Particularly in developing countries, people whose staple diet is cereals or cassava are dangerously low in micronutrients such as iron, zinc, iodine and Vitamin A. The most serious dietary deficiencies are: protein-calorie malnutrition (because of its high mortality rate, its wide prevalence and the irreversible physical and mental damage it may cause); xerophthalmia, vitamin A deficiency, (because of its contribution to mortality of malnourished children, its relatively wide prevalence and the dramatic irreversible damage it causes, namely blindness); nutritional anaemias, iron deficiency anaemia and megaloblastic anaemias (because of their wide distribution, their contribution to mortality from many other conditions and their effects on working capacity); endemic goitre, iodine deficiency, (because of its wide distribution). In some specific areas of the world, other nutritional problems such as beriberi, vitamin B1 deficiency; pellagra, nicotinic acid deficiency associated with protein deficiency; or rickets, vitamin D deficiency, may be of considerable importance.