The number of countries where iodine deficiency is a public health problem has halved over the past decade, shows the new report, but deficiency is still a significant cause of mental developmental problems in children in 54 countries.
"Iodine deficiency is a major threat to the health and development of people worldwide, particularly preschool children and pregnant women," said Dr Lee Jong-wook, WHO director-general.
He added that the goal of eliminating iodine deficiency ?by universal salt iodization - around the world is within reach and called for this to be achieved by 2005.
Deficiency results when the soil is poor in iodine, causing a low concentration in food products and insufficient iodine intake in the population.
When iodine requirements are not met, the thyroid may no longer be able to synthesize sufficient amounts of thyroid hormone. The resulting low-level of thyroid hormones in the blood is the principal factor responsible for the series of functional and developmental abnormalities, leading to poor school performance, reduced intellectual ability and impaired work capacity.
Globally, UNICEF estimates that 66 per cent of households now have access to iodized salt.
The problem of iodine deficiency was most severe in Africa, while in Europe only Albania has moderate to severe deficiency.
Europe, however, had the highest number of countries of different world regions where the problem was reported as mild, with Russia and the Ukraine among 15 problem cases.
And in 29 nations iodine intake was too high, which could result in iodine-induced thyroid dysfunction, WHO said.