New Zealand and iodine deficiency: Lessons learned

Studies conducted in the early part of the 20th century found that urinary iodine excretion of NZ residents, an index of iodine intake, was much lower than that reported in nearby Pacific Islands or parts of Australia. The introduction of iodised table salt in 1939 improved iodine status and reduced goiter rates by the early 1950s. In the 1960s the dairy industry began using iodophors, further increasing iodine intakes. However, in the 1980s a decline in the use of iodised table salt, the replacement of iodophors by non-iodine containing disinfectants and an increase in the use of non-iodised rock salt, resulted in a re-emergence of mild iodine deficiency in the early 1990s. In 2009, the NZ government introduced the mandatory fortification of bread with iodised salt as a public health strategy to alleviate iodine deficiency. Fortifying a limited number of foods in a sequential manner (i.e. salt and then bread) may decrease iodine-induced hypothyroidism, a condition that occurs when iodine intakes are increased after a long period of iodine deficiency. Recent data in NZ suggests that the fortification of bread has modestly improved iodine status, but those who eat little or no bread do not benefit. In 2010, the government recommended all pregnant women take an iodine supplement to meet their increased requirements, however, the efficacy and effectiveness of this strategy, in addition to bread fortification, has not been investigated. New Zealand's story illustrates how government strategies and changing food patterns can impact on iodine status.