Type of Papers: Reports completed by expert consultations and published by the World Health Organization jointly with the Food and Agriculture Organization of the United Nations (FAO).
Note: Two WHO reports were summarized together as they contain much of the same information. See references below.
- There are two types of selenium-containing enzymes (i.e., selenoproteins):
- The first group of enzymes is involved in the antioxidant defense system, protecting against oxidative damage during stress, infection, or tissue injury and helping to maintain immune defenses to infection.
- The second group of enzymes is required for normal thyroid functioning and is important for growth and development.
Prevalence of Deficiency:
- The prevalence of selenium deficiency is not known due to insufficient data. Severe deficiency has been reported in regions of China, Japan, Korea, New Zealand, Scandinavia, and Siberia.
Risk Factors for Deficiency:
- Living in regions with low selenium content in the soil.
- Low intakes of animal products.
- Presence of Keshan disease or Kaschin-Beck disease (see below).
- More sensitive biochemical markers of selenium status are needed. Currently, the best biochemical marker is serum selenium.
- Monitoring the selenium content of the diet is also recommended.
Dietary Sources and Bioavailability:
- The selenium content in food depends on the soil conditions in which the food is grown or raised. Certain types of soils contain matter that binds selenium making it unavailable to crops and pasture grasses. Thus, selenium deficiency rates vary depending on geographic region.
- Regions with poor selenium soil content and therefore an increased risk for selenium deficiency include:
- China: regions from northeast to southwest China (Keshan disease is endemic)
- The Transbaikalia region of southern Siberia
- Regions in northern Europe, including some areas of Finland and the United Kingdom
- Some areas of New Zealand
- Meat is a good source of selenium because animals increase their intestinal absorption of selenium when their intake of the nutrient is low due to poor soil content. This increase in absorption helps to maintain normal levels of selenium even when there is little selenium in the soil.
- Older infant formulas have contained insufficient amounts of selenium to meet infant requirements. It is recommended that infant formulas contain a minimum of 10µg/day, but no more than 45µg/day.
Recommended Nutrient Intakes (µg/day): The following are the Recommended Nutrient Intakes (RNI) as defined by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization.
- Clinical manifestations of selenium toxicity include hair loss, changes to hair and nails, yellow-tinted skin, and gastrointestinal disturbances. Dental carries have also been reported.
- The tolerable upper limit (UL) for selenium in children ages 1-3 years is 90 µg/day.
- On a community level, effective interventions have included the use of selenium-rich fertilizers and the importation of cereals from areas with high levels of selenium in the soil.
- Various foods worldwide are currently fortified with selenium, including salt, sports drinks, and infant foods. For example, selenium fortification of table salt has reduced the prevalence of Keshan disease in China.
Health Consequences of Deficiency and Benefits of Intervention:
- Health Consequences of Deficiency:
- Clinical manifestations due to non-endemic selenium deficiencies (e.g,. low infant formula content, long-term parenteral or enteral feeding) are not very common and are poorly understood. Symptoms have included muscular weakness, myalgia (muscle pain), and congestive heart failure.
- Severe deficiency can cause Keshan disease or Kaschin-Beck disease:
- Keshan disease is endemic in children between the ages of 2 and 10 years living in regions of China with low soil selenium availability. Selenium deficiency is the primary factor in contracting this disease, making children susceptible to the disease. Selenium supplementation prevents contracting the disease. However, selenium supplementation after the disease is established does not alleviate the condition. Symptoms include fatigue after mild exercise, loss of appetite, cardiac arrhythmia, cardiac insufficiency, and congestive heart failure.
- Kaschin-Beck disease is a bone and joint disease due to selenium deficiency in preadolescent and adolescent children (e.g., between of 5 and 13 years of age). It is found in regions of China, Siberia, Japan, and Korea.
- Selenium deficiency seems to increase susceptibility to viral infections
- Impaired thyroid functioning:
- Thyroid function may be affected in infants with mild selenium deficiency.
- In regions with endemic cretinism associated with iodine deficiency and impaired thyroid functioning, poor selenium soil content has also been observed. More research is needed to understand the effectiveness of screening for selenium deficiency and supplementing with selenium when treating iodine deficiency.
Selenium. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004:194-216.