A cluster of thyrotoxicosis associated with consumption of a soy milk product.

OBJECTIVE To determine whether a New Zealand cluster of thyrotoxicosis with low uptake on scintiscan was associated with soy milk consumption. METHOD A case-control study was conducted, with controls matched by age, sex, and region. RESULTS All cases (5/5) and one control (1/30) consumed soy milk before the index date. The cases all drank a brand of soy milk that had unexpectedly high levels of iodine. In a simple unmatched unadjusted analysis, the lower bound of the 95% confidence interval for the odds ratio was 19. CONCLUSION This cluster was associated with consumption of a soy milk product. The thyrotoxicosis was probably due to iodine-induced thyrotoxicosis. IMPLICATIONS This investigation raises issues about quality control in manufacturing processes and the monitoring of food products for their safety. It also raises issues about public and health professional awareness of the potential health effects from food additives in some processed foods.