The Iodine Content of Foods, Manures and Animal Products in Relation to the Prophylaxis of Endemic Goitre in New Zealand: Studies from the Universiaaty of Otago, New Zealand
Authors: Hercus C. E. , Roberts K. C. 
Published: May 2009

The correlation of high goitre incidence in New Zealand with low soil iodine having been established previously, the distribution of iodine in its relationship to the goitre problem is further considered in this study. The method of analysis used throughout has been that of Th. V. Fellenberg, with certain minor modifications. The findings are summarised as follows:

1. In a general survey of the iodine content of foodstuffs in New Zealand, it has been shown that the foods richest in iodine, arranged in descending order of iodine content, are edible seaweed, sea fish, eggs, wholemeal cereal products, leafy vegetables and milk. Refined cereal products, root vegetables, and fruits are shown to be of low iodine content. Dried foods contain more iodine than the corresponding fresh foods.

2. A comparative study of the iodine content of foodstuffs from goitrous and non-goitrous districts establishes the fact that the soil-iodine is accurately reflected in the food-iodine.

3. The difference in the daily iodine intake in the food supply of typical goitrous and non-goitrous districts is calculated to be 14·35 micrograms.

4. The iodine content of certain vegetables and animal foods is shown to present a well-marked seasonal variation. The maximum iodine content of vegetable matter is reached in the late autumn and winter when growth is at a minimum. In the case of eggs the maximum is reached in summer, in milk in the spring. In the latter case calving and lactation are shown to be disturbing factors of importance.

5. Cooking is shown to have little effect on the reduction of the iodine content of root vegetables, seaweed, fish and bread, but to reduce the content of green vegetables by about two-thirds.

6. Commercial salt is shown to be an unreliable source of iodine supply, the majority being practically iodine-free.

7. Tobacco smoke is a negligible source of iodine supply.

8. The iodine content of the artificial manures commonly used in New Zealand is determined, and their probable effect on the content of crops is calculated.

9. The iodine adsorptive powers of different types of soils is estimated experimentally. Loam is shown to have marked retentive powers for soluble iodides. In clay the retention is less and in sand nil.

10. Experimental studies on the influence of iodine-rich manures on plant life are presented.

11. A well-defined relationship is shown to exist between goitre incidence and iodine excretion in the urine.

12. The iodine content of human milk in the goitrous woman is shown to be lower than in the non-goitrous, and a relationship is shown to exist between the amount of iodine excreted in the urine and milk during lactation.

13. The flesh of fish is shown to vary in iodine content according to its “iodine environment.”

14. Small amounts of potassium iodide added to the diet of various animals is shown to increase the iodine content of the thyroid glands and of the food products.

15. Certain intestinal bacteria are studied in regard to their power of absorbing iodine from an alkaline medium rich in iodine with negative results.

16. Certain data with regard to the iodine content of the thyroid glands of various animals are submitted which suggest that certain animals can live on a lower iodine threshold than man without developing goitre.