Vitamin B12 is important for nervous system such as brain, spinal cord, nerve and also for red blood cell. Long term deficiency will bring about side effects related to these parts of your body.
However, the amount which Vitamin B12 required by the body is not in large quantity and it can be stored in the body (for a longer time) and being reused.
If one is a lacto-ovo-vegetarian, one will have no problem with having enough Vitamin B12 because it is available from eggs, yoghurt, cheese, soya and etc.
According to ADA (American Dietetic Association), Vitamin B12 cannot be found from plant-based food sources. Therefore, for pure vegetarian, the following options must be considered.
1.) Consume food supplement.
Bee Pollen is a good choice of natural food supplement for Vitamin B12.
2.) Consume food and beverages which contain Vitamin B12 such as soya and breakfast cereal.