How can I tell if a vitamin is effective?

I just started taking a vitamin mutil .. im taking Shaklee Vita Lea. Vitamin mutil with added minerals and iron. someone told me that taking vitamins is a waste of time because it goes right through you before your body becomes even vitamins. Is this true? and if this is true for some vitamins and not others how do I know?

Well, I've never used to take vitamins and I found myself tired and get sick more often then I started to take the advice would probably not need of them .. but I find it more easy to just take vitamin and eat ok and not have to read all the stuff on the label .. GOOD LUCK stay healthy and what you decide .. I figure they
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