Evidence that cassava ingestion increases thiocyanate formation: A possible etiologic factor in endemic goiter

In inhabitants of Ubangi (an endemic goiter area in Zaire) with severe iodine deficiency, serum and urinary thiocyanate (SCN) concentrations (1.06 and 1.92 mg/100 ml) were higher (P < 0.001) than levels observed in Belgian controls (0.22 and 0.60 mg/100 ml, respectively). Among the Ubangi population, the urinary SCN levels rose with thyroid hyperplasia, and variations with age and sex were comparable to the curve of goiter distribution. In 30% of the patients, the serum SCN level was over 1 mg/100 ml, above which value SCN inhibits the iodide pump in persons with a normal iodine intake. An intensive cassava diet during 3 days significantly raised serum and urinary SCN concentrations in patients with low levels at the outset, stopping the diet decreased these concentrations in patients with high levels at the outset. A large cassava meal raised urinary iodide excretion from 9.3 to 18.1 μg/day (P < 0.001) and reduced131I thyroidal uptake in girls of a Ubangi boarding school (P < 0.05). In two groups of adolescents with a similar iodine deficiency (urinary iodide excretion 13.5 and 11.5μg/day), subjects with a high serum SCN level (1.06 mg/100 ml) had lower serum thyroxine (P < 0.01) and higher TSH (P < 0.001) levels than subjects with low serum SCN levels (0.26 mg/100 ml). These data suggested that the thiocyanate exposure in Ubangi was linked with the consumption of cassava and played a decisive part in the etiology of endemic goiter. In such conditions of chronic thiocyanate overload, adjustment to the iodine deficiency was achieved only through a greatly enhanced thyrotropic stimulation, probably intended to compensate for inhibition of the iodine transport mechanism by thiocyanate. © 1978 by The Endocrine Society.