Vitamin B12, also known as cobalamin, is the most complicated vitamin, structurally, and is also the largest. Cobalamin is water soluble and travels through the bloodstream. As with most water soluble vitamins, the body is able to excrete any excess from the vitamin. At the same time the human body stores several year's worth of cobalamin (Cbl) in the liver, so nutritional deficiency of this vitamin is not common, though it can occur. What interested a group of scientists, led by Johan Arendt of the Department of Clinical Biochemistry of Aarhus University Hospital in Denmark, was the opposite of B12 scarcity in the body, they wanted to investigate cases where an overabundance of this vitamin existed. Could high levels of Cbl be linked to cancer, as some past studies have suggested?
To assess high Cbl levels and risk of cancer, Arendt and his colleagues used Danish Medical registries to review the records of 333,667 patients without cancer who had been referred for Cbl testing. A normal range of vitamin B12 is considered to be somewhere between 200 and 600 pmol/L (pico mole per liter, a standard measurement unit for blood work). First, the researchers excluded any patients who were receiving Cbl therapy or who had a cancer diagnosis before the study began. Next, they estimated the incidence of cancer in this population between 1998 through 2010. Finally, they isolated six percent with Cbl levels greater than the upper reference limit (greater than or equal to 601 pmol/L).
What did the researchers discover? “High plasma Cbl levels increased the risk of subsequently diagnosed cancer, mostly within the first year of follow-up,” wrote the authors. “However, this association was not present for all cancer types.”
Specifically, the risk of cancer increased among those patients whose levels were greater than 800pmol/L. Among those with abnormally high Cbl levels, the risks were particularly elevated for hematological (blood) and smoking- and alcohol-related cancers, such as those affecting the liver, colon, and lungs. The researchers also found that after five years of follow-up, risks remained high for anyone with a level greater than 800pmol/L.
Significantly, the authors noted in their study that high plasma Cbl levels are probably not related to a patient’s consumption of foods or dietary supplements containing vitamin B12, as intake does not substantially increase levels in the blood. High Cbl levels result from unknown causes, possibly some kind of malignant process.