This study provides further information on the prevalence of thyroid dysfunction and autoimmune thyroid diseases in an iodine sufficient area. In addition, it suggests that more than half of the patients with unsuspected hypothyroidism were negative for autoantibodies and that the excessive iodine intake may be involved in causing latent hypothyroidism.

The prevalence of thyroid dysfunction in relation to iodine intake was studied in adults (n = 1061) in five coastal areas of Japan that produce iodine-rich seaweed (kelp). The prevalence of hyperthyroidism (TSH < 0.15 mU/L) was similar in these areas, whereas that of hypothyroidism (TSH > 5.0 mU/L) varied from 0-9.7%. The relative frequency of above normal iodide concentration in the morning urine (> or = 75 mumol/L) [high urinary iodide (UI)] varied from 3.7%-30.3%. Together with previously reported results of a noncoastal city, the frequency of high UI correlated significantly with that of hypothyroidism with negative thyroid autoantibody (r = 0.829, n = 6, P < 0.05) but not with positive thyroid autoantibody (r = 0.278, NS) or with that of hyperthyroidism (r = 0.038, NS). Hypothyroidism was more prevalent in thyroid autoantibody-negative subjects with high UI (group II, 12.1%) than with normal UI (group I, 2.3%) (P < 0.001). The TSH [21.9(6.5-73.7)mU/L] (mean +/- SD) and thyroglobulin [288 (182-456) micrograms/L] levels in group II were significantly higher than the respective levels in group I [9.6(3.7-25.3)mU/L and 123 (38-399) micrograms/L] (P < 0.05). Free T4 of group II (9.9 +/- 3.9 pmol/L) was significantly lower than in group I (14.2 +/- 3.9 pmol/L) (P < 0.05). These results indicate that 1) the prevalence of hypothyroidism in iodine sufficient areas may be associated with the amount of iodine ingested; 2) hypothyroidism is more prevalent and marked in subjects consuming further excessive amounts of iodine; and 3) excessive intake of iodine should be considered an etiology of hypothyroidism in addition to chronic thyroiditis in these areas.

Abstract. To assess the daily iodine intake in a population study, we have compared the validity and degree of reliability of the urine iodide/creatinine ratios and iodide concentrations of casual samples as a representative index of daily urine iodide excretion. The morning urine samples were obtained from apparently healthy 2,956 men and 1,182 women residing in Sapporo, Japan, and urine iodide was measured by an iodide selective electrode. The iodide/creatinine ratio was higher in women than in men, increasing more steeply with age in women than in men, due to a concomitant decrease in the urine creatinine level with age. The iodide concentration showed no age-related change. Similarly the daily urine iodide excretion measured in 22 control subjects by collecting 24-h urine specimens did not vary with age, while the iodide/creatinine ratio of these subjects increased with age. The correlation coefficient(r) of the iodide concentration with daily iodide excretion in the 95 observations of the 22 subjects was 0.832 (P<0.001), higher than that of iodide/creatinine ratio with daily iodide excretion (0.699, P<0.001). The 95% range of the iodide concentration in morning urine samples in the population (n=4,138) was 9.0-70.3 µmol/L with a mean of 27.1 µmol/L. These results indicate that in a population with a large difference in age, an age-associated decrease in the urine creatinine concentration should be considered for the evaluation of the iodide/creatinine ratio and the measurement of the iodide concentration in morning spot urine sample may also be useful for the estimation of daily iodide excretion, and that the Japanese subjects here have a high iodine intake, with considerable variation. nient procedure especially in large population studies, and it has been suggested that the ratio between the concentration of iodine and creatinine in casual urine samples shows the daily urinary excretion of iodine [1][2][3] . It has been shown that urinary creatinine excretion varies with age, sex, body size, and the nutritional state [4][5][6], and these factors might have a strong influence on the iodine/creatinine ratio.We have conducted screening for thyroid diseases, and intended to investigate the possible

Ten patients with primary hypothyroidism (aged 32--66 yr), replaced on constant daily doses of L-T4 (mean +/- SD, 1.90 +/- 0.22 micrograms/kg BW), were used to examine seasonal variations in serum levels of thyroid-related hormones for a period of 14 months. Basal and peak TSH concentrations after TRH (500 micrograms) were higher in winter than in summer. Summer values for basal TSH were all normal (normal range, less than 4.8 microU/ml), while winter values were supranormal in 5 of 10 patients. Summer values for peak TSH were subnormal or normal (normal range, 5.0--40.0 microU/ml), while winter values were supranormal in 3 patients, with the remaining values being normal [log basal TSH, 0.511 +/- 0.438 vs. 0.084 +/- 0.244 (P less than 0.05); log peak TSH, 1.394 +/- 0.410 vs. 1.017 +/- 0.423 (P less than 0.05)]. Serum resin T3 uptake, T4, free T4 index(FT4I), T3, free T3 index, and rT3 levels did not vary seasonally, although T4 and FT4I tended to fall in the winter. The summer and winter QKd interval (the interval from the onset of a QRS complex in the electrocardiogram to the appearance of the Korotkoff sound at diastolic pressure), basal metabolic rate, and serum cholesterol concentrations were all within the normal range. Basal and peak TSH after TRH were inversely correlated with serum T4 and FT4I levels. The basal TSH concentration was further inversely correlated with the seasonally altering ambient temperature. These results indicate that during the treatment of primary hypothyroidism with constant doses of T4, 1) serum TSH and its response to TRH show seasonal variation, 2) the hypersecretion TSH in the winter is related to small changes in serum T4 and FT4I levels, and 3) the seasonal variation in the serum TSH concentration may need to be taken into consideration when evaluating the adequacy of a T4 replacement dose.

The case of a 38-year-old woman with left thyroid hemiagenesis associated with the right aortic arch is presented. The diagnosis of hemiagenesis was established by isotopic and ultrasonic imaging, and also by angiographically defined absence of the left thyroid arteries. The aortogram revealed a right aortic arch with isolation of the left subclavian artery from the aorta. Although the significance and mechanism of the concomitant development of these anomalies is unknown, this case may be the first report in the literature.