Vitamin B6

What is vitamin B6?

Vitamin B6 is a collective name for a few related substances, from which your body makes the active form: pyridoxal phosphate. That active form sits as a helper in more than a hundred enzymes. Most of those convert amino acids, the building blocks of protein, and so with B6 you make, among other things, serotonin, dopamine and GABA, the substances your brain cells use to talk to each other, and the haem in your haemoglobin. B6 also clears homocysteine, together with folate and B12. B6 is in plenty of ordinary food: meat, fish, chicken, potatoes, bananas, legumes, nuts and whole grains. Anyone who eats a varied diet rarely runs short. That makes B6 different from B1 and B12: the ordinary problem here is not too little, but too much. B6 is the one B vitamin where a long-term high dose from supplements causes damage, to the sensory nerves in feet and hands. That is why the amount of B6 a supplement may contain in the Netherlands is capped. Your report shows vitamin B6 in nmol/L, measured as the active form in whole blood. Normal is about 50 to 110 nmol/L where the labs overlap, and it is precisely at the upper end that the labs differ considerably.

Why is vitamin B6 relevant?

B6 is a value you want to know mainly for one reason: you take a supplement and you have tingling. A B complex, a multivitamin, a magnesium tablet with B6 in it or a sports supplement together easily deliver many times what you need. Months of such a dose damage the long sensory nerves, and that starts with tingling, a numb or burning feeling in feet and hands and an unsteady feeling when walking. The damage is usually reversible once you stop, but recovery takes months. A B6 value shows whether the supplement can be the cause, and that is one of the few kinds of tingling with a simple solution. The other reason is less everyday: a low B6 in anyone who drinks a lot, has a long-standing inflammation, coeliac disease or another gut disease, or takes certain medicines. Alcohol breaks down the active form, and an inflammation pulls B6 out of the blood into the tissues. A deficiency gives vague symptoms, tiredness, a sore tongue, cracks at the corners of the mouth and low mood, and lets homocysteine rise. And B6 belongs to the story of homocysteine. Folate and B12 clear most of it, but the last step runs on B6. A high homocysteine with a normal folate and B12 is a reason to look at B6.

Vitamin B6 reference ranges

The band above is where the labs overlap, and for vitamin B6 the difference sits mainly at the upper end: the upper limit runs almost a factor of two apart between labs. That matters, because for B6 the upper end is genuinely read. So compare your value with the range on your own report, and weigh in what you take. There is no national normal value for B6.

Vitamin B6 high or low: what it means

A high B6 is almost always a supplement, and the question is not whether the value is high but whether you have symptoms. A high value without tingling is a reason to bring the dose down; a high value with tingling, numbness or an unsteady feeling when walking is a reason to stop. Count on months before the nerves recover. Without a supplement a high B6 is rare and usually a matter of the measurement: the vitamin is not stable for long after the draw, and the tube has to be processed quickly. A low B6 means too little supply, too much breakdown or a shift into the tissues. The most common explanation first: one-sided eating, alcohol, an inflammation or chronic disease, and medicines, including the pill, some drugs against tuberculosis and epilepsy, and long-term use of drugs for rheumatism. A low B6 often goes together with a low B1 or folate, because the sources in your diet overlap. What you do about it: if you take more than an ordinary multivitamin, add up how much B6 you take in altogether, because it is in more products than you think. With a deficiency, meat, fish, potatoes, bananas, legumes and less alcohol usually suffice; a supplement in an ordinary dose is fine then, long-term high is not. Read B6 beside B1, which comes from the same tube, beside homocysteine, and with a low value beside CRP, because an inflammation pushes B6 down without there being a deficiency. Always mention what you take: that changes the meaning of the value.

How does a vitamin B6 blood test work?

Referral

Not needed. You can have vitamin B6 measured yourself, and the value usually comes back together with vitamin B1.

Fasting

Not needed. If you want to measure your own store, skip the supplement on the day of the draw; if you want to know how high you sit with the supplement, take it as always.

The draw

One tube of whole blood from a vein in your arm, which has to reach the lab quickly and protected from light, because the vitamin is not stable for long after the draw.

The result

A single number in nmol/L, with an upper limit that differs considerably per lab; compare with the range on your own report.

Repeating

After stopping or lowering a supplement, after three months, and with tingling together with a check of the symptoms, because those recover more slowly than the value.

Where to draw

You can draw at 250+ locations near you, no referral needed. See the locations

Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.