2 doctors weighed in:

Why would I have high B12 levels in my blood?

2 doctors weighed in
Dr. Scott Beede
Internal Medicine
1 doctor agrees

In brief: High intake

Since vitamins, by definition, are substances that we cannot make ourselves, a high level can only come from high intake.
Vitamin B12 is not very toxic, but in high amounts can cause diarrhea, edema and increase risk of clots. If you are taking a vitamin B12 supplement, or injections you may want to cut back (discuss with your doctor if you are taking under a doctor's supervision).

In brief: High intake

Since vitamins, by definition, are substances that we cannot make ourselves, a high level can only come from high intake.
Vitamin B12 is not very toxic, but in high amounts can cause diarrhea, edema and increase risk of clots. If you are taking a vitamin B12 supplement, or injections you may want to cut back (discuss with your doctor if you are taking under a doctor's supervision).
Dr. Scott Beede
Dr. Scott Beede
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