids to neurotransmitters, transforming amino acids into glucose, and breaking down ammonia (a protein waste product). It’s not just about protein, though. B6 helps release glucose from the liver and from muscles during periods of exercise and fasting. It can help break down histamine and oxalates, build hemoglobin, and supports methylation. It’s a busy little molecule (remember—it’s in over 140 different enzymatic reactions!).
What happens if you don’t get enough B6? Several problems can start to pop up. Deficiency can cause neurologic symptoms—especially numbness and tingling in the hands and feet (peripheral neuropathy). Because of its role in making hemoglobin, deficiency can lead to anemia (specifically, “microcytic” anemia, where the red blood cells are small). It can lead to impaired immune function (meaning you may get sick more often), can increase risk of cardiovascular disease, and can affect thinking and behavior (which may show up as depression, anxiety, irritability, or difficulty sleeping).
Different forms of B6 are found in different types of food. Pyridoxine is the plant-based version of B6; pyridoxal is the animal-based version. The animal-based version is the type of B6 that is easiest for us to use (we are animals, after all); the plant-based version can be converted to the animal version through a series of steps (which requires energy, magnesium, and riboflavin). It’s worth noting that B6 in plants is also not always fully bioavailable, meaning that the amount you see listed on the nutritional content may not be the amount that you absorb—it is often bound to sugars in the form pyridixone-5’-beta-D-glucoside, which makes it harder to break down (in general, vitamins tend to be more bioavailable from animal sources than from plant sources). As a result, vegetarians and vegans may be at higher risk of B6 deficiency than omnivores.
Certain conditions can put you at higher risk for B6 deficiency. For example, people who are taking carbidopa/levodopa for Parkinson’s Disease can have lower B6 levels because carbidopa interacts with B6 metabolism. Riboflavin deficiency can make it harder to convert B6 into its active forms. Having high amounts of inflammation (rheumatoid arthritis, cardiovascular disease, etc) can increase needs for B6, as can a high protein diet (since B6 plays such an important role in protein metabolism). If your gut is not functionally optimally (from leaky gut or dysbiosis) you may not be able to absorb B6 efficiently. Rare genetic disorders can affect B6 metabolism—in these cases, patients may need high doses of pyridoxine, or may need P5P supplementation. Sulfites from foods (wine, dried fruits, cured meats, etc) can break down B6. Smoking and oral contraceptives may also increase needs for B6. As a result, while severe deficiency is relatively rare, marginal deficiencies are actually quite common—in the US, it may be upwards of 30%.
How much B6 do you need? The recommended daily allowance for B6 for most adults is 1.3 mg/dL, though it is higher for older adults and in pregnancy (in which case it goes up closer to 2 mg/dL). As with (most) other B vitamins, unfortified nutritional yeast is an excellent source – about half a tablespoon (depending on the source) gets you to the RDA. Liver, similarly, is an excellent source. Other sources include a variety of meats and fish, eggs, nuts, seeds, and whole grains (though in these last three B6 is typically in the pyridoxine form, which is less bioavailable), and some vegetables (especially cabbage and spinach). In addition to dietary sources, B6 can be supplemented. The two typical supplemental forms are pyridoxine (again, this is the plant form, which is less bioavailable) and pyridoxal 5’-phosphate (P5P), which is the most readily bioavailable form (and the preferred supplemental form as a result).
It’s worth noting, though, that as with niacin (B3), you CAN overdo it with B6. Signs of toxicity can be like signs of deficiency. Numbness and tingling is the big one, and the threshold for it to happen varies a lot from person to person (for some, it can happen at fairly low doses). The European Food Safety Association set an upper tolerable limit of 12 mg/dL. The Institute of Medicine, however, set an upper limit of 100 mg/dL. Toxicity is probably much more common with pyridoxine compared to P5P. The reason for this may be that high doses of pyridoxine inhibit the action of the active form—so even if levels of pyridoxine in the blood are high, it may not actually be functioning (interestingly, and perhaps unsurprisingly, the effect has not been seen with P5P). This is another reason to favor P5P over pyridoxine—and a reason to not overdo it with B6 supplementation. If you do supplement, I would start with a low dose (10 mg, though it’s probably ok to be more liberal with P5P) and gradually increase it over time, likely not exceeding 100 mg.
The best way to know your B6 status is to check it. This can be done with comprehensive micronutrient testing (such as the Nutreval). Plasma levels of B6 can be checked through a regular lab (Labcorp or Quest), though this test is not as robust as more specialized versions.
In summary, B6 represents a group of several compounds that play an important role in energy metabolism (especially protein metabolism). The most active form of which is pyridoxal 5’-phosphate (P5P), which is the form found in animal products. B6 insufficiency is relatively common, with some symptoms including poor sleep, poor mood, numbness and tingling, and anemia. Certain conditions (inflammation, certain drugs, etc) can increase needs for B6. Checking your status is a good way to know where you stand.
What’s your B6 status?
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