Bright yellow urine is common when taking a multivitamins, due to the B2 vitamin, which is known as riboflavin. In fact, “flavin” comes from the Latin “flavus” which means yellow.
B vitamins are water soluble, which means they can dissolve in water, so they’re not stored in the body like many other nutrients. Water soluble nutrients need daily replenishment, so it’s important to consume a good supply each day. Throughout the day, your body will excrete some of the vitamin that it doesn’t absorb, which can lead to that lovely bright yellow urine.
Just because you’re excreting some of your B-vitamins through urination doesn’t mean that your body isn’t absorbing them. Instead, it indicates that your body is just taking what it needs at the time.