Vitamins are either water-soluble or fat-soluble. But what does that really mean...
Here's the deal. When you take a vitamin supplement that is water-soluble, your body metabolizes what it can and flushes out the excess through pee. Your body does not store theses vitamins so it is important to get them daily through diet or a supplement. Vitamin C, vitamin B2 (Riboflavin), and vitamin B9 (Folic Acid) are all water-soluble.
Unlike water-soluble vitamins that need regular replacement in the body, fat-soluble vitamins are stored in the liver and fatty tissues, and are eliminated much more slowly than water-soluble vitamins. You also need a little fat in your diet to absorb fat-soluble vitamins. Vitamins A, D, E, and K are fat-soluble. Since these vitamins are stored in the body, you generally don't need to take supplements of them. You can actually create a toxic build up - oh my!
Fit's Tips: If you are taking supplements, make sure you're not taking more of the water-soluble ones than your body can absorb at one time. If you do, you're literally flushing your money down the toilet.