Animated Solution for Chemistry - Organic Chemistry: Which among the following pair of vitamins is stored in our body relatively for longer duration ?

When we think about vitamins, we often wonder why some need to be taken daily while others do not. The answer lies entirely in their chemical nature, specifically their solubility.

Vitamins are broadly classified into two major categories: fat-soluble and water-soluble. This simple classification dictates how our body processes, stores, and excretes these essential nutrients.

The Body's Reserves

Fat-soluble vitamins are those that dissolve in fats and oils. The primary examples in this category are Vitamins A, D, E, and K. A simple mnemonic to remember them is the word KEDA.

Because these vitamins are soluble in lipids, our body can easily absorb them along with dietary fats. More importantly, the body can store them in the liver and in adipose (fat-storing) tissues.

Due to this storage capability, fat-soluble vitamins remain in the body for a relatively longer duration. This means we do not necessarily need to consume them every single day, as the body can tap into its reserves when needed.

The Daily Requirement

On the flip side, we have water-soluble vitamins. These include the B group vitamins (such as Thiamine, Riboflavin, etc.) and Vitamin C (chemically known as Ascorbic acid).

Since these vitamins dissolve in water, they are not easily stored in the body's tissues. Any excess amount consumed is readily filtered by the kidneys and excreted through urine.

Because they are constantly flushed out, water-soluble vitamins must be supplied regularly through our daily diet. (Note: Vitamin $B_{12}$ is a unique exception, as it can be stored in the liver for years despite being water-soluble).

Armed with this knowledge, let's evaluate the options provided in the question. We are looking for a pair of vitamins that is stored in our body for a longer duration, which means both vitamins in the pair must be fat-soluble.

- Option (a): Thiamine (Water-soluble) and Vitamin A (Fat-soluble). - Option (b): Vitamin A (Fat-soluble) and Vitamin D (Fat-soluble). - Option (c): Thiamine (Water-soluble) and Ascorbic acid (Water-soluble). - Option (d): Ascorbic acid (Water-soluble) and Vitamin D (Fat-soluble).

Looking closely at the choices, only Option (b) contains a pair where both vitamins are fat-soluble. Both Vitamin A and Vitamin D are stored in the liver and adipose tissues, allowing them to remain in the body for a much longer duration compared to their water-soluble counterparts.

Therefore, the correct answer is Option (b).