Why can fat-soluble vitamins build up in the body?

Fat-soluble vitamins—vitamins A, D, E, and K—can build up in the body because they are stored in fatty tissue and the liver, rather than being readily excreted in the urine like water-soluble vitamins.12

Because these vitamins are soluble in fat, the body retains them for longer periods, meaning they do not need to be consumed daily to meet nutritional requirements. However, this capacity for storage also increases the risk of toxicity if they are consumed in excessive amounts over time, as the body cannot easily eliminate the surplus. While the body has mechanisms to break down and excrete certain vitamins—for instance, vitamin A is processed and excreted in bile and urine, and vitamin D is excreted in feces—the accumulation in tissues remains a primary characteristic of this group.21