Since B-12 is a water-soluble vitamin, your body usually expels the extra vitamin B-12 it does not use through your urine. While it is unusual to have high B-12 levels in your blood, a dietary supplement may raise those levels. However, current research does not indicate that high levels of B-12 are dangerous.
Effects of B-12
Your body needs vitamin B-12 for several important functions. According to the Linus Pauling Institute, when in your body, B-12 is used in two key forms: methylcobalamin and 5-deoxyadenosyl cobalamin. These forms are necessary for the metabolic process that converts the food you eat into energy you can use. B-12 also participates in red blood cell production, the synthesis of hemoglobin -- the compound that carries oxygen in your red blood cells -- and supporting neurological health.
Normal Range
According to the National Institutes of Health, doctors can determine your levels of B-12 through blood testing. The lowest amount considered healthy is between 120 to 180 picomoles of the vitamin per liter of blood. Currently, there is no cap or tolerable upper limit of B-12 in your blood and body since research has not yet discovered any negative effects.
Excess
High levels of B-12 are not known to be toxic to humans. According to the Linus Pauling Institute, doses even as high as 1 mg daily have not been shown to cause problematic side effects. Even though you make take high doses of B-12 orally, your body only absorbs what it needs, leaving the rest to be filtered out by your kidneys and expelled through your urine. This may cause your urine to be slightly cloudy, but this will cease when you stop taking the supplement.
Deficiency
You need to get at least 2.4 mcg of vitamin B-12 daily. If you are an adult older than 51 years of age, your body may naturally have trouble absorbing the vitamin, so you should get your B-12 through a supplement or fortified foods. A B-12 deficiency can inhibit your body's production of red blood cells, causing a condition called anemia, in which your blood cannot carry enough oxygen throughout your body. You can also suffer neurological damage, causing numbness in your limbs, disorientation and dementia.
