Anecdotal side effects of vitamin B-12 overdose include congestive heart failure and the gathering of fluid in the lungs, although research is necessary to prove these claims, notes Health Central. Because vitamin B-12 has a safe reputation, as of 2015, little research has explored the risks of overdose.
Vitamin B-12 is important for overall wellness. It helps the nervous system retain its health, facilitates normal energy levels and is important in the synthesis of DNA. In the digestive tract and bone marrow, it plays a key role in cellular metabolism. Supplementation is necessary for a number of conditions, including those who have undergone weight loss surgery and who have difficulty absorbing nutrients. Discussing proper dosage with a physician is crucial, reports Health Central.