Adverse Health Effects of Selenium in Humans

Epidemiologic studies and case reports from 24 years ago indicated that chronic exposure to selenium compounds was linked to several adverse health effects in humans. Early toxic effects included impacts on endocrine function, particularly affecting thyroid hormone synthesis at dietary exposures of around 300 micrograms Se/d, and the metabolism of growth hormone and insulin-like growth factor-1. Selenium exposure could also impair natural killer cell activity and, at higher levels, cause hepatotoxicity and gastrointestinal disturbances. Dermatologic effects such as nail and hair loss and dermatitis were observed after high environmental selenium exposure. Long-term exposure posed challenges in assessing toxicity and morbidity, with potential neurotoxicity, including motor neuron degeneration and increased risk of amyotrophic lateral sclerosis. Selenium species exhibited a bivalent effect on cancer risk, either increasing or decreasing it. The environmental selenium exposure limits at the time were deemed inadequate for preventing adverse health effects.