Vitamins — Classification & Deficiency Diseases

What Vitamins Are

Certain organic compounds are required in only small amounts in our diet, but their deficiency causes specific diseases. These compounds are vitamins. NCERT defines them as organic compounds required in the diet in small amounts to perform specific biological functions for the normal maintenance of optimum growth and health of the organism.

Most vitamins cannot be synthesised in our body, so they are treated as essential food factors. Plants can synthesise almost all of them, and the bacteria of the gut can produce some required by us; the rest must come from the diet. Vitamins are designated by alphabets — A, B, C, D — and some are further split into sub-groups such as $\text{B}_1$, $\text{B}_2$, $\text{B}_6$ and $\text{B}_{12}$. Different vitamins belong to different chemical classes, so they cannot be defined by structure; their common thread is functional, not structural.

The name itself records a historical correction. The term "Vitamine" was coined from vital + amine, because the first compounds identified carried amino groups. Later work showed that most of them did not contain amino groups, so the trailing "e" was dropped — and the modern spelling vitamin remains. Excess of vitamins is also harmful, which is why NCERT cautions that vitamin pills should not be taken without a doctor's advice.

Classification by Solubility

Because vitamins share no common structure, they are classified on a physical property — their solubility in water or fat. This single criterion splits all vitamins into two groups and, as we will see, controls how they are stored, how readily they are lost, and how often they must be eaten.

Fat-Soluble vs Water-Soluble

Fat-soluble vitamins are soluble in fats and oils but insoluble in water. This group contains vitamins A, D, E and K. Because they dissolve in fat, they are stored in the liver and in adipose (fat-storing) tissue, giving the body a reserve.

Water-soluble vitamins — the B-group vitamins together with vitamin C — dissolve in water. They are readily excreted in urine and cannot be stored in the body, with the single exception of vitamin B₁₂. The mnemonic worth committing to memory is simply "the fat-soluble four": A, D, E, K. Everything else (B-group and C) is water-soluble.

The NCERT Source & Deficiency Table

The single most exam-relevant block of this section is NCERT Table 10.3, which lists important vitamins with their dietary sources and the diseases caused by their deficiency. The table below reproduces those entries exactly. Master the vitamin → deficiency-disease column first, then the sources; NEET match-the-list questions are built directly from it.

Fat-Soluble Vitamins in Detail

The fat-soluble four are absorbed alongside dietary fat and lodged in fatty stores, which means a steady reserve but also a real risk of toxicity in excess. Their deficiencies, read straight from Table 10.3, are tightly defined.

Vitamin A deficiency produces xerophthalmia, a hardening of the cornea of the eye, and night blindness; its sources are fish liver oil, carrots, butter and milk. Vitamin D, obtained from exposure to sunlight, fish and egg yolk, prevents rickets — bone deformities in children — and osteomalacia, the softening of bones and joint pain seen in adults. Vitamin E, from vegetable oils such as wheat germ and sunflower oil, guards against increased fragility of RBCs and muscular weakness. Vitamin K, found in green leafy vegetables, keeps blood clotting time normal; its deficiency lengthens that clotting time.

Water-Soluble Vitamins in Detail

The water-soluble group is the B-group plus vitamin C. Within the B-group, NEET focuses on four members. Vitamin B₁ (thiamine) — from yeast, milk, green vegetables and cereals — prevents beri beri, characterised by loss of appetite and retarded growth. Vitamin B₂ (riboflavin), sourced from milk, egg white, liver and kidney, prevents cheilosis (fissuring at the corners of the mouth and lips) along with digestive disorders and a burning sensation of the skin. Vitamin B₆ (pyridoxine), from yeast, milk, egg yolk, cereals and grams, prevents convulsions. Vitamin B₁₂ — meat, fish, egg and curd — prevents pernicious anaemia, in which red blood cells are deficient in haemoglobin.

Vitamin C (ascorbic acid) is the lone non-B water-soluble vitamin in the table. Its sources are citrus fruits, amla and green leafy vegetables, and its deficiency causes scurvy, marked by bleeding gums. Among all water-soluble vitamins, only B₁₂ can be stored in the body — every other member of this group, including vitamin C, must be replenished continually.

Why Storage Differs — and Why It Matters

The solubility split is not a bookkeeping detail; it directly governs how the body handles each vitamin. Fat-soluble vitamins dissolve in the lipid stores of the liver and adipose tissue, so the body keeps a reserve and intake can lapse for a time without immediate deficiency. Water-soluble vitamins dissolve in body water and are continuously filtered into urine, so they are flushed out rather than banked.

This is exactly why NCERT states that water-soluble vitamins must be supplied regularly in the diet — there is no reserve to draw on. The one carve-out is vitamin B₁₂, the sole water-soluble vitamin the body can store. The standard NCERT exercise "Why cannot vitamin C be stored in our body?" turns on this very point: vitamin C is water-soluble and is excreted in urine, so it is not retained and must be eaten regularly.

The NEET Angle

In NEET, vitamins almost always appear as direct recall or match-the-list items, and the answer is decided entirely by the NCERT table. The 2025 paper, for example, asked candidates to match B₁₂, D, B₂ and B₆ with pernicious anaemia, rickets, cheilosis and convulsions respectively — every link lifted from Table 10.3. The 2021 paper asked which vitamin's deficiency causes "RBC deficiency," answered by B₁₂ (pernicious anaemia).

The reliable preparation is therefore mechanical: lock the vitamin → deficiency-disease pairs, then the sources, and finally the solubility-and-storage rule. If the disease names and the "fat-soluble four" are memorised cleanly, this section is essentially a guaranteed mark.