Vitamin B12 is a relatively non-toxic substance. Even high doses are unlikely to cause problems for most people. In fact, a maximum daily dosage has not been established for the vitamin, due to its non-toxic nature.
Signs of Vitamin B12 Toxicity
There are no signs of vitamin B12 toxicity, per se. There are a few rarely reported side effects that might be attributable to the vitamin, but such side effects are not necessarily related to the dose. These possible side effects include:
- Blood clots in the legs
- Feelings of swelling over the entire body
- Signs of an allergic reaction, such as:
- Hives or a rash
- Swelling of the lips, mouth, or throat
- Wheezing or other difficulty breathing.
What Causes Toxicity?
toxicity is due to an obvious cause -- taking too much. The Recommended Dietary Allowance for vitamin B12
for adults ranges from 2.4 to 2.8 mcg daily, depending on several factors (see Vitamin B12 Dosage)
. For nutrients that can cause toxicity, a "Tolerable Upper Intake Level" (UL) is given. This is the maximum that can be taken from all sources, including the diet, without causing significant toxicity. There are no UL values for vitamin B12
, since the risk of toxicity is quite low.