Selenium deficiency

Severe selenium deficiency has only been seen in those living off foods grown in selenium-deficient soil. Levels of selenium in soil vary between countries and between different regions in the same country. There are low levels in Europe, parts of the USA, New Zealand and parts of China. There are high levels in Japan, Thailand, Philippines and Puerto Rico.

Severe selenium deficiency leads to the heart disorder, Keshan disease, a potentially fatal cardiomyopathy that affects children in low selenium areas of rural China. Kashin Beck disease, another deficiency disease seen in rural China, resembles arthritis.

Selenium deficiencyMarginal selenium deficiency can occur in alcoholics and those living on refined and processed foods, and may increase the risk of a variety of diseases. Blood selenium levels may also be low in those who are critically ill, AIDS patients, fibrocystic breast disease sufferers, those with Down syndrome, and liver disease patients.

Cancer

Epidemiological studies have shown that those who live in areas of low selenium soil are more prone to cancer than those living in areas where the soil is high in selenium. Blood samples taken from large groups of people show that they are more likely to develop cancer if they have low blood levels of selenium and glutathione peroxidase. Low serum, dietary and soil selenium levels are particularly associated with lung and gastrointestinal tract cancers.

Colorectal cancer

In a 1997 study of the relationship between selenium and colon cancer, researchers at the University of North Carolina determined selenium levels in patients referred for colonoscopy. The results showed that those with the lowest selenium levels had almost four times the risk of colon cancer when compared to those with the highest levels.

A 1998 German study assessed the selenium and glutathione peroxidase levels in 106 colorectal cancer patients and compared these to a gender-matched and age-matched control group. When average selenium levels in the cancer patients were compared with those in the control group, no significant differences were found. However, a significant reduction of serum glutathione peroxidase activity was seen in cancer patients. Those patients with low selenium levels had lower survival times and rates than the patients with higher selenium levels. The lowest selenium level was found for patients with advanced tumor disease.

It is unclear from the results of this study whether low selenium levels are a cause or effect of cancer.

Lung cancer

I n a study that started in 1986 and was published in 1993, Dutch researchers examined the links between longterm selenium status and lung cancer among 120,852 Dutch men and women aged 55-69 years. The results showed that the lung cancer risk in those with the highest intake of selenium was half that of those in the lowest intake group. The protective effect of selenium was concentrated in subjects with a relatively low dietary intake of beta carotene or vitamin C.

Cardiovascular disease

Severe selenium deficiency leads to weakened and damaged heart muscle. People living in low selenium areas have lower plasma selenium levels and an increase in the risk of coronary disease, atherosclerosis, platelet aggregation and levels of compounds such as prostaglandins and leukotrienes which play a role in inflammation and platelet aggregation. Selenium seems to be able to affect prostaglandin and leukotriene synthesis.

Selenium deficiencyAs part of glutathione peroxidase, selenium takes part in the reduction of hydrogen peroxides and lipid peroxides. The concentration of these peroxides, in turn, affects platelet aggregation. Blood platelets of selenium-deficient people show increased aggregation, which selenium administration inhibits. Thus longterm supplementation with low doses of selenium could have a beneficial effect on the prevention of both thrombosis and coronary heart disease in people who are selenium-deficient.

Dutch researchers studying the association between selenium status and the risk of heart attack, compared plasma, red blood cell, and toenail selenium levels and the activity of red blood cell glutathione peroxidase among 84 heart attack patients and 84 healthy people. They found lower selenium levels in all the heart attack patients. Because the toenail selenium level reflects blood levels up to one year before sampling, the results suggest that low selenium levels were present before the heart attacks and, may have played a role in causing them.

However, results from the Physicians' Health Study published in 1995 do not suggest a link between selenium levels and heart attack risk. Researchers analyzed blood selenium levels in 251 subjects who had heart attacks and an equal number of healthy people, matched by age and smoking status. The results did not show significant differences.

HIV/AIDS

As part of the antioxidant enzyme glutathione peroxidase, selenium is necessary to help prevent oxidative damage and to help the immune system function effectively. Levels of this enzyme have been shown to be low in some HIV- positive patients, particularly in those with more advanced stage of the disease, and low selenium levels appear to be associated with low CD4+ lymphocyte counts and with higher death rates in AIDS patients. Deaths from AIDS are higher in areas where soil selenium is low.

Birth defects

Selenium deficiency in women may result in infertility, miscarriages, neural tube defects and retention of the placenta.

Asthma

As an antioxidant, selenium may be able to protect against the damage to lung tissue and enzymes caused by the free radicals produced by inflammatory cells in asthmatic airways. As a component of the enzyme glutathione peroxidase it helps to stabilize cell membranes.

In a New Zealand study done in 1994, researchers examined 708 children for symptoms of wheezing. They then measured selenium levels in blood sam- ples taken eight years previously from 26 of the children with current wheezing, and compared these with levels in 61 healthy children. The results showed that wheezing was more common in those with low levels of selenium. Another New Zealand study, done in 1990, showed that whole blood selenium concen- trations and glutathione peroxidase activity were lower in adults with asthma than in those without.

Rheumatoid arthritis

Free oxygen radicals are involved in the inflammatory process seen in rheumatoid arthritis and are generated mainly by white blood cells. Selenium is important to the functioning of the immune system and to the inflammatory process. Low selenium levels among patients with rheumatoid arthritis have been reported from areas with both high and low natural selenium intake. The reduction seems to be related to the clinical disease activity in arthritis patients, and selenium concentrations have been found to fluctuate during the disease.

Cataracts

Reduced antioxidant defenses seem to play a role in cataract formation and selenium deficiency may play a part in this. Glutathione peroxidase is found in

high concentrations in the lens and selenium levels in lenses with cataracts have been found to be lower than in normal lenses.

Anemia

Selenium deficiency may play a role in causing or aggravating anemia as glutathione peroxidase protects red blood cells from free radical damage and destruction.

Other effects

A 1996 study done at the USDA Human Nutrition Research Center in San Francisco suggests that people with low selenium levels might experience depressed moods, supporting the idea that selenium plays a special role in the brain. However, the study did not find improvements with selenium supplementation in people eating a typical American diet.

 
 
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