Thyroid function changes related to use of iodinated water in the US SpaceProgram

Background: The National Aeronautics and Space Administration (NASA) has us ed iodination as a method of microbial disinfection of potable water system s in U.S. spacecraft and long-duration habitability modules. A review of th yroid function tests of NASA astronauts who had consumed iodinated water du ring spaceflight was conducted. Methods: Thyroid function tests of all past and present astronauts were reviewed. Medical records of astronauts with a diagnosis of thyroid disease were reviewed, iodine consumption by space cr ews from water and food was determined. Serum thyroid-stimulating hormone ( TSH) and urinary iodine excretion from space crews were measured following modification of the Space Shuttle potable water system to remove most of th e iodine. Results: Mean TSH significantly increased in 134 astronauts who h ad consumed iodinated water during spaceflight. Serum TSH, and urine iodine levels of Space Shuttle crewmembers who flew following modification of the potable water supply system to remove iodine did not show-a statistically significant change. There was no evidence supporting association between cl inical thyroid disease and the number of spaceflights, amount of iodine con sumed, or duration of iodine exposure. Conclusions: It is suggested that ph armacological doses of iodine consumed by astronauts transiently decrease t hyroid function, as reflected by elevated serum TSH values. Although advers e effects of excess iodine consumption in susceptible individuals are well documented, exposure to high doses of iodine during spaceflight did not res ult in a statistically significant increase in long-term thyroid disease in the astronaut population.