Dr. Thomas Dwan - Is It Bad For You? Approved by Dr. Thomas Dwan

Is Selenium Bad For You?



Short answer

Selenium is vital for health, necessary for immune function, antioxidant defense, and thyroid regulation. However, overconsumption can lead to selenosis, with symptoms like hair loss, nail brittleness, and nerve damage. Adequate intake varies: adults need 55 mcg/day, while pregnant and breastfeeding women need more. Balance is key; selenium should be obtained from diet or supplements within recommended limits to avoid deficiency or toxicity.



Long answer

Selenium: Essential Trace Mineral and Its Functions

Selenium is a micronutrient that plays an indubitable role in human health. Before we examine the potential risks associated with selenium, it's imperative to understand what selenium is and what it does in the body. Selenium is not inherently bad; like many things, it is the dose that makes the poison. Let's delineate its functions and establish why your body needs this essential trace mineral.

First and foremost, selenium is a crucial component of various selenoproteins. These selenoproteins perform vital enzymatic functions, including:

  • Antioxidant Defense: Selenium is pivotal in the antioxidant defense system, with glutathione peroxidases (GPx) being some of the key selenoenzymes. These enzymes help protect your cells from oxidative damage by neutralizing harmful free radicals, thus preserving cell integrity and function.
  • Thyroid Hormone Metabolism: Selenium-dependent enzymes are integral in the activation and deactivation of thyroid hormones. These hormones regulate metabolism, and their dysregulation can lead to health issues such as hypothyroidism or hyperthyroidism.
  • Immune System Function: Adequate selenium levels support the immune system by fostering the proliferation of immune cells and enhancing their function, which is critical in defending the body against pathogens.
  • Reproduction: Selenium is essential for normal testicular and sperm function in males, while in females, it plays a role in fertility and fetal development.

Selenium does not work in isolation. It interacts with other nutrients, such as vitamins E and C, bolstering their antioxidant activity. This kind of synergy is a testament to the complexity and interconnectedness of our body's nutritional needs.

Research has been pivotal in elucidating the importance of selenium. For example, a study published in the Journal of Nutrition & Metabolism highlighted the necessity of selenium for optimal antioxidant defenses and thyroid function, underscoring its implications for human health (Rayman, 2012). Furthermore, epidemiological studies have suggested that populations with low selenium intake may have an increased risk of certain types of diseases.

It's crucial to pinpoint that while deficiencies in selenium can lead to deleterious health outcomes, including Keshan disease—a potentially fatal form of cardiomyopathy linked to low selenium status—so too can excessive intake lead to toxic consequences such as selenosis. Therefore, it becomes a balancing act to ensure adequate intake without crossing into the territory of toxicity.

In conclusion, within this section, we recognize that selenium is an essential trace mineral that serves multiple key functions in maintaining human health. Without a shadow of a doubt, selenium is not "bad" for you; it is a necessary component of a well-rounded diet. However, we must approach its consumption with a cognizance of its potent biologic activity, adhering to recommended intake ranges to harness its benefits while avoiding adverse effects.

Selenium Deficiency vs. Adequate Intake

The human body requires a delicate balance of selenium. This trace mineral, though needed only in small amounts, plays a crucial role in the maintenance of our metabolic functions and immune system. Let's dissect the dichotomy of deficiency and adequacy to understand the potential risks and benefits.

Selenium Deficiency: Risks and Signs

Deficiency of selenium is relatively rare in most healthy individuals due to its widespread availability in a balanced diet. However, certain populations and individuals with specific health conditions might be at risk. Factors that contribute to low selenium levels include poor soil quality, living in regions where selenium is deficient in the soil, gastrointestinal disorders affecting absorption, and reliance on total parenteral nutrition.

Deficiency can lead to several health issues, and here we outline some of the most poignant:

  • Keshan Disease: A potentially fatal condition that damages the heart muscle.
  • Kashin-Beck Disease: A type of osteoarthropathy that can lead to joint pain, deformity, and short stature.
  • Myxedematous Endemic Cretinism: A form of mental retardation and physical stunting noted in certain regions.
  • Impaired Immune Response: Reduced capacity to defend against pathogens and a longer healing process for wounds.
  • Thyroid Dysfunction: Since selenium is vital for the production of active thyroid hormones, deficiency can contribute to hypothyroidism and related symptoms.

