Originally written by ZRT Laboratory author. Reproduced with permission. Last reviewed: May 2026.
As the human population grows and global connectivity increases, the emergence and spread of new viral infections has become an increasingly frequent reality. While the world looks to vaccines and pharmaceutical interventions, one of the most overlooked defences against viral disease may be something far more fundamental: adequate selenium nutrition.
This article explains the science behind selenium’s role in immune defence and viral protection, the geographical link between selenium-deficient soils and emerging infectious diseases, the impact of heavy metal exposure on selenium status, and how to confirm whether your selenium levels are adequate.
What Is Selenium and Why Does the Immune System Need It?
Selenium is an essential trace element with a wide range of critical biological functions. It is incorporated into a family of proteins called selenoproteins — of which at least 25 are known in the human body — by replacing a sulphur atom in the amino acid cysteine to form selenocysteine. The majority of selenoproteins exhibit antioxidant properties, with glutathione peroxidase (GPx) being among the most important.
Selenium’s roles in the body include:
- Antioxidant defence — GPx and other selenoproteins neutralise reactive oxygen species (ROS), protecting cells from oxidative damage
- Immune regulation — selenium supports both innate and adaptive immune responses, including the activity of natural killer cells and T lymphocytes
- Thyroid hormone metabolism — the deiodinase enzymes that convert inactive T4 to active T3 are selenoproteins
- Anti-inflammatory activity — selenium modulates inflammatory signalling pathways
- DNA repair and protection — selenoproteins support genomic stability and reduce mutation rates
How Selenium Protects Against Viral Infections and Mutations
When a virus infects a host cell, it generates reactive oxygen species as a by-product of replication. These ROS cause oxidative stress within the cell, which — if not adequately neutralised — accelerates viral replication and increases the rate of viral mutation. Viral mutations are the mechanism by which new, potentially more virulent or vaccine-resistant strains emerge.
Selenium-dependent GPx and other antioxidant selenoproteins directly combat this viral oxidative stress, slowing replication and reducing the likelihood of mutation. In selenium-deficient hosts, this antioxidant defence is impaired — creating conditions that favour faster viral replication, more severe infection, and a higher probability of viral evolution into new strains.
Animal studies have demonstrated this relationship clearly. Research using mice showed that selenium deficiency significantly increased the pathology and duration of influenza virus infection, and that low selenium intake resulted in markedly decreased GPx activity. A benign human enterovirus was shown to become virulent in selenium-deficient mice — demonstrating that the nutritional status of the host can directly influence the pathogenicity of a virus.
The chain of causation is straightforward: selenium deficiency → reduced antioxidant defence → increased viral oxidative stress → accelerated viral replication and mutation → emergence of new viral strains.
Our Heavy Metals & Mineral Balance Test measures selenium alongside a comprehensive panel of essential minerals and toxic heavy metals using ICP-MS analysis on both blood spot and dried urine samples — the gold standard methodology for trace element assessment.
Selenium-Deficient Soils and the Geography of Emerging Viruses
A landmark 2011 publication in Biological Trace Element Research drew a striking geographical connection between selenium-deficient soils and the origin of major viral infectious diseases — including HIV/AIDS, influenza, SARS, Ebola, swine flu, and bird flu. Mapping areas of soil selenium deficiency against the geographic origins of these viral outbreaks revealed a consistent overlap.
Countries such as China, where selenium-deficient soil is widespread across large agricultural regions and urban populations number in the tens of millions, are particularly susceptible to viral evolution and spread. When populations subsisting on locally grown food are chronically selenium-deficient, the conditions for viral mutation and emergence are significantly enhanced.
This does not mean that selenium deficiency is the sole cause of viral emergence — but it represents a modifiable nutritional risk factor that is frequently overlooked in public health discussions about infectious disease prevention.
Heavy Metal Exposure and Selenium Depletion
Selenium status can be further compromised by exposure to certain heavy metals — particularly mercury and arsenic — which have a high chemical affinity for selenium. When mercury or arsenic binds to selenium in the body, it renders the selenium biologically unavailable, effectively depleting the selenium pool needed for selenoprotein synthesis and antioxidant defence.
The most significant sources of mercury and arsenic exposure include:
- Mercury: coal-fired power plants (atmospheric deposition into water and soil), large predatory seafood (tuna, swordfish, shark), dental amalgam fillings, and certain industrial occupations
- Arsenic: contaminated well water (a major issue in parts of South Asia, South America, and rural areas globally), rice and rice-based products, certain pesticides, and industrial pollution
In areas with elevated environmental or industrial heavy metal levels, maintaining selenium sufficiency becomes even more critical — and more difficult. Testing both selenium and heavy metals simultaneously provides the most clinically meaningful picture of element status and its implications for immune health.
Our Thyroid, Heavy Metals & Essential Elements Test measures selenium, mercury, arsenic, and other key elements alongside thyroid markers — providing a comprehensive assessment of how your element status is affecting thyroid function and immune health in a single at-home collection.
