Vitamins: Deficiency Diseases & Classification

CHENucleic Acids & Vitamins

Vitamins are accessory food factors, classified by solubility into fat-soluble (A, D, E, K) and water-soluble (B-complex, C). This subtopic is almost entirely recall: matching each vitamin to its deficiency disease and explaining the dietary-frequency difference by solubility.

Fat-soluble vitamins are A, D, E, K; water-soluble are the B-complex group and vitamin C.
Fat-soluble deficiencies: A gives night blindness (and xerophthalmia); D gives rickets in children / osteomalacia in adults; E gives reproductive/muscular weakness (sterility, increased RBC fragility); K gives delayed blood clotting (impaired coagulation).
Water-soluble deficiencies: $B_1$ (thiamine) gives beri-beri; $B_6$ (pyridoxine) gives convulsions; niacin ( $B_3$ ) gives pellagra; $B_{12}$ gives pernicious anaemia; C (ascorbic acid) gives scurvy.
Water-soluble vitamins must be taken regularly because they are not stored — excess is excreted in urine; fat-soluble vitamins are stored in fatty tissue and liver, so are not needed every day.
Excess fat-soluble vitamins can accumulate to toxic levels (hypervitaminosis) precisely because they are stored, unlike the readily excreted water-soluble vitamins.
Quick clues: vitamin A prevents night blindness; vitamin D is synthesised in skin on exposure to sunlight; vitamin C prevents scurvy; vitamin K is required for blood clotting.
Vitamins are organic compounds required in tiny amounts that the body cannot (mostly) synthesise; they regulate metabolism (acting as coenzymes) and must be supplied in the diet.
Vitamin $B_3$ (niacin / nicotinamide) deficiency causes pellagra (the '3 Ds': dermatitis, diarrhoea, dementia).
Chemical names worth knowing: vitamin C = ascorbic acid, $B_1$ = thiamine, $B_2$ = riboflavin, $B_3$ = niacin, $B_6$ = pyridoxine, $B_{12}$ = cyanocobalamin.
Vitamin $B_2$ (riboflavin) deficiency causes cheilosis (cracking of lips) and a sore tongue/skin; the B-complex vitamins act largely as coenzymes in metabolism.
Mnemonic for fat-soluble: 'A, D, E, K' — these dissolve in fats/oils and are absorbed and stored with dietary lipids.
Because water-soluble vitamins are not stored, deficiencies appear relatively quickly, whereas stored fat-soluble vitamins can take longer to become deficient but also risk toxicity in excess.

Where the marks go

Putting vitamin C among the fat-soluble group — C and all the B vitamins are water-soluble; only A, D, E, K are fat-soluble.
Confusing rickets (vitamin D, children) with scurvy (vitamin C) or with beri-beri (vitamin $B_1$ ) — match the vitamin to the right disease.
Saying fat-soluble vitamins must be eaten daily — they are stored, so they need NOT be taken every day; it is the water-soluble ones that must be replenished regularly.
Assigning pellagra to the wrong B vitamin — pellagra is the deficiency of niacin (vitamin $B_3$ ), not $B_1$ or $B_{12}$ .
Forgetting that excess fat-soluble vitamins are toxic precisely because they accumulate, while excess water-soluble vitamins are simply excreted.

How the board asks it

Define / statevitamin-to-disease mapping; solubility class
Name the vitamin whose deficiency causes (i) night blindness, (ii) scurvy and (iii) rickets, and state in each case whether the vitamin is fat-soluble or water-soluble.
Distinguishfat-soluble (A, D, E, K) vs water-soluble (B-complex, C)
Distinguish between fat-soluble and water-soluble vitamins, giving one example and one deficiency disease of each class.
Structure / namingdeficiency disease to vitamin
A person shows symptoms of pellagra (dermatitis, diarrhoea and dementia). Name the vitamin that is deficient and state whether it is fat-soluble or water-soluble.
Give reasonsstorage vs excretion by solubility
Give a reason why water-soluble vitamins such as $B_1$ and C must be supplied regularly in the diet, whereas fat-soluble vitamins need not be taken every day.
Define / statechemical names of vitamins
Give the chemical name of vitamin C and of vitamin $B_1$ , and name one deficiency disease associated with each.

Practise this topic

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Written for Sublevo. Question text quoted anywhere in these notes is the Council’s and carries its year and paper; the board’s own diagrams are not reproduced.