Selenium Deficiency: Signs, Causes, and Safe Ways to Improve Intake

Selenium is an essential trace mineral that rarely gets much attention, yet it plays a steady behind-the-scenes role in thyroid function, antioxidant defence, and immune health. In Europe, selenium deficiency is more common than many people realise, largely because large areas of European soil contain relatively little selenium. That means the foods grown there often provide less of this mineral than people expect. This guide explains what selenium does, who may be at higher risk of low intake, the most common selenium deficiency symptoms, and when a selenium supplement may be worth considering.

What Selenium Does in the Body

Selenium is an essential trace mineral, which means the body cannot make it and must get it from food or supplements. Although we only need it in tiny amounts, it supports several important processes throughout the body.

One of selenium’s best-known roles is in selenoproteins, a group of proteins that includes glutathione peroxidases and thioredoxin reductases. These enzymes help protect cells from oxidative stress by neutralising harmful reactive oxygen species. When selenium intake is too low, this antioxidant system may not work as well as it should.

Selenium is also important for thyroid health. The thyroid contains more selenium per gram of tissue than almost any other organ, and several selenoproteins help convert the inactive thyroid hormone T4 into the active form T3. They also help protect the gland from oxidative damage. Low selenium status has been linked with changes in thyroid metabolism, although this area is still being studied.

Beyond thyroid support, selenium contributes to immune function, supports sperm motility, and plays a role in DNA synthesis. It is a small nutrient with a wide reach.

Why Selenium Deficiency Happens in Europe

The main reason selenium deficiency is more common in Europe than in some other regions is simple geography. The selenium content of food depends heavily on the soil where crops are grown. In much of Europe, glaciation, rainfall, and soil depletion have left agricultural land relatively low in selenium. Finland addressed this decades ago by adding selenium to fertilisers as a public health measure, but most European countries have not taken the same approach.

That means even a varied diet can fall short if the food comes from selenium-poor soil. Brazil nuts are a notable exception because they are naturally very high in selenium, but most everyday foods in Europe provide only modest amounts.

Some groups are more likely to have low intake or lower selenium status:

• Vegetarian and vegan diets: Meat, fish, and eggs are reliable selenium foods, so people who avoid them need to plan more carefully.

• Gastrointestinal conditions: Conditions such as Crohn’s disease or short bowel syndrome can reduce absorption.

• Older adults: Diets may become less varied with age, which can reduce intake.

• Pregnancy and breastfeeding: Needs increase, so marginal intake can become inadequate.

• Kidney disease: People on haemodialysis may lose selenium during treatment.

Severe clinical selenium deficiency is rare in Europe, but lower-than-ideal intake is not. That matters because even when deficiency is not severe enough to cause classic deficiency diseases, it may still leave selenium-dependent systems working below their best.

Signs and Symptoms Linked with Low Selenium Status

Selenium deficiency symptoms are often vague, which is one reason low intake can go unnoticed. There is no single sign that points clearly to selenium in the way some nutrient deficiencies do. Instead, people may notice a cluster of general symptoms that could have several possible causes.

Commonly reported signs of low selenium status include:

• Persistent fatigue and general weakness
• Brain fog or difficulty concentrating
• Hair thinning or hair loss
• Brittle or slow-growing nails
• Muscle aches or weakness
• Low mood or irritability
• More frequent infections or slower recovery from illness

Because selenium supports thyroid hormone conversion, low intake can also overlap with thyroid-related symptoms such as tiredness, feeling cold, or changes in weight. But these symptoms are not specific to selenium deficiency, and they can have many other causes. A blood or serum selenium test, arranged through a GP or private clinic, is the most direct way to check status.

It is also worth keeping expectations realistic: selenium deficiency is rarely the only explanation for these symptoms. In many cases, it is one part of a broader nutritional or health picture.