Signs of selenium deficiency can include muscle weakness, fatigue, mental fog, and frequent illness due to the weakened immune system. Selenium plays a crucial role in the activity of glutathione peroxidase, an antioxidant enzyme which defends against oxidative stress, so low levels can also have deleterious effects on overall oxidative health.

Adequate Intake: Safety and Sufficiency

For most adults, the recommended dietary allowance (RDA) for selenium is 55 micrograms per day. Meeting this selenium quota can be easily achieved by consuming selenium-rich foods like Brazil nuts, seafood, meats, and fortified foods. Supplements can be used if dietary intake is insufficient, but caution is warranted as excessive intake can lead to toxicity, also known as selenosis.

The presence of selenium within enzymes such as glutathione peroxidase and thioredoxin reductase underscores its pivotal role in various physiological processes including:

  • Antioxidant Defense: Protecting cells from damage by free radicals and reactive oxygen species.
  • Thyroid Hormone Metabolism: Facilitating the conversion of T4 to T3, the more active thyroid hormone.
  • Immune Function: Assisting in the production of prostaglandins that impact the body’s inflammatory response.

At adequate levels, selenium supports health without creeping towards the upper tolerable limit, which is set at 400 micrograms for adults. Regular blood tests can help monitor selenium status if supplementation is considered necessary. Nevertheless, the most up-to-date and precise assessments of health impact and dietary needs come from a nuanced analysis of individual health status, geographic location, and diet.

Recent studies have shed light on the necessity of maintaining this equilibrium. For instance, a study published in The Journal of Nutrition highlights that both low and high concentrations of selenium can have adverse effects on the body. The narrow safe zone that exists for selenium intake illustrates the need for careful consideration of dietary supplements and fortified foods.

In conclusion, while deficiency carries its own risks, appropriate intake of selenium is fundamental to biological function, and overshooting the mark can be just as detrimental. Knowledgeable evaluation of dietary sources and possible supplementation, when warranted, guided by professional advice, is critical in maintaining selenium adequacy without straying into potential toxicity.

The Dangers of Selenium Overdose and Toxicity

Selenium, a trace element essential for human health, must be obtained from our diet. It plays a pivotal role in the proper functioning of the thyroid gland and in protecting the body against oxidative damage. However, while selenium is indispensable, there's a razor-thin line between an adequate amount and an excess.

The risks of selenium overdose are real and serious, with a condition known as selenosis, or selenium toxicity. Unlike some nutrients where the body can handle a significant range before reaching toxic levels, selenium's therapeutic window is relatively small. The recommended dietary allowance (RDA) for adults is 55 micrograms (mcg) per day, whereas the upper intake level (UL) is set at 400 mcg per day by the National Institutes of Health (NIH).

Symptoms of Selenium Toxicity:

  • Gastrointestinal issues: Nausea, diarrhea, and abdominal pain.
  • Neurological abnormalities: Fatigue, headaches, and irritability.
  • Hair and nail brittleness and loss: Excessive intake can lead to hair falling out or nails becoming brittle or discolored.
  • Skin rash: Dermatitis is a common symptom of selenium overdose.
  • Respiratory problems: Difficulty breathing and a metallic taste in the mouth have been reported.
  • Nervous system problems: Tremors, light-headedness, and in extreme cases, neurological damage.

Scientific studies have also linked high levels of selenium to increased risk of type 2 diabetes, as mentioned in a study published in "Environmental Health Perspectives". Furthermore, the implications of elevated selenium levels on prostate health are still under examination. Initial hypotheses suggesting selenium could lower prostate cancer risk have been debunked by subsequent studies, including research from the "Journal of the National Cancer Institute," which found no protective effect against prostate cancer. In some cases, higher selenium levels have been linked to an increased risk of aggressive prostate cancer.

So, how does one typically overdose on selenium? While food sources are unlikely to cause toxicity due to naturally occurring selenium levels, the primary culprits tend to be over-supplementation and consumption of selenium-enriched products beyond recommended dosages. Problems usually arise when individuals self-prescribe supplements without professional guidance or when they consume supplements that contain selenium at concentrations significantly higher than the label claims, a not uncommon phenomenon given the lax regulatory environment surrounding dietary supplements.

Understanding Acute vs. Chronic Selenium Toxicity:

Type Onset Description
Acute Toxicity Hours to days Rapid onset of severe symptoms following a one-time ingestion of high doses of selenium (often from a supplement mishap).
Chronic Toxicity Months to years Gradual development of symptoms due to consistent overconsumption of selenium, potentially leading to more severe, long-term health complications.

