Soil selenium and human health in China

Selenium (Se) is a naturally occurring metalloid element which is essential to human health in small doses (deficiency level < 0.04 μg/day,) but can be toxic in excess ( > 900 μg/day). Se plays a vital role in many metabolic functions and is an essential component of the biologically important glutathione peroxidase (GSH-Px) antioxidant enzymes. In China, Se deficiency has been linked to an endemic degenerative heart disease known as Keshan Disease (KD) and an endemic osteoarthropathy which causes deformity of affected joints, known as Kaschin-Beck Disease. Selenium deficiency has also been implicated in the onset of oesophageal cancer. Se toxicity (selenosis) is less widespread and causes hair and nail loss and disorders of the nervous system. Although these diseases had been linked to environmental Se levels by previous investigators, it was not clear why some villages suffered Se deficiency or Se toxicity diseases whereas others in close proximity did not.