Some 760 million people have goitres, the swelling of the thyroid gland in the neck that is the most common and visible sign of iodine deficiency. The successful global campaign to iodize all edible salt is reducing the risk of iodine deficiency, which threatened 1.6 billion people as recently as 1992. About 12 million infants born in 1996 were spared that risk thanks to iodized salt, and the number of babies born cretins is estimated to have dropped by more than half, from 120,000 in 1990 to under 55,000 worldwide. Over 100 million young children suffer from vitamin A deficiency. It is a contributing factor in the 2.2 million deaths each year from diarrhoea among children under five and the nearly 1 million deaths from measles.
Severe deficiency can also cause irreversible corneal damage, leading to partial or total blindness.
Results of a dozen field trials in Brazil, Ghana, India, Indonesia, Nepal and elsewhere indicate that supplementing the diets of children at risk of vitamin A deficiency can reduce deaths from diarrhoea. Four studies showed deaths were reduced by 35-50 per cent. The vitamin can also reduce by half the number of deaths due to measles. Vitamin A capsules cost roughly 2 cents each. Supplementation reduces the risk of death of a child deficient in vitamin A by 23 per cent.