How can vegans and vegetarians prevent vitamin B12 deficiency? What can result from vitamin B12 deficiency?

http://www.veganmainstream.com/2010/12/24/feature-interview-the-truth-about-food-with-dr-michael-greger/

VM: How can vegans and vegetarians prevent vitamin B12 deficiency? What can result from vitamin B12 deficiency?

MG: It’s so easy! All you have to do is get a regular source of B12, and there are only two ways to get it: fortified foods and supplements. One 2,000 microgram tablet of vitamin B12 once a week is all you need. B12 deficiency can lead to all sorts of terrible things, including psychiatric, intestinal and neurological problems as well as paralysis and death. It’s something that can’t be ignored, but it’s something that’s very easy to take care of.