In cases of suspected selenium toxicity, immediate cessation of selenium intake is recommended. Depending on the severity of the symptoms, medical intervention may be necessary. Health professionals can diagnose selenium toxicity through blood and urine tests and provide appropriate treatment to offset the effects.

As an expert in demystifying supplement myths, I urge the importance of adhering to the RDA for selenium and caution against the indiscriminate use of selenium supplements. Vitally, for those who suspect they may not be consuming enough selenium, always seek guidance from a healthcare professional to determine if supplementation is necessary and, if so, at what dosage. With supplements, more isn't always better; it's about finding the right balance.

Sources of Selenium: Natural vs. Supplemented

Selenium is an essential trace mineral crucial for many bodily processes, including cognitive function, a healthy immune system, and fertility in both men and women. It's a potent antioxidant that helps combat oxidative stress and plays a role in preventing chronic diseases. But here's where it gets tricky; the line between beneficial and excessive is perilously thin with selenium.

Natural Sources of Selenium

Selenium is naturally found in a variety of foods, with the amount varying greatly depending on the soil content where the plants were grown or where the animals were raised. Here's a list of some common food sources rich in selenium:

  • Brazil nuts (widely known as the most significant dietary source)
  • Oysters
  • Yellowfin tuna
  • Halibut
  • Sardines
  • Ham
  • Shrimp
  • Chicken and turkey
  • Eggs
  • Cottage cheese
  • Brown rice
  • Sunflower seeds
  • Baked beans

It's important to note that selenium content in food can vary greatly. For instance, a single Brazil nut can contain enough selenium to meet the daily requirement, but it can also contain enough to approach toxicity levels, especially if consuming multiple nuts daily.

Supplemented Selenium

While obtaining nutrients from natural food sources is preferable due to the synergistic balance of nutrients, some individuals might need to supplement selenium—commonly in the form of selenomethionine or sodium selenite—especially if they have health concerns that necessitate a higher intake or if their diet is insufficient.

However, because the line between a therapeutic and a toxic dose of selenium is fine, supplementation should always happen under the guidance of a healthcare professional and be tailored to individual needs. Unsupervised supplementation can lead to an excess known as selenium toxicity or selenosis, which can have serious health implications such as gastrointestinal issues, hair loss, and neurological damage.

To put this into perspective, here's a comparison of the recommended amounts versus potentially toxic levels:

Group Recommended Daily Allowance (RDA) Upper Intake Level (UL)
Adults 55 μg/day 400 μg/day
Children (4-8 years) 30 μg/day 150 μg/day
Infants 20 μg/day Not established

The RDA is established by the Institute of Medicine and varies by age and life stage. The UL is the maximum daily selenium intake unlikely to cause adverse health effects in the general population. For selenium, in particular, these thresholds are subject to debate among researchers, as individual sensitivity to selenium can vary.

Finally, when considering selenium supplements, it's essential to be aware of the form you're selecting. Some studies suggest that organic forms of selenium (e.g., selenomethionine) are potentially more bioavailable than inorganic forms (sodium selenite), but the debate among scientists and health professionals is ongoing.

Let's sum this up with a critical eye: Selenium is necessary, but it's a 'Goldilocks' nutrient where you need just the right amount. Choose whole foods as your primary source whenever possible and approach supplementation with caution, guided by informed advice and an understanding of your own dietary needs.

Balancing Selenium Intake: Recommendations for Different Populations

Selenium is a trace element essential for human health, involved in DNA synthesis, thyroid hormone metabolism, and protection from oxidative damage and infection. However, its intake needs to be carefully balanced, as both deficiency and excess can lead to health issues. Here, we breakdown the recommended intake for different population groups, taking into account the varying needs and susceptibilities.

