Selenium Toxicity

The role of selenium in health was first recognized as a toxic one by the recognition of its adverse effects. Being a trace element, only a minute amount is needed to maintain its important physiological roles.

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The recommended dietary allowance is 55 micrograms (µg) per day, based on a reference dose of 0.005 mg/kg body weight/day. The following table shows the upper levels fixed by the United States Food and Drug Administration (FDA). It is important to note that infants should not receive selenium supplementation.

Table 1: Upper Intake Levels for Selenium

Age

Male

Female

Infancy

45-60 µg

45-60 µg

1-3 years

90 µg

90 µg

4-8 years

150 µg

150 µg

9-13 years

280 µg

280 µg

14-18 years

400 µg

400 µg

Adults

400 µg

400 µg

Pregnancy and lactation

400 µg

400 µg

As of now, selenium toxicity is diagnosed based upon the presence of features of selenosis in humans, as there are no accurate biochemical or preclinical parameters.

History of selenium toxicity

Selenium toxicity in animals was detected by the occurrence of neurological and muscular symptoms in cattle during the 1930s. This was variously called alkali disease, or blind staggers, and is today thought to represent different stages of the same condition.

The clinical features of blind staggers include vision loss or impairment, random walking, poor feeding, and paralysis. In alkali disease, there is loss of hair, deformed and sloughing hooves, joint erosion, anemia, as well as cardiovascular, hepatic, and renal effects.

In animals, selenium toxicity has also been associated with abnormal fetal development in cattle, swine, and sheep, but with infertility and a higher proportion of runt offspring and fetal deaths.

Chronic selenium toxicity

The symptoms of selenium toxicity depend on the route of exposure.

Inhalation of selenium

The inhalation of selenium compounds causes respiratory membrane irritation, pulmonary edema, bronchial inflammation, and pneumonia. Elemental selenium dust exposure also produces mucous membrane irritation, bleeding from the nose, and coughing, among other symptoms.

Other features include vomiting and nausea, cardiovascular effects, headaches and malaise, and ophthalmic irritation.

Ingestion of selenium

The long-term intake of excessive selenium may involve either organic or inorganic forms in food and/or water. The symptoms of chronic selenium toxicity or selenosis first appear as a garlicky odor in the breath and a metallic taste in the mouth. This is followed by gastrointestinal symptoms such as nausea or diarrhea, tiredness, irritability, and joint pain, all of which occur in approximately 70-75% of patients.

Other characteristic features include loss of mentation, paresthesia, hyperreflexia, nail changes resulting in brittleness, deformation, and loss of nails, alopecia, discoloration and loss of teeth, as well as skin rashes. These are seen in more than 60-65% of patients.

Acute selenium toxicity

Acute toxicity presents with acute respiratory distress syndrome, myocardial infarction, renal failure, vascular symptoms such as tachycardia and flushing of the face, as well as neurological features including tremors, irritability, and myalgia. Echocardiogram (ECG) abnormalities such as T-wave inversion and QT prolongation are often seen, with death often occurring as a result of refractory hypotension

Causes of selenosis

Causes of selenosis range from ingestion of excessive selenium, as is the case of regular snacking on Brazil nuts which could contain up to 90 µg of selenium per nut. There are also many other plants that have the capability to concentrate selenium that is taken up from the soil, which are termed selenium accumulators.

In contrast to the normal plant’s selenium content of 10 parts per million (ppm), even when they grow on selenium-rich soil, selenium accumulators may have concentrations in thousands of ppm. For example, Astragalus racemosus was reported to have a concentration of almost 15,000 ppm of selenium.

These plants are able to grow only on seleniferous soils and are therefore called primary selenium indicators. While found largely in North America, some species do grow in Australia. Other selenium accumulators also exist, which can grow on selenium-poor soils and are referred to as secondary soil accumulators.

Toxic selenium compounds

The most toxic compound of selenium following inhalation is hydrogen selenide. Other toxic compounds include selenium dioxide, sodium selenite, and selenium sulfide. Sodium selenite is the most toxic compound when ingested orally.

Selenium sulfide has been linked with the occurrence of liver and lung tumors in mice and rats following oral exposure. As a result, selenium sulfide is a Group B2 carcinogen as per the Untied States Environmental Protection Agency (EPA) classification. Elemental selenium has low toxicity following oral administration.

The EPA has also classified elemental selenium as a Group D carcinogen, which indicates that it is not classifiable as a human carcinogen.

Causes of selenium toxicity

Exposure to selenium primarily occurs through food, and in some areas with seleniferous soils, through drinking water. Airborne exposure is rare; however, occupational exposure is possible with the chemical processes for recovery of selenium, painting trades, and the metal industries.

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Gun-bluing chemicals contain a high concentration of selenium and are often involved in acute poisoning. Potential sources of toxic levels of selenium include Astragalus and copper ingestion.

Toxic levels of selenium

Some agencies have put forward a chronic reference exposure level of 0.02 mg/m3 for selenium and its compounds, as well as 0.00008 mg/m3 for hydrogen selenide. These values have been determined based on findings in humans with selenosis and guinea pigs with selenium inhalation toxicity.

Interactions between selenium and other medications

Selenium may exacerbate the effects of:

  • Anticoagulants
  • Sedatives
  • Herbs that impair coagulation such as angelica, cloves, and ginger.

Selenium may impair the effects of:

  • Immunosuppressants
  • Oral contraceptives
  • Cholesterol-lowering agents
  • Niacin
  • Copper supplements

Supplements that lower the efficacy of selenium:

  • Gold salts
  • Omega-3 fatty acids
  • Zinc

References

Further Reading

Last Updated: Apr 21, 2021

Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.

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Comments

  1. Mike Ortiz Mike Ortiz United States says:

    My selenium blood level is at 196 nanograms/mililliter and I have pulmonary edima, gastrointestinal problems, damaged esophagus, hair loss, and nails are brittle. I do not know were I am getting the selenium from.

  2. Fuad Efendi Fuad Efendi Canada says:

    I think it is extremely speculative. Based on the study of five Chinese patients in 1086.

    Yes, one can die from a tablespoon of salt, and horse can die from a cigarette. Don't eat eggs: you can die if you eat more than fifty.

  3. Alex Varley Alex Varley Australia says:

    Chest rails is a known concern globally and victims of electronic harassment and gang stalking victims where they are using chemical war fare . People don't realise they are victims of these silent war crimes.....chemtrails they have found alarming statistics when analysed. How many others out there that have same symptoms?...

  4. Lisa Sims Lisa Sims United States says:

    In the past few years I've become increasingly exhausted, persistent eye infections that never really go away after several trips to the eye doctor,  left arm and leg numbness been to the chiropractor with no relief, irritability, cold intoletant feeling feverish often, soft nails frequent colds, hypothyroidism.  I can't seem to fully recovered for a period of time.  I went to my internist and had 7 blood tests done.   My selenium levels came back very high, totally out of the normal range.  I am a fitness trainer for 19 years.  I eat very healthy.  I do take vitamins, NO bodybuilding supplements. I have now stopped all vitamins.  Still feel exhausted.   I will see my internist this Thursday.  Hopefully, we can start a productive plan.  Any suggestions appreciated.

  5. Lorien G Lorien G Australia says:

    In the last section headed "Supplements which lower the efficacy of selenium" the final bullet point is "Supplements which boost the efficacy of selenium". Was this supposed to be a heading with further items below it?

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.