THE THYROID STATUS OF THE YANOMAMO INDIANS OF SOUTHERN VENEZUELA - 1992 UPDATE

Previous reports described an apparent paradox in the clinical express ion of endemic iodine deficiency in Amazonian Indians, who were severe ly iodine deficient but had no goiter and were clinically euthyroid. T o confirm and explain this unique observation, we estimated the iodine intake and evaluated the functional and structural thyroid status of an isolated population of Yanomamo Indians (n = 104) in southern Venez uela. Twenty-six children, 32 adolescents, and 46 adults were studied with serum thyroid function tests, spot urinary iodide concentration d eterminations, and sonographic measurement of thyroid gland volume. A subset of adolescents and adults (n = 35) had 24-h fractional thyroida l I-131 uptake determinations. No individual with goiter, clinical hyp othyroidism, or cretinism was observed. Children had higher mean serum T4 (114.5 vs. 102.9 nmol/L; P < 0.02) and serum T3 (2.96 vs. 2.46 nmo l/L; P < 0.02) concentrations than adults, with 2% and 50%, respective ly, of children having levels more than 2 SD above the mean for a Nort h American reference population. Serum TSH concentrations were also hi gher in children than adults (3.3 vs. 2.3 mU/L; P < 0.02), with 25% of the subjects above the reference range. Mean urinary iodide was 61 +/ - 29 mug/L (range, 10-178 mug/L), reflecting borderline iodine suffici ency. Thyroidal I-131 uptake values were 28 +/- 7%, with 33% above the upper limit of normal (30%). Compared to an iodine-replete Swedish po pulation, the thyroid gland volume was above normal (>mean +/- 2 SD) i n 71 % of the study children. We conclude that the Yanomamo have borde rline iodine deficiency, associated in children with predictably highe r serum T3 and TSH concentrations and a high prevalence of small goite rs. The basis for the apparent change in their dietary iodide intake o ver the past 30 yr is unclear, as is the explanation for their previou sly postulated resistance to goitrogenesis with more profound iodine d eficiency.