Selenium deficiency occurs when an organism lacks the required levels of selenium, a critical nutrient in many species. Deficiency, although relatively rare in healthy well-nourished individuals, can have significant negative results, affecting the health of the heart and the nervous system; contributing to depression, anxiety, and dementia; and interfering with reproduction and gestation. Signs and symptoms
Selenium deficiency in combination with Coxsackievirus infection can lead to Keshan disease, which is potentially fatal. Selenium deficiency also contributes (along with iodine deficiency) to Kashin-Beck disease. The primary symptom of Keshan disease is myocardial necrosis, leading to weakening of the heart. Kashin-Beck disease results in atrophy, degeneration and necrosis of cartilage tissue. Keshan disease also makes the body more susceptible to illness caused by other nutritional, biochemical, or infectious diseases. Selenium is also necessary for the conversion of the thyroid hormone thyroxine (T4) into its more active counterpart triiodothyronine (T3), and as such a deficiency can cause symptoms of hypothyroidism, including extreme fatigue, mental slowing, goiter, cretinism, and recurrent miscarriage. Causes
It can occur in patients with severely compromised intestinal function, those undergoing total parenteral nutrition, those who have had gastrointestinal bypass surgery, and also in persons of advanced age (i.e., over 90).People dependent on food grown from selenium-deficient soil may be at risk for deficiency.
Increased risk for developing various diseases has also been noted, even when certain individuals lack optimal amounts of selenium, but not enough to be classified as deficient.For some time now, it has been reported in medical literature that a pattern of side-effects possibly associated with cholesterol-lowering drugs (e.g., statins) may resemble the pathology of selenium deficiency. Diagnosis
Reference ranges
The European Food Safety Authority (EFSA) recommends a dietary allowance of 70 μg per day selenium intake for adults. In the US, the Dietary Reference Intake for adults is 55 µg/day. In the UK it is 75 µg/day for adult males and 60 µg/day for adult females. 55 µg/day recommendation is based on full expression of plasma glutathione peroxidase. Selenoprotein P is a better indicator of selenium nutritional status, and full expression of it would require more than 66 µg/day. Epidemiology and prevention
Selenium deficiency is uncommon, but regions in China, Europe, Russia and New Zealand have low levels of selenium in croplands and diet. The worldwide prevalence of selenium deficiency is however predicted to rise under climate change due to the loss of selenium from croplands. These diseases are most common in certain parts of China where the intake is low because the soil is extremely deficient in selenium. Studies in Jiangsu Province of China have indicated a reduction in the prevalence of these diseases by taking selenium supplements. In Finland, selenium salts are added to chemical fertilizers, as a way to increase selenium in soils. Dietary supplements may utilize sodium selenite, L-selenomethionine or selenium-enriched yeast.