Vitamin B12 is water-soluble, which means that the body will only use what it NEEDS from food/supplements and the rest...well you'll pee it out basically. There is really no major risk about taking "high" levels of water-soluble vitamins (unless you have some kind of medical problem related to them that could potentially interfere with absorption/excretion). Also, because of its nature as water-soluble, you have to continuously supply it in your diet (or via supplement). Your body can't store it up for future use (only the few fat-soluble vitamins are capable of being stored- Vit A, D, E and K).
However, I wouldn't recommend taking a supplement that has more than the 100% DV (or RDA?) you need each day. What that is, I don't know off the top of my head, but your body can only use so much at a time--the rest is wasted (and money down the drain).
SparkPeople, SparkCoach, SparkPages, SparkPoints, SparkDiet, SparkAmerica, SparkRecipes, DailySpark, and other marks are trademarks of SparkPeople, Inc. All Rights Reserved. No portion of this website can be used without the permission of SparkPeople or its authorized affiliates.
SPARKPEOPLE is a registered trademark of SparkPeople, Inc. in the United States, European Union, Canada, and Australia. All rights reserved.