Cod-liver oil is derived from the fresh liver of the cod (Gadus callarius). It is a rich source of vitamin D, used in the prevention and treatment of RICKETS, and of vitamin A. Human milk contains more than enough vitamin D for the breast-fed baby, provided the mother has a balanced diet with adequate exposure to sunlight, or is taking vitamin supplements during pregnancy and lactation if considered necessary. All baby foods in the UK contain added vitamins, and therefore supplementation is unnecessary until weaning begins, and the baby starts taking cow's milk, which contains less vitamin D than human milk. (See APPENDIX 5: VITAMINS.)