Written by Charles Gumbley, BHSc (Clinical Nutrition), DipHSc (Western Herbal Medicine)
Evidence checked: 20 July 2026
This article provides general nutrition education, not a diagnosis or personal supplement dose. Selenium has a relatively narrow range between nutritional need and excess. Speak with a doctor, pharmacist or Accredited Practising Dietitian before supplementing during pregnancy, for thyroid or fertility concerns, or if you have kidney disease, cancer treatment or unexplained symptoms.
Conflict disclosure: Nutrition Market sells supplements. No product is ranked or linked. Any future commercial placement must pass exact label, ARTG, dose, stock, COGS, margin and clinical-placement checks.
Selenium is an essential mineral and trace mineral incorporated into selenoproteins. These proteins include glutathione peroxidases, thioredoxin reductases and iodothyronine deiodinases involved in redox control, thyroid-hormone metabolism and normal cell function.
The established value of selenium comes from meeting nutritional requirements and correcting low status. This does not show that extra selenium burns fat, prevents cancer, reverses thyroid disease, improves cognition or increases fertility in someone whose intake is already adequate.
Key points
- Australian RDIs are 70 micrograms per day for adult men and 60 micrograms for adult women.
- Seafood, poultry, eggs and meat are reliable dietary sources; grain content varies with soil and origin.
- Brazil nuts can contain very high and highly variable amounts, so they are not a precision supplement.
- Low status is uncommon in Australia but can occur with severe restriction, malabsorption or long-term parenteral nutrition without adequate selenium.
- The Australian adult upper level is 400 micrograms per day from food and supplements combined.
- Too much can cause garlic-like breath, metallic taste, nausea, hair loss, brittle nails, rash, fatigue and neurological symptoms.
Selenium in the Body: Thyroid and Antioxidant Selenoproteins
Selenium is an essential component of at least 25 human selenoproteins. Glutathione peroxidases help manage peroxides produced during metabolism, while thioredoxin reductases support cellular redox systems. These antioxidant functions do not mean that high-dose selenium supplements provide general “detox” protection.
Iodothyronine deiodinases help convert thyroxine, or T4, to active triiodothyronine, or T3, and also inactivate thyroid hormones. Adequate status therefore supports normal thyroid metabolism. Taking selenium is not a substitute for thyroid testing, levothyroxine or investigation of autoimmune thyroid disease. Trials in Hashimoto’s thyroiditis have reported changes in some antibody markers, but evidence has not established consistent symptom, quality-of-life or disease-course benefits.
Other selenoproteins have roles in DNA synthesis, reproduction and immune function. The role of selenium in these pathways is not the same as a treatment effect, particularly once selenium-dependent enzymes are already adequately supplied. Low and high selenium exposure can both be undesirable.
Best Sources of Selenium and Australian Selenium Intake
The best sources of selenium depend partly on where food was grown or raised. In Australia and New Zealand, seafood, poultry and eggs are major dietary sources of selenium, with meat contributing as well. The selenium content of the soil affects plant foods and grain. Fish, shellfish, chicken, turkey, beef, pork, eggs, dairy, whole grains, legumes, seeds and some nuts can contribute.
Brazil nuts are frequently described as the food highest in selenium. Their content varies dramatically between nuts and growing regions. One nut may provide a substantial share of the daily requirement, while several high-content nuts could approach or exceed the upper level. Eating them by count is not a reliable way to deliver a prescribed dose.
Australian adult RDIs are 70 micrograms daily for men and 60 micrograms for women. The RDI is 65 micrograms in pregnancy and 75 micrograms during lactation. These are population intake values, not treatment doses. Food variety is safer than repeatedly relying on one unusually concentrated food.
Selenium Deficiency Signs, Risk and Testing
What are the signs of selenium deficiency? Mild low status may have no specific symptoms. Severe inadequacy can contribute to muscle weakness or pain, cardiomyopathy, altered thyroid metabolism, immune changes and fertility problems, but these findings have many other causes.
Keshan disease is an endemic cardiomyopathy described in very low-selenium areas of China. Low intake was necessary but probably not sufficient; viral and environmental factors also contributed. Kashin-Beck disease is an osteoarthropathy found in some deficient regions, but selenium replacement alone has not been shown to explain or correct every case.