  • Adults: The recommended dietary allowance (RDA) for adults is 55 micrograms per day. This amount is considered sufficient to meet the nutritional needs of nearly all (97-98%) healthy adults.
  • Pregnant Women: Pregnancy increases the demand for selenium. The RDA for pregnant women is elevated to 60 micrograms per day to support proper fetal growth and development.
  • Breastfeeding Women: Lactating women require an increased intake of selenium to ensure that their breast milk contains adequate selenium for the newborn. The RDA for this group is 70 micrograms per day.
  • Children: The RDA for children varies by age, with infants (up to 6 months) needing about 15 micrograms per day, and this requirement gradually increasing to 40 micrograms per day by the ages of 9-13 years old.
  • Elderly: The elderly population may need to be cautious with selenium intake due to potential interactions with medications and risk of chronic disease. While the RDA does not change, it is essential for this group to avoid excessive intake, which could exacerbate certain health conditions.
  • Individuals with Certain Medical Conditions: People with conditions such as HIV/AIDS, kidney failure, or digestive disorders may have increased selenium needs or may require monitoring to prevent toxicity. These individuals should consult a healthcare provider for personalized recommendations.

Note: It is crucial to consider dietary sources when assessing selenium intake. The primary food sources of selenium include Brazil nuts, seafood, meat, poultry, eggs, and dairy products. For individuals who follow plant-based diets or have specific dietary restrictions, attaining the RDA may require additional planning or supplementation.

It's worth mentioning that soil selenium levels vary geographically, and this can affect the selenium content of plant-based foods. Population groups in regions with low soil selenium might be at an increased risk of deficiency and should consult healthcare providers for guidance on supplements if necessary.

Dietary supplements can help in achieving the right balance but should be used judiciously to avoid overconsumption. High doses of selenium supplements, often exceeding the tolerable upper intake level (UL) of 400 micrograms per day for adults - established by the Institute of Medicine of the National Academy of Sciences - can lead to selenosis, a condition characterized by symptoms such as gastrointestinal upsets, hair loss, fatigue, irritability, and nerve damage.

When considering supplementation, it is important to look at an individual's holistic dietary pattern and to proceed with the guidance of a healthcare professional. Regular blood testing can help monitor selenium levels, ensuring they remain within a safe and optimal range. By taking a personalized approach to selenium intake, individuals can enjoy the health benefits of this vital nutrient while minimizing potential risks.

Frequently asked questions

Yes, severe symptoms of selenium deficiency such as cardiac issues indicative of Keshan disease require immediate medical attention. Similarly, signs of acute selenium toxicity, including severe gastrointestinal distress, respiratory difficulty, or neurological symptoms like tremors and extreme fatigue, necessitate urgent care. In both cases, it is crucial to seek professional medical help promptly for diagnosis and to initiate appropriate treatment.

Yes, selenium can interact with certain medications and supplements. For instance, high doses of selenium may interfere with the efficacy of cholesterol-lowering statins and anticoagulants like warfarin, potentially altering their effects. It's also important to be cautious when taking selenium with other supplements that have antioxidant properties, as they may synergistically increase antioxidant activity to potentially harmful levels. Always consult with a healthcare professional before adding selenium supplements to your regimen if you are on medication or taking other dietary supplements.

To determine if you're getting enough selenium from your diet, consider the selenium-rich foods you consume regularly, such as seafood, Brazil nuts, meats, and whole grains. If these foods are part of your diet, you're likely meeting the recommended daily intake. However, if you follow a restricted or plant-based diet, or if you live in an area with selenium-poor soil, you may be at risk of deficiency. Blood tests can accurately measure your selenium status if you suspect a deficiency or if you wish to monitor your intake.

Selenium is important for thyroid health, but individuals with thyroid issues should not automatically take extra selenium. While some studies suggest selenium supplementation may benefit those with certain thyroid conditions, such as autoimmune thyroiditis, it is not a universal recommendation. Excessive selenium intake can potentially worsen certain thyroid conditions. It is critical for individuals with thyroid issues to seek advice from a healthcare provider to determine appropriate selenium intake based on their specific condition and needs.

Ask a question about Selenium and our team will publish the answer as soon as possible.

Possible short-term side effects

  • nausea
  • diarrhea
  • abdominal pain
  • fatigue
  • headaches
  • irritability
  • skin rash
  • respiratory problems
  • nervous system problems

Possible long-term side effects

  • hair and nail loss
  • neurological damage
  • risk of type 2 diabetes
  • increased risk of aggressive prostate cancer

Commonly found in

Ingredients to be aware of

  • selenomethionine
  • sodium selenite


  • antioxidant defense
  • thyroid hormone metabolism
  • immune system function
  • reproductive health

Healthier alternatives

  • brazil nuts
  • seafood
  • meats
  • fortified foods

Thank you for your feedback!

Written by Joey Conners
Published on: 01-11-2024

Thank you for your feedback!

Written by Joey Conners
Published on: 01-11-2024

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