Lack of iodine linked to no-salt ethos

By ALISON HORWOOD

A generation of New Zealanders who obeyed doctor's orders by cutting back on salt are now beginning to suffer from an iodine deficiency.

A survey commissioned by the Ministry of Health shows a sample of 307 schoolchildren aged between 8 and 10 had either a mild or moderate iodine deficiency.

Only 2 per cent had sufficient thyroid levels at those set down by the World Health Organisation.

Extreme iodine deficiency can cause goitre, a swelling of the thyroid gland, and may contribute to impaired intellectual performance, lethargy and hearing loss.

Because of their physical and mental growth, children are the hardest-hit.

The modern trend to leave iodised salt off the dinner menu is one contributor to the problem. Scott Coulter, a spokesman at Dominion Salt, says iodine is added only to free-flowing table salt and not rock salt.

In New Zealand, iodine occurs naturally in significant amounts only in fish and seafood. In most countries, small amounts are found in crops and meat, but New Zealand has iodine-deficient soil. Some farmers provide livestock with iodine-rich mineral blocks.

The survey, carried out by Associate Professor Christine Thomson, Sheila Skeaff and Rosalind Gibson at the department for human nutrition at Otago University, showed the median amount was 6.6 micrograms of iodine per deci-litre of urine. A score under 10 is considered a mild deficiency.

"Salt may no longer be effective, and other options for increasing dietary iodine should be explored," says the report.

The results will go to the Ministry of Health's Food and Nutrition Advisory Committee and be forwarded to the Director-General of Health, Dr Karen Poutasi.

A leading Auckland-based nutritionist, Dr John Birkbeck, agrees the Government must investigate a new vehicle for iodine because salt has become a "dirty word," associated with hard arteries and heart disease.

"So many people limit their salt intake we may need to give serious consideration to what else we can add it to. Perhaps other foods, such as bread, can be looked into."

Because of an epidemic of goitre, the Government in 1924 chose salt to deliver iodine to the nation. Iodine was added in the form of potassium iodide at between 40 and 80 milligrams a kilogram - a level which has not changed - and goitre was wiped out overnight.

In a peculiar twist, scientists say the essential nutrient was also lost when New Zealand gave up glass milk bottles and began to use ammonia products to clean dairy vats.

Until the 1980s, iodine chemicals used in the cleaning contaminated the milk and boosted iodine levels.

Present and much-publicised health regulations prevent iodine being added to any other product, so it is not found in processed foods such as potato chips and bread. In other countries it is added to the water supply or cooking oil.

Dr Birkbeck said the results of mild deficiencies were difficult to gauge, and more research needed to be carried out. "We can only assume, however, that if someone is getting less of a nutrient than what they need, it will become a problem, even if it is not easy to measure."

Otago University professor John Mann said a 1990-91 survey estimated the typical New Zealand adult diet contained between 94 and 109 units of iodine, well under the recommended amount of 120 to 150 units. "The simplest way to avoid iodine deficiency is to ensure that what salt we do have is iodised," said Dr Mann.