Risk can rise with severe malnutrition, malabsorption, bariatric surgery, dialysis and long-term parenteral nutrition without adequate provision. Soil selenium patterns matter geographically. Plasma or serum selenium can reflect recent intake, while blood selenium levels and hair and nail measurements have different limitations. Results require clinical and dietary interpretation rather than a supplement trial based on symptoms alone.
Health Benefits of Selenium: Cancer, Cognition, Thyroid and Fertility
Observational studies can associate low selenium levels with worse outcomes, but illness can lower status and confounding is substantial. Supplement trials are more useful for deciding whether additional selenium changes health outcomes.
Large randomised cancer-prevention trials did not show that routine selenium supplementation prevents prostate cancer in generally well-nourished men. SELECT used 200 micrograms of selenium per day. Some analyses raised concern about type 2 diabetes or high-grade prostate cancer in particular baseline-status groups, while an earlier trial reported more non-melanoma skin cancer in supplemented participants. Selenium should not be used as cancer prevention or alongside cancer treatment without oncology advice.
Research has not established supplementation as a treatment for dementia, asthma or cardiovascular disease. Correcting true deficiency is different from adding selenium above adequate intake.
For fertility, selenoproteins participate in sperm structure and antioxidant systems. Low status may coexist with infertility, but trials do not support a universal selenium dose for male or female fertility. What does selenium do in a woman’s body? It supports the same thyroid, antioxidant and cellular functions as in men; requirements rise modestly in pregnancy and lactation. It does not regulate weight, guarantee conception or replace prenatal care.
Selenium Supplements and Excessive Selenium Intake
Selenium supplements may contain different forms of selenium: selenomethionine, selenium-enriched yeast, sodium selenite or sodium selenate. Absorption and tissue handling differ, and a higher amount is not automatically better. Anyone planning to take a selenium supplement should check multivitamins, thyroid blends, fertility products and stand-alone products before combining diet and products.
The Australian adult UL is 400 micrograms per day from all sources combined. It is a ceiling, not a target. Some authorities have adopted lower contemporary limits, adding another reason to avoid unsupervised high-dose use.
Chronically high intakes could lead to selenium toxicity, or selenosis. Signs include garlic-like breath, metallic taste, nausea, diarrhoea, fatigue, irritability, rash, hair loss and brittle or lost nails. Acute poisoning can affect the nervous system, kidneys, heart and lungs. Stop the suspected product and contact a healthcare professional or the Poisons Information Centre on 13 11 26 if overdose is possible.
Questions About Selenium
What are the signs of selenium deficiency?
There may be no specific early sign. Severe deficiency can contribute to muscle weakness, cardiomyopathy, altered thyroid metabolism, immune changes and fertility problems. These features require assessment because many other conditions cause them.
What food is highest in selenium?
Brazil nuts are often highest, but the amount varies so widely that they are not a dependable dose. Seafood, poultry, eggs, meat and some grains are steadier food sources.
What does selenium do in a woman’s body?
It supports selenoproteins involved in thyroid-hormone metabolism, antioxidant systems, reproduction and cell function. Australian intake needs are 60 micrograms daily for adult women, 65 in pregnancy and 75 during lactation. More is not necessarily better.
Does selenium burn belly fat?
No good clinical evidence shows that selenium burns belly fat. Correcting deficiency may restore normal physiology, but a supplement does not selectively reduce abdominal fat. Sustainable dietary, activity, sleep and medical approaches matter more.
References
- National Health and Medical Research Council. Australian nutrient reference values: selenium. Accessed 20 July 2026.
- National Institutes of Health Office of Dietary Supplements. Selenium: fact sheet for health professionals. Accessed 20 July 2026.
- Lippman SM, et al. Effect of selenium and vitamin E on risk of prostate cancer: SELECT. JAMA. 2009;301(1):39–51. doi:10.1001/jama.2008.864.
Charles Gumbley founded Nutrition Market to make evidence-informed supplement guidance more accessible. He writes about supplement evidence and product selection for Nutrition Market. Site content is educational and not individual clinical advice.
