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Re-emergence of iodine deficiency in NZ

Over recent years there has been increasing concern about the re-emergence of iodine deficiency in New Zealand. The iodine deficiency disorder (IDD) goiter was considered endemic in many parts of New Zealand prior to the 1940s. Following the introduction of iodised salt in the 1950s, the rate of IDD goiter was reported to have fallen to approximately 1%.

The re-emergence appears to be due to:

  • Increased consumption of commercially-prepared foods – these are mostly manufactured with non-iodised salt.
  • Declining use of iodophors as sanitisers by the dairy industry – it is thought ‘contamination’ of milking equipment provided a significant source of iodine.
  • Less salt being used in home prepared foods as a response to the public health advice to reduce salt intake. Sea salt and rock salt are being used more frequently (encouraged by popular chefs) and these are not iodised.

Therefore, this begs the question: “Should iodine levels be considered in patients with hypothyroidism?”

Urinary iodine estimations are unreliable for assessing individual patients, as urinary levels can vary considerably from day to day and are therefore not useful. The main role of urinary iodine excretion levels is for epidemiological studies to provide a relatively accurate estimate of the dietary iodine status of a particular population.

Most cases of primary hypothyroidism in developed countries are caused by chronic autoimmune lymphocytic thyroiditis, ablative therapy for Graves’ disease, or inadequate thyroid replacement therapy.

It is probably best that iodine nutrition is addressed as a public health issue.

References:

Jones NT. Diagnosis and management of hyperthyroidism and hypothyroidism. MJA 2004;180:541-542
Mann J, Aitken E. The re-emergence of iodine deficiency in New Zealand? NZ Med J 2003;116(1170):U351