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Thyroid Disease Investigated Among LSAH Population (LSAHNEWSV7_1_1)
Research Area:
Clinical medicine
Species Studied
Scientific Name: Homo sapiens Species: Human

Iodine is used for microbial disinfection in the potable water systems of U.S. spacecraft. Because iodine is metabolically active within the body, there is concern about chronic exposure to iodine in drinking water aboard U.S. spacecraft.

Iodine is an essential micronutrient. It is present in food and water predominantly as iodide. It is rapidly and almost completely absorbed, with the excess excreted in urine. Iodide is transported to the thyroid gland where it is used to synthesize and secrete the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which act at multiple sites throughout the body and help to regulate metabolic processes. The activity of the thyroid is regulated by a negative feedback mechanism involving the pituitary gland and the hypothalamus. Thyrotropin releasing hormone (TRH) is released by the hypothalamus and provokes the pituitary to secrete the thyroid stimulating hormone (TSH), which is also known as thyrotropin. TSH stimulates the thyroid gland to release its hormones and to trap iodide. The thyroid hormones in turn inhibit the release of both TRH from the hypothalamus and TSH by the pituitary, in this way maintaining normal plasma levels of the thyroid hormones.

A deficiency of iodine can lead to a wide spectrum of diseases ranging from severe cretinism with mental retardation to barely visible enlargement of the thyroid. Endemic goiter and the more severe forms of iodine deficiency disorders are a worldwide issue. Providing an adequate iodine intake can prevent iodine deficiency disorders. The recommended daily allowance of total iodine is 0.15 mg/day. Dietary sources of iodine include seafood, water from coastal areas, and iodized salt. Plant and animal sources vary depending on the soil, fertilization, feeding of animals, and food processing. The iodine intake by the majority of the US population is considered to be adequate and safe.

The potential chronic toxic effects of excessive iodine are of current concern with respect to the astronaut population. Goiter and thyrotoxicosis have been documented in areas of Japan and Tasmania where dietary intake of iodine was exceptionally high. In populations where the drinking water has been disinfected with iodine, reported associations of iodine and thyroid disease are mixed. Some studies have reported weak, but significant, associations and other studies have reported no associations. Generally, iodine intakes of up to 2 mg/day have caused no adverse physiological reactions in healthy adults, but that level may be too high to sustain over long periods of time.

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National Aeronautics and Space Administration. Thyroid disease investigated among LSAH population. In: Longitudinal Study of Astronaut Health Newsletter. February 1998;7(1):1.

Thyroid hormones
Thyroid gland

Data Information
Data Availability
Archive is complete. All data sets are on the Web site.
Data Sets + View data.

Thyroid disease prevalence
Thyroid stimulating hormone (TSH)

Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
LSAH 01/01/1989 05/31/2010 21 years

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Jessica Keune
Institutional Support
National Aeronautics and Space Administration (NASA)