Is vitamin D fat-soluble or water-soluble? I’m trying to understand how vitamin D is absorbed and stored in the body, specifically relating to dietary intake and supplementation. Does its solubility affect how often I need to take it, how much can be absorbed at one time, and whether it’s possible to overdose on it compared to water-soluble vitamins?

Answer

Vitamin D is a fat-soluble vitamin. This means it dissolves in fats and oils and can be stored in the body’s fatty tissues and liver.

The absorption of vitamin D from the gut is enhanced when it is consumed with dietary fat. Because it’s fat-soluble, it’s absorbed along with fats in the small intestine. From there, it’s transported via chylomicrons through the lymphatic system and into the bloodstream.

Unlike water-soluble vitamins, fat-soluble vitamins like vitamin D are not readily excreted in urine. This characteristic allows them to accumulate in the body, potentially leading to toxicity if consumed in excessive amounts over a prolonged period. However, the body’s ability to store vitamin D also means that it doesn’t need to be consumed daily as consistently as water-soluble vitamins. The body can draw upon its stores of vitamin D when dietary intake is insufficient.