Other Essential Elements for Immune Health
Selenium is not the only micronutrient with a critical role in immune defence. Several other essential elements work alongside selenium to support optimal immune function:
- Zinc — essential for the development and function of immune cells, wound healing, and antiviral defence. Zinc deficiency is one of the most common micronutrient deficiencies globally and significantly impairs immune response.
- Copper — supports the activity of immune cells and has direct antimicrobial properties. Copper surfaces have been shown to inactivate viruses and bacteria.
- Iodine — essential for thyroid hormone production, which regulates immune function and metabolic rate. Iodine deficiency impairs thyroid-mediated immune regulation.
- Iron — required for the proliferation and maturation of immune cells. Both deficiency and excess impair immune function.
Because these elements interact with one another and with selenium, assessing them together provides a more complete picture of immune nutritional status than testing any single element in isolation.
How to Ensure Adequate Selenium Status
Dietary selenium intake varies enormously depending on the selenium content of local soils and the foods consumed. In the UK, selenium intake has declined significantly over recent decades following a shift from North American wheat (grown in selenium-rich soil) to European wheat (grown in selenium-poor soil) in bread production. UK adults are among the most selenium-deficient populations in the developed world.
Dietary sources of selenium include Brazil nuts (highly variable in content), seafood, meat, eggs, and dairy. Selenium supplements are widely available, but because both deficiency and excess carry health risks, supplementation without testing is not recommended. The tolerable upper intake level for selenium is 400 µg per day; toxicity (selenosis) can occur above this level with chronic supplementation.
Because approximately 50–70% of absorbed selenium is excreted in urine, urinary selenium concentration provides a reliable indicator of daily intake. Blood selenium reflects longer-term status. Testing both sample types — as offered by ICP-MS analysis — provides the most complete picture of selenium status across different body compartments.
Our Iodine & Creatinine Dried Urine Test Kit can be used alongside selenium testing to assess the status of both key thyroid and immune-supporting elements simultaneously, using a simple at-home dried urine collection analysed by ICP-MS.
Frequently Asked Questions
How does selenium protect against viral infections?
Selenium-dependent antioxidant enzymes — particularly glutathione peroxidase — neutralise the reactive oxygen species generated during viral replication. By reducing oxidative stress within infected cells, selenium slows viral replication and reduces the rate of viral mutation. In selenium-deficient individuals, this antioxidant defence is impaired, leading to more severe infections and a higher likelihood of viral evolution into new strains.
What are the symptoms of selenium deficiency?
Symptoms of selenium deficiency include fatigue, muscle weakness, hair loss, brittle nails, impaired immune function, thyroid dysfunction (particularly impaired T4 to T3 conversion), and increased susceptibility to infection. Severe deficiency is associated with Keshan disease (a cardiomyopathy) and Kashin-Beck disease (a musculoskeletal disorder), both of which occur in severely selenium-deficient regions of China.
Can you get too much selenium?
Yes. Selenium toxicity (selenosis) can occur with chronic intake above 400 µg per day. Symptoms include hair loss, brittle nails, garlic breath odour, nausea, fatigue, and in severe cases, neurological damage and organ failure. Because the margin between adequate and toxic selenium intake is relatively narrow, testing before supplementing is strongly recommended.
How does mercury affect selenium levels?
Mercury has a very high chemical affinity for selenium and binds to it in the body, forming mercury-selenium complexes that are biologically inert. This effectively sequesters selenium, reducing the amount available for selenoprotein synthesis and antioxidant defence. Regular consumption of high-mercury seafood (tuna, swordfish, shark) or significant mercury exposure from other sources can meaningfully deplete selenium status over time.
Why is selenium deficiency common in the UK?
UK soils are naturally low in selenium, and the shift from importing North American wheat (grown in selenium-rich prairie soils) to using European wheat (grown in selenium-poor soils) in bread production has significantly reduced dietary selenium intake in the UK over recent decades. UK adults have among the lowest selenium intakes in the developed world, making testing and appropriate supplementation particularly relevant for the UK population.
What is the best way to test selenium levels?
Testing both urinary and blood selenium provides the most complete picture. Urinary selenium reflects recent dietary intake (as 50–70% of absorbed selenium is excreted in urine), while blood selenium reflects longer-term status. ICP-MS analysis — the gold standard in trace element measurement — provides the accuracy and sensitivity needed for reliable clinical assessment of selenium and other essential and toxic elements.
References
[1] Sanjuán R, Domingo-Calap P. Mechanisms of viral mutation. Cell Mol Life Sci. 2016;73:4433–4448.
[2] Guillin OM, et al. Selenium, selenoproteins and viral infection. Nutrients. 2019;11:2101.
[3] Beck MA, et al. Selenium deficiency increases the pathology of an influenza virus infection. FASEB J. 2001;15:1481–3.
[4] Beck MA, et al. Benign human enterovirus becomes virulent in selenium-deficient mice. J Med Virol. 1994;43:166–70.
[5] Harthill M. Review: micronutrient selenium deficiency influences evolution of some viral infectious diseases. Biol Trace Elem Res. 2011;143:1325–1336.
Originally written by ZRT Laboratory author. Reproduced with permission. Last reviewed: May 2026.