If you are thinking about becoming vegan you have likley done some research into the vegan lifestyle and diet to determine what foods you should eat, any road blocks that might be in your way, and if there are any special nutrition aspects you should be concerned about. While many omnivores will argue that vegans can't possibly get enough protein or other essential nutrients for a healthy body, that argument has come under fire in recent months and more people now understand that most vegans eat more than the recommended daily amount of protein via legumes and leafy greens.
Since the protein argument has lost some of the wind out of its sails, omnivores have now taken to claiming that a vegan diet must be unhealth and unnatural because there is no reliable source of the vitamin B12 in the vegan diet. In this case, the omnivores and critics are correct: there is no naturally occuring source of B12 in a vegan diet. What they fail to acknowledge, however, is the fact that B12 is not a naturally occuring vitamin in animal products either.
B12 is a water soluble vitamin that helps maintain normal brain and central nervous system function. While B12 is found in animal products, it is only because animals consume B12 from the food they eat that is contaminated with B12 from the soil where a type of bacteria creates the vitamin. Omnivores will generally point out that a B12 deficiency can be catastrophic, causing fatigue, depression, and poor memory (and can lead to more serious illnesses), however, the actual amount of B12 needed to keep our brain and central nervous system healthy is very minimal.
So little B12 is needed for day-to-day purposes that even though we only store 2-5 milligrams, that can actually last us for up to 3 years! B12 deficiencies are very rare, and even though when they do occur they are serious, it is not as much of a health concern as most vegan objectors would have you believe.
While it's good to know that we do not need much B12 to stay healthy, it's important that we take optimal care of our bodies by consumming enough B12 to meet our daily needs. Fortunately, getting enough B12 in your diet is easy and doesn't necessarily require the use of a multi-vitamin or supplement either. Nutritional yeast, a product normally found in the refrigerated section of your health food store, is usually fortified with B12 (be sure to check the label) and many breakfast cereals and granola bars are fortified with B12 as well - enough to get you many times more than your recommended daily intake (an excess of B12 is not harmful to the body).
If you are still concerned about getting enough B12 in your diet you can take either a small daily B12 supplement or a 2000 microgram supplement each week - though most multi-vitamins have quite a lot of B12 as well. For a long list of fortified places you can get B12, see the PCRM website. While it used to be possible to get B12 from vegetables, most cleaning processes rob the veggies of the vitamins that occur on the exterior, therefore it's no longer a reliable source of B12.
If you are still thinking about if becoming vegan is the right choice for you, know that by eating a well-rounded diet you will get all of the essential vitamins and minerals you need to have to maintain optimal health. If you are interested in learning more about the vegan lifestyle, there are many books and websites that have a wealth of information on any topic related to veganism you can imagine.