What Happens If You Lack Selenium? A Comprehensive Guide

December 18, 2025 •

4 min read

Worldwide, between 0.5 and 1 billion people are thought to be affected by insufficient selenium intake. Selenium is a vital trace mineral, essential for numerous bodily functions, from antioxidant defense to thyroid hormone metabolism. When levels fall below optimal, the body's systems can be significantly impacted, leading to a range of health issues.

Quick Summary

A lack of selenium, a critical trace mineral, can weaken the immune system, cause thyroid dysfunction, and impair reproductive health. Deficiency can manifest through symptoms like fatigue, hair loss, and muscle weakness. Severe cases may lead to serious conditions like Keshan disease. Addressing a selenium deficiency often involves dietary changes or supplementation to restore normal physiological function.

Key Points

Immune Compromise: A lack of selenium weakens the immune system, increasing vulnerability to infections and prolonging illness.
Thyroid Dysfunction: Selenium is critical for thyroid hormone metabolism, and its deficiency can lead to hypothyroidism symptoms like fatigue and weight gain.
Hair and Nail Health: Deficient levels can manifest as hair loss, thinning hair, and brittle or discolored nails.
Heart Health Risks: Severe, long-term deficiency is linked to conditions like Keshan disease, a form of heart failure, and exacerbated cardiovascular issues.
Cognitive Impairment: Low selenium status is associated with brain fog, confusion, and reduced cognitive function.
Reproductive Problems: Selenium plays a crucial role in fertility for both men and women, with deficiency potentially causing infertility issues.
Muscle Weakness: Chronic fatigue and muscle pain are common symptoms of inadequate selenium intake.

The Importance of Selenium for Body Functions

Selenium is a powerhouse micronutrient that is primarily integrated into proteins to form selenoproteins, which are responsible for many critical functions. These include acting as potent antioxidants to protect cells from oxidative damage, and playing a vital role in the synthesis and metabolism of thyroid hormones. A consistent and adequate supply of selenium is necessary for the proper functioning of the immune system, fertility, and heart health. A deficit can disrupt these processes, leading to noticeable and sometimes serious health consequences.

Symptoms and Health Consequences of Selenium Deficiency

The effects of low selenium levels can vary depending on the severity and duration of the deficiency. Early signs are often subtle and can easily be mistaken for other conditions. As the deficiency progresses, more distinct and severe health problems can develop.

Common Early Symptoms

Fatigue and Weakness: Selenium is involved in energy metabolism, and its deficiency can lead to feelings of persistent tiredness and overall muscle weakness.
Hair and Nail Changes: Changes in hair and nail quality are common. This can include hair loss, brittle hair, thinning hair, or white spots on the nails.
Weakened Immune Response: A lack of selenium compromises the immune system's ability to fight off infections, leading to more frequent illnesses and a slower recovery time.
Brain Fog and Cognitive Issues: Selenium's role in cognitive function means a deficit can contribute to a foggy mind, difficulty concentrating, and general cognitive decline.

More Severe Health Risks

Thyroid Dysfunction: The thyroid contains the highest concentration of selenium in the body and requires it for proper hormone synthesis. A deficiency can impair the conversion of inactive thyroid hormone (T4) to the active form (T3), leading to symptoms of hypothyroidism.
Cardiovascular Disease: Historically, severe selenium deficiency has been linked to Keshan disease, a type of congestive cardiomyopathy. It is characterized by heart failure and cardiac abnormalities, particularly impacting children and reproductive-aged women in selenium-deficient areas of China.
Reproductive Issues: Low selenium levels can negatively impact fertility in both men and women. In men, it is associated with poor sperm motility, while in women, it can affect follicle development and increase the risk of miscarriage.
Kashin-Beck Disease: This is a chronic, debilitating disorder of the bones and joints that is linked to selenium deficiency, especially during childhood. It can cause joint enlargement and restricted movement.

