Vitamin B12 does not accumulate to toxic levels. Consuming large quantities does not cause side effects or high levels in your system, whether you get it through food or from taking high-dose supplements. High vitamin B12 in the bloodstream is associated with serious diseases. Medical conditions that can increase levels of vitamin B12 include liver disease, kidney failure and a group of blood cancers known as myeloproliferative disorders, which includes myelocytic leukemia and a condition that causes an overgrowth of red blood cells called polycythemia vera. Hypereosinophilic syndrome, a medical condition marked by too many white blood cells, also can cause high vitamin B12.High vitamin B12 is a symptom of an underlying illness that causes the amount in your blood to increase. For example, a damaged liver may release the vitamin out of storage and into the blood. In early stages, illnesses associated with high vitamin B12 often have generic symptoms, such as fatigue and loss of appetite. Considering they’re potentially life-threatening conditions, early diagnosis is vital, so consult your physician when you don’t feel up to par. Blood tests are the only way to verify whether high vitamin B12 is present; excessive amounts alone won’t cause any signs.high levels of vitamin B12 have been associated with cancers of the liver, breast, gastrointestinal tract, kidney and possibly prostate. cirrhosis and hepatitis may be possible.