Vitamins

Deficiency of vitamin $B_{12}$ causes pernicious anaemia (RBC deficient in haemoglobin).

Vitamin $B_1$ is thiamine; its deficiency causes beri-beri (loss of appetite, retarded growth).
Sterility is linked to vitamin E, convulsions to vitamin $B_6$ and cheilosis to vitamin $B_2$ deficiency.

Vitamins are classified by their solubility in water or fat.
Fat soluble vitamins: A, D, E and K; they are soluble in fats and oils, insoluble in water, and are stored in the liver and adipose tissue.
Water soluble vitamins: the B group vitamins and vitamin C; they are readily excreted in urine and cannot be stored (except vitamin $B_{12}$).
Hence vitamin B complex is not a fat soluble vitamin.

Vitamins are classified into two groups on the basis of their solubility.
Fat soluble vitamins: vitamins A, D, E and K. They are soluble in fats and oils but insoluble in water, and are stored in the liver and adipose tissue.
Water soluble vitamins: the B group vitamins and vitamin C. They must be supplied regularly in the diet because they are readily excreted in urine and cannot be stored in the body (except vitamin $B_{12}$).
So vitamin B is water soluble, whereas vitamins A, E and K are water insoluble.

Vitamins are organic compounds required in small amounts for normal growth and health.
Most vitamins cannot be synthesised by the human body, so they must be supplied in the diet; that is why they are called essential dietary factors.
(Only a few are made in limited amounts, for example vitamin D in the skin in sunlight.)
DNA is synthesised in every dividing cell by replication.
Hormones are produced by the endocrine glands.
Enzymes are proteins synthesised in the cells of the body.
So the human body does not produce vitamins.