This study was carried out from 1972-1974, in order to elucidate the protein-binding iodine (PBI) revels in sera and their seasonal variations in inhabitants of Okinawa. Subjects number and experimental duration were approximately the same as those of Report 7 concerning the basal metabolic rate (BMR).
During the first year, subjects included 26 males native to Okinawa (15 in summer and 11 in winter) (Group O) and 27 natives of the main Japanese island (20 in summer and 7 in winter) (Group M). During the second year, subjects included 19 males native to Okinawa and 14 native to other places. The same subjects were examined both in summer and winter. To measure PBI, blood samples were drawn from the cubital vein when the BMR measurements of Report 7 were carried out and Faulkner's alkaline calcination method, revised by Itoga et al. was employed.
Results obtained were as follows;
1) Significant differences were not found in serum PBI levels between Groups O and M.
2) PBI values in Okinawa inhabitants showed seasonal changes that were smaller in summer and greater in winter. However, there was no significant difference in the rate of change between the two groups.
3) In summer, significant differences were found in Okinawan subgroups, lower for office workers than for Maritime Self-Defence Force personnel and student police. The difference seemed to be due to at least in part to the environmental temperatures at the respective place of work and to the degrees of physical activity each job requires.
4)The mean PBI values for all inhabitants of Okinawa, i.e, 5.2μg/dl in August and 6.1μg/dl in January, were compared with those for inhabitants in Sasebo and Nagasaki cities, reported by Kuwano et al. and Tsuchimoto respectively. The values for the main islands were 3.2μg/dl and 4.9μg/dl in summer, and 7.1μg/dl and 7.4μg/dl in winter for Self-Defence Force personnel in Sasebo and civilians in Nagasaki respectively. Though there were no seasonal BMR changes, significant seasonal PBI changes were found in inhabitants of Okinawa but much greater ones for Nagasaki and Sasebo inhabitants.
5) PBI values in August were almost the same for both Okinawa and Nagasaki inhabitants. The temperature in August was almost the same in both regions. However, FBI values in January in Okinawa were lower than those in October and the same as those in April for the inhabitants in Nagasaki and Sasebo, at which times temperatures are almost the same as in Okinawa in January.
From previous studies in Nagasaki and Sasebo, it has been found that serum PBI changes seasonally proceeding that of BMR and is higher in cooler seasons than in warmer ones. Therefore, it is thought that the above PBI differences in both seasons would be less in the Okinawans where temperature changes during a year are much slower and less than those in Nagasaki and Sasebo. Thus the seasonal change of BMR in Okinawans, almost the same as that of inhabitants elsewhere, occures under the condition of smaller seasonal changes in PBI values in the former group.
