Selenium is a trace mineral, but its impact on human health is anything but small. It plays a critical role in thyroid function, immune defence, fertility, and the body’s antioxidant systems. In the UK, mild selenium deficiency is more common than many people realise, largely due to lower selenium levels in European soils. Understanding why selenium matters — and how to get enough — is key to long-term health.
Selenium’s Role in Thyroid Enzymes
The thyroid gland contains more selenium per gram of tissue than any other organ in the body. This is because selenium is essential for iodothyronine deiodinase enzymes, which convert the inactive thyroid hormone T4 into the active form T3.
Without adequate selenium:
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Thyroid hormone activation becomes inefficient
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Metabolism, energy levels, and temperature regulation may suffer
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The thyroid becomes more vulnerable to oxidative stress
Selenium also supports enzymes such as glutathione peroxidase, which protect thyroid tissue from damage during hormone production — a process that naturally generates free radicals.
Natural Sources of Selenium
Selenium is best obtained from whole foods, with just small amounts required daily.
Key dietary sources include:
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Brazil nuts – one of the richest natural sources (only 1–2 nuts can meet daily needs)
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Eggs – a convenient, bioavailable source
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Tuna and other seafood – particularly beneficial for those who eat fish regularly
Other contributors include whole grains, seeds, and poultry, though selenium content varies depending on soil quality.
Health Benefits of Selenium
Adequate selenium intake supports several essential body systems:
Fertility & Reproductive Health
Selenium is vital for sperm motility and quality in men and supports healthy egg development in women.
Immune Function
It helps regulate immune responses and supports the body’s ability to fight infections and recover from illness.
Antioxidant Defence & Detox Support
Selenium is a key component of antioxidant enzymes that neutralise free radicals, supporting liver detox pathways and reducing cellular damage linked to ageing and chronic disease.
Signs and Consequences of Selenium Deficiency
Long-term low selenium intake may contribute to:
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Thyroid imbalance or worsening autoimmune thyroid conditions
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Fatigue and low energy
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Weakened immunity and increased infection risk
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Reduced fertility
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Higher oxidative stress and inflammation
In the UK, selenium intake has declined over the past few decades, making mindful dietary choices increasingly important.
Supporting Selenium Intake Naturally
Because selenium requirements are small, balance is crucial. Excess intake — particularly from supplements — can be harmful. For most people, focusing on food sources is the safest and most effective approach.
Selenium is a quiet but powerful mineral, essential for thyroid health, immune resilience, fertility, and antioxidant protection. Ensuring a steady intake from quality food sources can help support energy levels, hormone balance, and long-term wellbeing.
Support your thyroid and antioxidant defences naturally by choosing nutrient-dense foods rich in selenium as part of a balanced, whole-food diet — small nutrients can make a big difference.