H.—3l

i nV estia:ated this problem. He found the use of iodized salt to be but 20 per cent, of the i ' V nJnmntion Thames is the scene of an extensive fishing industry, and lodme-rich fishes to be widely used in the dietary. Table VIII shows the iodine content of some varieties of fish from Thames.

Table VIII.-The Iodine Content of Fish from Thames.

Watson was unable to detect the operation of any other factor which would account for the low goit 7n TlbleYll Clydevale would appear to be anomalous in that it has a higher goitre incidence than the level of urinary iodine excretion would suggest. However, the possibility of errot and the disturbing influence which iodine medication and seasonal variation may have on iodine metabolism render it necessary to interpret the result with caution. Until this district is re-examined it will be necessary to suspend judgment. Chapter VI. —Prophylaxis. (a) Consumption of lodized Salt.-The history of goitre prophylaxis in New Zealand was reviewed bv Hercus and Purves (1936). The importations of iodized salt showed a slow rise up to 1934, when thev were equivalent to 1-82 gm. per head of population per day, estimated at less than 30 per cent, of the total domestic salt-consumption. The extent to which iodized salt is used varies considerably from district to district. The results of some recent inquiries are shown m lable 1 .

Table IX.

It is apparent that for New Zealand as a whole the result is unsatisfactory and that a much greater utilization of iodized salt would be necessary to make prophylaxis effective. (b) Level of lonization.—There is as yet no general agreement as to the level ol iodine supplementation necessary to maintain the health of the thyroid gland. Table X gives the standards for- iodized salts in different countries and illustrates the wide differences in supplementation which prevail.

Table X.

From the data in Chapter V it is apparent that there is a wide difference m iodine intake between goitrous and non-goitrous countries. It is plain that goitre prophylaxis cannot be expected to be satisfactory unless the supplementation raises the urinary iodine excretion to the level found m nongoitrous countries. In New Zealand even with the present use of iodized salt the level is 100 micrograms per day below this level. We have found the average daily ingestion of domestic salt m New Zealand o be 5 »rams to 6 grams per head per day. At the present level of supplementation this would supply micrograms to 37 micrograms. It is evident that even if 100 per- cent, utilization of iodized salt were to obtain the supplementation would be grossly inadequate. The exact amount of supplementation necessary to raise the excretion by 100 micrograms depends on the proportion of the iodine intake excreted in the urine, which is at present unknown. Until th b information is available and the exact relationship of urine examination to total iodine intake determined

107

Variety. Iodine Content. Trevalli • • '' micrograms/kilo fresh weight. Kahawai .. • • • • • ■ " Snapper .. .. •• •• " «°0 Pipi .. ■ • ■ • • • '■ 51U

District. Observer. | Percentage. Cromwell .. • • " " on 'rViamps . . ■ ■ ■ • Watson (1936) . ■ • • «« f'isborne •• Burnard and McGeorge (1937) i 68 New Plymouth .. Lomas and Law (1937) ..! 14 Westport .. • • Foote (1938) .. . Plunket Society .. • ■ I Irwin (1937) .. • •

[ . 1 Micrograms Country. j Supplementation. i iodine, per Gram. Switzerland .. .. 1 1 part of potassium iodide/200 000 .. .. •• 3-8 Norway and Sweden .. I 1 part of potassium iodide/80,000 » ° Miehiean U.S.A. .. 1 part of sodium iodide/10,000 •• •• •• ' OQ New Zealand 1 part to 2 parts potassium or sodium iodide/250,000 .. 3-1 to 6-8