Selenium Foods and Typical Intake

Good selenium foods include:

• Brazil nuts: Extremely rich, but variable. One or two nuts may provide a large amount.

• Seafood: Tuna, sardines, prawns, and oysters are all useful sources.

• Meat and poultry: Especially organ meats such as liver and kidney.

• Eggs: A practical everyday source.

• Wholegrains: Bread, pasta, and cereals can contribute, though levels vary with soil quality.

• Dairy products: Milk and yoghurt provide smaller amounts.

The EU recommended daily intake for adults is 55 micrograms per day, with slightly higher needs during pregnancy and breastfeeding. The European Food Safety Authority (EFSA) has published dietary reference values for selenium, and these reference levels reflect the fact that average intakes in several European countries are below recommended amounts.

If you eat fish a few times a week, along with eggs and some meat or dairy, you are likely getting a reasonable amount. If your diet is mostly plant-based, or you live in a region with selenium-poor soils, it is worth paying closer attention to intake.

When a Selenium Supplement May Be Worth Considering

Food should come first. For many people, small dietary changes are enough — for example, adding eggs more regularly, eating fish a couple of times a week, or including a few Brazil nuts now and then.

A selenium supplement may be reasonable if you:

• Follow a vegan or restrictive diet without reliable selenium foods
• Have a confirmed or suspected deficiency based on testing
• Have an absorption issue related to gut health
• Are pregnant or breastfeeding and struggling to meet needs through food alone

Selenium supplements usually contain either inorganic forms such as sodium selenite or selenate, or organic forms such as selenomethionine or selenium-enriched yeast. Selenomethionine is often better absorbed and retained, which is why it is commonly used in higher-quality supplements. Typical doses range from 50 to 200 micrograms per day.

If you are thinking about supplementing, check whether your multivitamin already contains selenium. It is easy to double up without meaning to.

Safety, Upper Limits, and Why More Is Not Better

This is where selenium deserves extra caution. The gap between a helpful intake and a harmful one is relatively narrow, and too much selenium can cause toxicity, known as selenosis.

EFSA sets the tolerable upper intake level for adults at 300 micrograms per day. The NHS advises that taking more than 350 micrograms per day as a supplement is likely to cause harm over time. Early signs of excess selenium can include a garlic-like breath odour, nausea, diarrhoea, fatigue, and hair loss. Some of these overlap with deficiency symptoms, which is one reason self-diagnosis can be misleading.

Brazil nuts deserve special mention. They are one of the richest selenium foods, but their selenium content varies widely. A single nut may contain anywhere from about 50 to more than 90 micrograms, depending on where it was grown. A large handful every day could push intake too high. For most people, one or two Brazil nuts a few times a week is a more sensible approach than eating them daily in large amounts.

For supplements, doses above 200 micrograms per day should only be taken under medical supervision. There is no established benefit to high-dose selenium supplementation for healthy people who already have adequate intake. In fact, large trials such as SELECT found no protective benefit from high doses and raised concerns about harm.

The takeaway is straightforward: selenium is essential, and many Europeans may not get enough, but the goal is to correct low intake safely, not to chase high doses.

Putting It Together: A Practical Approach

If you recognise some of the symptoms mentioned here, start with your diet. Do you regularly eat fish, eggs, dairy, or meat? If not, there may be room to improve selenium intake through food before reaching for a supplement.

If you have a condition that affects absorption, or if you want a clearer answer, ask your GP about a serum selenium test. Testing gives you a real data point and helps guide next steps more safely than guessing.

For most healthy adults, a varied diet that includes seafood a couple of times a week and eggs regularly will usually provide enough selenium. People following plant-based diets may need to be more deliberate and may benefit from a modest supplement or a consistent food source used sensibly.

Selenium is not a miracle mineral, and more is not better. But getting enough of it consistently matters for thyroid function, antioxidant defence, and overall wellbeing. Because selenium deficiency can be easy to miss, it is worth paying attention to without overreacting.