Vitamin B12, or cobalamin, is important for the development of healthy red blood cells and proper nervous system function. The main dietary sources of vitamin B12 include meat, dairy and fish. While doctors are often more concerned with low vitamin B12 levels, high levels might also signal a serious medical problem. Elevated blood levels of vitamin B12 are generally associated with increased amounts of proteins that carry vitamin B12 in the bloodstream or release of stored vitamin B12.
Excess Vitamin Supplements
The most obvious cause of an elevated vitamin B12 level is taking too much of the vitamin in the form of supplements. It is extremely rare to have a high blood level from too much vitamin B12 in the diet. While vitamin B12 is generally not considered toxic in high levels, it's important to determine if the elevation is due to excess vitamin supplements since other causes of a high vitamin B12 level are usually serious.
Leukemia and Related Blood Diseases
High vitamin B12 levels are associated with many blood diseases, including various types of leukemia and related blood disorders. According to a September 2012 study in "PLoS One," people with high vitamin B12 had a 4- to 18-times higher risk of having a blood disease. Chronic myeloid leukemia is one such disease, in which the elevated vitamin B12 levels are thought to be due to release of excess B12 carrier proteins from the cancerous white blood cells. Other blood disorders have also been associated with high levels of vitamin B12, including polycythemia vera, myeloproliferative syndrome, acute leukemia, eosinophilia and eosinophilic leukemia. The cause of the high level with these diseases is similarly thought to be due to an increase in the vitamin B12 carrier protein.
Solid Organ Cancers
An elevated vitamin B12 level can be a nonspecific indicator of several types of solid organ cancer. A June 2013 review article published in the "Quarterly Journal of Medicine" reported that high vitamin B12 levels most commonly occur with liver cancer. Other cancers that might cause an elevated B12 level include lung, breast, colon, stomach, pancreas, kidney and possibly prostate cancer. It is thought that excess production of vitamin B12 carrier proteins by the tumors is the primary culprit for elevated levels. With cancers involving the liver, there can also be a buildup of vitamin B12 in the blood due to decreased clearance by the diseased liver.
The liver is the main storage and clearance site for vitamin B12. High blood B12 levels can occur in liver conditions such as cirrhosis and hepatitis. Alcoholic liver disease is an example of a liver condition associated with high vitamin B12. With alcoholic liver disease, vitamin B12 as well as its carrier proteins can be elevated. One of the main causes of increased vitamin B12 with liver disease is release of stored vitamin by liver cells that have died due to the disorder. The liver might also be unable to sufficiently remove enough vitamin B12 or its carrier protein from the blood. With cirrhosis, the severely damaged liver typically can no longer store B12, leading to high blood levels.
An increased blood level of vitamin B12 is sometimes caused by kidney disease, including diabetic kidney disease. There are a few different ways kidney disease is thought to contribute to high blood vitamin B12 levels. Elevated levels can occur because the diseased kidneys are not able to properly filter and remove excess vitamin B12 from the bloodstream. High vitamin B12 levels could also be explained by elevated vitamin B12 binding protein levels that are not filtered properly by the kidneys.