Which vitamin is not produced and stored in organisms?

Vitamin C is unique among the vitamins listed because it is not produced or stored by the body. While the body can synthesize vitamins A, D, and K to varying degrees and can store them for later use, vitamin C, also known as ascorbic acid, must be obtained entirely from the diet. This is because humans, unlike many animals, lack the enzyme required to synthesize vitamin C from glucose.

As a water-soluble vitamin, any excess vitamin C that is consumed is excreted in urine, making it essential for individuals to regularly intake vitamin C-rich foods such as fruits and vegetables. This is especially important for maintaining overall health since vitamin C plays critical roles in collagen synthesis, immune function, and as an antioxidant.

In contrast, vitamins A, D, and K can be stored in the liver and fatty tissues of the body, allowing for reserves to be drawn upon when dietary intake is not sufficient.