High vitamin B12: causes and when to worry

A high vitamin B12 usually comes from a supplement, a multivitamin or injections. On its own it causes no symptoms. If you take no B12 in any form, your doctor looks for the cause, usually starting with the liver and the blood.

What high vitamin B12 means

Your body uses the B12 it needs and keeps a store in the liver. When a lot comes in, from supplements or injections, the number in your blood rises.

If you take B12, it is usually not a problem. But if you take none in any form, a high number that stays high should not be ignored: it deserves a check with your doctor.

What causes high vitamin B12

The first two are the most common.

Symptoms

Usually none. A high B12 on its own causes no problems, and it is often found by chance.

If you feel tired or have tingling or other symptoms, talk to your doctor: they need looking into even when B12 is high.

High vitamin B12 without supplements

First check carefully what you take. B12 is in many multivitamins, in energy supplements, often in hair and nail supplements, and in some fortified drinks and cereals.

If you really take none, show the report to your doctor. They usually start with the liver tests and the blood count, and decide whether to repeat the test.

Which tests to read alongside it

These tests help show where it comes from.

What your result means

The upper end of the scale, in pg/mL.

How to lower high vitamin B12

It depends on the cause. Where to start:

When to worry

Talk to your doctor if:

Frequently asked questions

Is high vitamin B12 dangerous? Usually not in itself: it often reflects a supplement. But without supplements, a high number that stays high deserves a check with your doctor.

Can high vitamin B12 be a sign of cancer? If you take supplements, usually not: they are the most likely cause. Without supplements, a high number is found more often in people with liver, kidney or blood disorders, and sometimes cancer. That is why it should be seen by your doctor.

High vitamin B12 and the liver: what is the link? The liver is where B12 is stored. When it is unwell, for example with hepatitis or cirrhosis, it can release B12 into the blood. That is why, without supplements, the liver tests are checked.

When should you not take vitamin B12? When you do not need it: if your number is already high, more B12 does not help. If a deficiency is suspected, the test usually comes first, because a supplement can raise the number and hide the deficiency. Ask your doctor before starting, and if your doctor prescribed it, do not stop it on your own.

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