Seasonal Changes in Iodine Metabolism

Publisher Website
Google Scholar
Abstract
The iodine content of samples of liquid and dried milk from Yorkshire and Scotland was measured during the years 1959-63. A definite seasonal fluctuation was apparent. The concentration of iodine in liquid milk rose during the early months of the year to a maximum of about 20 [mu]g/100 ml in March and April. Thereafter it declined to a minimum value of about 1 [mu]g/100 ml in August and September. It rose slowly during the last three months of the year. A similar variation occurred in dried milk. The iodine content of the foodstuffs supplied to cows throughout the year on a Sheffield farm was measured in relation to the changes in the milk. The large seasonal change was due to the feeding during the winter months of cattle cake to which iodine had been added in large amounts. It is suggested that the supplement given to the cows in winter should be retained throughout the whole year. The daily excretion of iodine in the urine was measured over a week in 29 healthy subjects on unrestricted diets. Considerable variation was evident from day to day and little reliance could be placed on a single 24-hour collection. The mean urinary iodine excretion correlated closely with the weight of the subject. Approximately 60% of a single supplement of 500 [mu]g- of iodine taken by mouth was recovered in the urine. A meal of sea fish might increase urinary iodine excretion, but the effect was variable owing to wide differences in the iodine content of fish. A seasonal change in excretion of iodine was apparent; the amount excreted declined during the summer, so that in the period July to September it was not quite half that encountered during the winter. This decrease was due to the fall in the concentration of iodine in milk during the summer months and demonstrated the importance of milk as a source of iodine in the diet.