Vitamin B6: what it is, what it tells you and when it’s tested

Vitamin B6 helps a great many enzymes do their work: it helps you use protein, make red blood cells and keep your nerves working. Your body cannot make it, so it comes from food. The blood test measures its active form, pyridoxal phosphate.

When it’s tested

Doctors order it when they suspect a shortage: for example with heavy drinking, kidney disease or dialysis, bowel conditions that absorb poorly, or some medicines. They also order it for tingling or nerve pain with no clear cause, and when someone taking supplements may have too much.

It is not a routine test for people who feel well. With a varied diet a shortage is rare, and the value is affected by inflammation and other factors, so on its own it says little.

That is why Rosa does not test it. Instead it looks at vitamin B12, haemoglobin and MCV, which show the most common B vitamin shortages and anaemias.

What it tells you, and what it does not

It shows how much active vitamin B6 is in your blood right now. If it is low, your body may be short of it. If it is high, a supplement is usually behind it.

It is not perfect. Inflammation, low albumin and kidneys that filter less can lower it even when your stores are fine. That is why your doctor reads it together with your symptoms and other tests.

That is why it is read together with other tests:

• Vitamin B12: Another B vitamin your nerves need
• Homocysteine: It rises when B6, B12 or folate is short
• Haemoglobin: A marked shortage can cause anaemia
• Albumin: When it is low, measured B6 falls too

Normal vitamin B6 levels

The lab decides what is normal. Some lab reports give 8.7 to 27.2 ng/mL, the same for men and women.

Some labs use nmol/L: the numbers are about four times higher. The range printed next to your result is what counts.

Labs often ask you to fast. If you take supplements, say so before the blood draw: they can raise the value for days.

What your result means

Find the row for your result, in ng/mL. If your report uses another unit, compare your value with the range printed there.

• Below 8.7: Low. Your body may be short of it. It happens with alcohol, kidney or bowel disease and some medicines. Ongoing inflammation can lower the value even without a real shortage. Talk to your doctor: they look at your symptoms and the cause.
• 8.7 to 27.2: Normal. Your body has enough. Nothing to do.
• Above 27.2: High. It almost always comes from a supplement. Many products contain it, including magnesium and anti-tiredness products. Too much for a long time can damage your nerves. Check your labels and talk to your doctor, especially if you have tingling in your hands or feet.

If your vitamin B6 is high or low

• High vitamin B6: It almost always comes from a supplement. If it lasts, it can cause tingling and nerve damage.
• Low vitamin B6: Rare with a varied diet. It happens with heavy drinking, kidney or bowel disease and some medicines.

Who is at risk of a vitamin B6 shortage

With a varied diet it is rare. It is more common in these cases:

• Alcohol: Heavy drinking lowers the active vitamin B6 in your blood.
• Kidneys working less well: People with kidney disease or on dialysis often have less.
• A bowel that absorbs poorly: Coeliac disease and inflammatory bowel disease can lower it.
• Inflammation: Inflammation that lasts lowers it in your blood.
• Some medicines: For example isoniazid for tuberculosis, and some anti-epileptics. Do not stop them on your own: talk to your doctor.

Symptoms of too little and too much

A shortage can cause:

• Cracks at the corners of your mouth and a red tongue
• Irritated, scaly skin
• Tiredness, with anaemia
• Low mood or confusion

Too much, on the other hand, mainly causes tingling, numbness or burning in your hands and feet, and sometimes trouble walking. Either way, talk to your doctor.

Too much vitamin B6: the risk of supplements

Food alone does not give you too much. The risk comes from supplements, especially if you take more than one or use them for months.

Too much vitamin B6 damages the nerves in your hands and feet: it is its best known harmful effect. The higher the dose, the sooner the symptoms appear, but lower doses taken for a long time can cause them as well.

Vitamin B6 is in many products: multivitamins, magnesium supplements, products for tiredness or for your period. Check the labels and add up what you take. If you have tingling, talk to your doctor: usually the supplement is stopped and the symptoms improve, sometimes slowly.

Where it is found: what to eat

Many everyday foods contain it. For example:

• Fish, such as tuna and salmon
• Meat, especially chicken and turkey, and liver
• Chickpeas and other legumes
• Potatoes, bananas and nuts
• Whole grains

A varied diet is usually enough. Do not take vitamin B6 supplements without a reason: ask your doctor.

What can skew the result

A few things change the value without changing your stores.

• Recent supplements: They can raise the value for days. Say so before the blood draw.
• Inflammation: An infection or an inflammatory condition lowers it in your blood.
• Low albumin: Albumin carries vitamin B6. If it is low, the value falls too.
• A tube left in the light: Vitamin B6 breaks down in light. The lab protects the sample.

When to worry

Talk to your doctor if:

• You have tingling, numbness or burning in your hands and feet, especially if you take supplements.
• Your vitamin B6 is above the range on your report and you take one or more supplements.
• It is below the range and you drink heavily, or have kidney or bowel disease.
• You have cracks at the corners of your mouth, a red tongue and tiredness that does not go away.
• You have trouble walking or lose your balance: see your doctor soon. If it comes on suddenly, or with weakness on one side of your body, call 112 or go to the emergency department.

Frequently asked questions

What does vitamin B6 do? It helps many enzymes do their work. It helps you use protein, make red blood cells, keep your nerves and brain working and clear homocysteine.

What are normal vitamin B6 levels? Some lab reports give 8.7 to 27.2 ng/mL. Some labs use nmol/L, with numbers about four times higher. The range on your own report is what counts.

Is high vitamin B6 dangerous? A slightly high value while you take a supplement is usually not serious. But too much vitamin B6 for a long time can damage your nerves. If you have tingling in your hands or feet, talk to your doctor.

Which foods contain vitamin B6? Fish, poultry, liver, legumes such as chickpeas, potatoes, bananas, nuts and whole grains. A varied diet is usually enough.

Should I take a vitamin B6 supplement? Usually not. It makes sense only if your doctor finds a shortage or a specific reason. Taking it without need does not help and, over time, can do harm.

Does Rosa test vitamin B6? No. Rosa measures vitamin B12, haemoglobin and MCV, which show the most common vitamin shortages and anaemias. If your doctor wants vitamin B6, they order it separately.

Sources

• ASST Grande Ospedale Metropolitano Niguarda, laboratory test catalogue: vitamin B6, reference values. Catalogo esami Niguarda
• Ueland and colleagues, direct and functional biomarkers of vitamin B6 status. Annual Review of Nutrition, 2015. PMID 25974692
• EFSA Panel on Nutrition, Novel Foods and Food Allergens, scientific opinion on the tolerable upper intake level for vitamin B6. EFSA Journal, 2023. PMID 37207271
• Hadtstein and Vrolijk, vitamin B6 induced neuropathy: exploring the mechanisms of pyridoxine toxicity. Advances in Nutrition, 2021. PMID 33912895