ADEK: absorbed with fat, stored in the body, and capable of toxicity
Mnemonic
ADEK, the four fat soluble vitamins:
- A - retinol. Deficiency causes night blindness, xerophthalmia and Bitot’s spots
- D - calciferol. Deficiency causes rickets and osteomalacia
- E - tocopherol. Deficiency causes haemolysis and a spinocerebellar syndrome
- K - phylloquinone. Deficiency causes bleeding, with a prolonged prothrombin time
Because they need bile and micelles for absorption, all four are deficient together in fat malabsorption: coeliac disease, cystic fibrosis, cholestasis, pancreatic insufficiency and after ileal resection or orlistat.
They are also the four that can be toxic in excess, since they are stored rather than excreted: vitamin A causes raised intracranial pressure and is teratogenic, vitamin D causes hypercalcaemia.
Expansion
A, D, E and K share four properties that set them apart from the water soluble vitamins:
- Absorbed with dietary fat, requiring bile salts and pancreatic lipase
- Carried on lipoproteins
- Stored in liver and adipose tissue
- Capable of toxicity in excess
Deficiency therefore occurs together in fat malabsorption: cholestasis, pancreatic insufficiency, coeliac disease, cystic fibrosis, short bowel and orlistat use.
| Vitamin | Active form and role | Deficiency | Excess |
|---|---|---|---|
| A | Retinal for vision, retinoic acid for differentiation | Night blindness, xerophthalmia, Bitot spots | Teratogenic, raised intracranial pressure, hepatotoxicity |
| D | Calcitriol; calcium absorption | Rickets, osteomalacia | Hypercalcaemia, stones |
| E | Antioxidant, protects membranes | Haemolysis, ataxia, neuropathy | Bleeding, antagonises vitamin K |
| K | Cofactor for gamma-carboxylation of factors II, VII, IX, X, C and S | Bleeding, prolonged PT | Rare |
Vitamin A in pregnancy deserves emphasis: retinoids are among the most potent human teratogens, which is why liver and retinoid drugs are avoided and why strict contraception is required with isotretinoin.