Fat-Soluble vs Water-Soluble

Vitamins fall into two camps based on how your body stores them. Fat-soluble vitamins (A, D, E, K) dissolve in fat and can sit in your liver and fatty tissue for weeks or months. That storage is also why you can overdose on them if you megadose supplements.

Water-soluble vitamins (C and all the B vitamins) dissolve in water. Your body uses what it needs and flushes the rest out in urine, so you need a steady daily supply. It also means those expensive vitamin C megadoses mostly produce expensive urine.