Vitamin B12 is an important and complex compound that plays an active part in development of red blood cells and is also critical for maintaining the health of the nerve tissues. Deficiency of B12 can result in problems like anemia along with nerve as well as brain damage. Other problems caused by deficiency of B12 vitamin include pernicious anemia, weight loss, menstrual problems and increased susceptibility to infections. Lack of adequate sources of vitamin B12 is one of the low B12 causes. B12 being a complex compound cannot be produced by animals or plants. In fact it is largely dependent on the ability of these animal and plant sources to store this vitamin and their inter-relationship with the micro-organisms like bacteria. Since animals tend to store this vitamin in greater amounts, animal sources are rich in Vitamin B12. Those primarily depending on vegan or vegetarian diet tend to suffer from low Vitamin B12 levels as they do not get enough sources providing this Vitamin.

The levels of Vitamin B12 within the body are also dependent on another factor, called the intrinsic factor which is a special protein developed within the body. This intrinsic factor is critical since it has to be present so as to bind with Vitamin B12 and thereby help in the absorption process. In case of conditions like pernicious anemia, the body may not be able to create this intrinsic factor and so the absorption of Vitamin B12 may become inadequate and this is one of the low B12 causes. Such problems of malabsorption of Vitamin B12 can occur if a person has undergone surgery to remove part of stomach and this adversely affects the ability of the body to digest food. In case of other problems like Crohn's disease and Celiac disease, the bacterial growth in small intestine may be adversely affected and this in turn may affect the ability of the body to absorb this Vitamin. Elderly individuals also tend to experience this problem as with aging the gastric acid production of the body may undergo changes and this may result in malabsorption.

Use of certain medicines may also result in deficiency of Vitamin B12. For example, Use of metformin which is a medication for diabetes may interfere with absorption of Vitamin B12. Other reasons for low B12 causes can also be intestinal infestation by certain parasites or other organisms like fish tapeworm. This may use the Vitamin B12 for itself depleting the B12 levels in the body. Excess growth of certain bacteria in the small bowel may affect with the ability of the body to absorb Vitamin B12. Dependence on alcohol or alcohol abuse on a chronic basis can also result in low levels of Vitamin B12. Abuse of nitrous oxide can also result in deficiency of Vitamin B12. Through diagnosis of low B12, the right kind of solution for the problem can be determined. Following identification of a possible deficiency, correction of the same can be done through consumption of food sources rich in Vitamin B12 or by starting Vitamin B12 supplementation.