Factors That Increase the Risk of Deficiency

Several factors can increase an individual's susceptibility to selenium deficiency. The most prominent factor is living in a region with selenium-deficient soil, as this directly affects the selenium content of locally grown food. Other risk factors include:

Gastrointestinal Disorders: Conditions such as Crohn's disease, celiac disease, or chronic diarrhea can impair the absorption of nutrients, including selenium.
Kidney Dialysis: Patients undergoing kidney dialysis are at a higher risk of deficiency due to the loss of selenium during the treatment process.
Vegan or Vegetarian Diets: Without careful planning, plant-based diets can be lower in selenium compared to animal-based diets.
HIV Infection: Individuals with HIV have been shown to have lower selenium levels, which can further impact immune function.

Comparison of Selenium-Rich Food Sources


Food Source	Serving Size	Approximate Selenium Content	Dietary Context
Brazil Nuts	1 ounce (6-8 nuts)	544 mcg	Extremely concentrated; can easily meet and exceed daily needs.
Yellowfin Tuna	3 ounces, canned	92 mcg	Excellent source, provides a substantial portion of daily needs.
Sardines	3 ounces, canned	45 mcg	Good marine source, often including beneficial Omega-3s.
Eggs	1 large egg	15 mcg	A convenient source, widely available.
Chicken Breast	3 ounces	22 mcg	Common source of selenium in poultry.
Brown Rice	1 cup, cooked	19 mcg	Plant-based source, content can vary based on soil.
Baked Beans	1 cup	13 mcg	Provides some selenium, along with fiber.

Treatment and Prevention

Addressing a selenium deficiency typically involves increasing dietary intake of selenium-rich foods or taking supplements under medical supervision. Given that the selenium content of plant-based foods can be inconsistent due to soil variations, relying on a diverse diet or animal sources is often recommended. For severe cases, a healthcare provider may suggest supplementation, with selenomethionine being the most bioavailable form. It is crucial to monitor intake, as excessive selenium can lead to toxicity.

Conclusion

Selenium is a trace element with a profound impact on multiple physiological systems, including antioxidant defense, thyroid health, immune function, and fertility. Ignoring a deficiency can lead to a cascade of health problems, from general fatigue and hair loss to severe conditions like cardiomyopathy and joint disorders. With proper dietary awareness and medical guidance, addressing a selenium deficiency is manageable, allowing for the restoration of essential bodily functions. The key lies in recognizing the signs and taking proactive steps to ensure adequate intake of this crucial mineral.

National Institutes of Health Office of Dietary Supplements

Frequently Asked Questions

Early signs can be non-specific and subtle, such as persistent fatigue, general weakness, and a compromised immune response leading to more frequent colds. Changes to hair and nails, like thinning hair or white spots on fingernails, are also common indicators.

People with gastrointestinal disorders like Crohn's or celiac disease, those on kidney dialysis, and individuals with HIV are at an increased risk. Malabsorption issues, common in these conditions, can prevent the body from properly absorbing selenium.

Yes, inadequate selenium intake has been associated with poor mental health outcomes, including increased irritability, anxiety, and a depressed mood. These neurological and psychiatric effects are tied to selenium's role in brain function.

Selenium is vital for protecting heart cells from oxidative stress. Deficiency can worsen the effects of heart failure and lead to cardiomyopathy. Historically, severe deficiency is linked to Keshan disease, a life-threatening form of heart failure.

Diagnosis is often based on an assessment of symptoms, dietary history, and geographical location. Blood tests measuring serum selenium levels or the activity of selenium-dependent enzymes like glutathione peroxidase can help confirm a deficiency.

The most direct way is to consume selenium-rich foods. Excellent sources include Brazil nuts, seafood (tuna, sardines), poultry, eggs, and whole grains. For those with confirmed deficiency, a doctor may recommend supplements, often in the form of selenomethionine.

Supplementation can be safe and effective under medical supervision. However, because selenium can be toxic in high doses, it is crucial to consult a healthcare provider to determine the appropriate dosage and avoid negative side effects, which can include hair loss and nausea.