First discovered in 1817 by Swedish chemist Jöns Jacob Berzelius, selenium is a mineral named after Selene, the Greek goddess of the moon. It’s found in living organisms, including soil and plants. But within the context of human nutrition, only a small amount is needed to help support optimal health, which is why it’s considered a “trace mineral.”1
According to published research, without enough selenium, your body struggles to fight off infections, regulate hormones, and combat oxidative stress that leads to chronic disease. Fortunately, there are many dietary sources of this mineral, and supplementation is also readily available.
Selenium’s Role in Protecting Your Cells and Preventing Disease
In a study published in Metal Ions in Life Sciences,2 researchers examined the varied yet important roles of selenium in human health, particularly through its incorporation into specialized proteins called selenoproteins. Essentially, selenoproteins are proteins synthesized from the 21st amino acid, selenocysteine.
• The protective role of selenoproteins — They help drive critical antioxidant defenses, protect against cell damage, and support metabolic functions. Researchers explored how selenium deficiency leads to serious health conditions, while optimal selenium intake enhances cellular function and longevity.
• Selenium affects various organ systems — These include your immune system, brain, thyroid, and cardiovascular health. It highlighted how selenium-containing proteins, especially glutathione peroxidase and thioredoxin reductase, are required for neutralizing harmful oxidative stress in the body.
Without these defenses, cells face accelerated aging and damage, increasing your risk of chronic diseases like heart disease, neurodegenerative disorders, and metabolic dysfunctions.3
• Small but essential — Selenium is a trace mineral, but its impact is felt throughout your entire body. The study found that its selenoproteins influence everything from immune response to DNA repair. These proteins act as the body’s built-in defense system against oxidative damage. Left unchecked, this damage contributes to everything from cancer to diabetes.4
• Selenium supports antioxidant synthesis — One of the most essential functions of selenium is its role in supporting glutathione peroxidase, a powerhouse antioxidant enzyme. The study also found that individuals with lower selenium levels exhibited reduced activity of this enzyme, leaving their cells more vulnerable to oxidative stress and related diseases.5
Selenium’s Role in Other Important Biological Processes
The study also sheds light on selenium’s impact on cardiovascular health and other systems that sustain life.
• Selenium deficiency affects cardiovascular health — Regions with selenium-deficient soil, like parts of China, historically had high rates of Keshan disease — a fatal heart condition caused by selenium deficiency. The study highlighted how selenium supplementation in these areas led to a sharp decline in Keshan disease rates, showcasing the importance of this mineral for heart function.6
• The benefits extend to the brain — The study found that neurons require selenium-dependent proteins to function properly and protect against neurodegeneration. This is especially important for elderly people, as oxidative stress plays a central role in conditions like Alzheimer’s and Parkinson’s disease.
Researchers observed that selenium-deficient animals developed neurological dysfunction, reinforcing the hypothesis that selenium is required for long-term cognitive health.7
• Influence in hormone activation — A noteworthy finding from the study was selenium’s involvement in thyroid function. For context, the thyroid gland produces hormones that regulate metabolism, but these hormones need to be activated in the right way for the body to use them.
Selenium is required for enzymes that convert the inactive thyroid hormone (T4) into its active form (T3). Without enough selenium, this process is disrupted, leading to symptoms like fatigue, weight gain, and sluggish metabolism.8
Individuals with thyroid disorders, particularly Hashimoto’s thyroiditis, were found to have lower selenium levels, which contribute to increased inflammation in the thyroid gland. The research pointed out that optimizing selenium intake helped improve thyroid hormone conversion and reduced markers of inflammation in these individuals, showing that selenium supplementation is a useful tool in thyroid disease management.9
• Selenium supplementation improves immune function — Selenium also supports white blood cell activity, helping your body mount stronger defenses against infections. Individuals with low selenium levels were more likely to suffer from chronic infections and slower wound healing.10
Selenium Also Helps Fight Cancer
In addition to all the benefits discussed above, selenium has also been found to have anticancer potential, according to Aliasger Salem, Ph.D., associate vice president for research at the University of Iowa College of Pharmacy.11
• The chemopreventative capabilities of selenium — Interestingly, scientists originally believed that selenium was a carcinogen. However, a study cited by Salem, published in the 1960s, challenged this notion12 and proposed that it helps fight cancer.
• Modern research supports these findings — A 2022 study confirmed that selenium is “a chemopreventative agent with variable results depending on the type and dose of selenium used.” Specifically, it helps normalize tumor vasculature, which helps increase cancer-fighting treatments to tumor cells.
Selenium also has the ability to create an optimal window to administer anticancer therapeutics, which help improve the outcomes of patients receiving treatment.13
• Mechanism behind selenium’s anticancer properties — According to Salem’s own experiments, selenium compounds such as methylselininc acid (MSA) and seleno-L-methionine (SLM) have been shown to target proteins that cause tumor growth and drug resistance.
Salem shares, “Studies from my team and I have found that MSA can modulate key biochemical pathways related to kidney cancer by reducing levels of proteins that influence tumor growth and immune evasion. We also observed that SLM may slow kidney tumor growth in mice without toxic side effects.”14
In another study conducted by Salem, he noted that combining SLM with a chemotherapy drug effectively treated metastatic kidney cancer while causing minimal side effects. Of the 27 patients he treated, more than half of them had their tumors shrink in size, supporting the hypothesis that selenium boosts the effectiveness of anticancer therapies.15
How to Optimize Your Selenium Intake
Based on the published research, getting sufficient amounts of selenium will help support your cellular health and lower your risk of cancer, as well as protect your brain and thyroid functions. I recommend you get your selenium from natural sources. This will help avoid adverse effects associated with excessive doses. Here are my recommendations:
1. Eat more selenium-rich foods — Your first line of defense against disease (as well as a pillar for optimal health) is your diet. Selenium is found in high concentrations in certain animal and plant foods. Some of the best sources include eggs, grass fed meats like beef and lamb, and fatty fish such as sardines (make sure fish are wild-caught and not farmed).
Dairy products also contain selenium, but make sure they are made from raw, grass fed milk. This is the superior choice compared to conventionally made milk because the pasteurization process destroys beneficial compounds.
If your soil is naturally low in selenium (common in parts of Europe, China, and New Zealand), food alone may not be enough. In this case, I recommend taking a selenium supplement.
2. Reminders when considering supplementation — Selenium supplements are widely available, but a higher dose isn’t always better. If you’re already getting enough from your diet, excess selenium will lead to toxicity.
According to Salem, taking in too much selenium will cause selenosis, “a condition with symptoms such as brittle hair and nails, digestive issues, skin rashes and neurological symptoms such as irritability and fatigue. In severe cases, selenium toxicity can result in organ failure and death.”16 That said, here are the recommended guidelines when taking a selenium supplement:
• Be mindful of your total daily intake — The recommended daily allowance for selenium ranges from 15 micrograms (mcg) for infants to 55 mcg for men and women over 19 years.
• Use the right form — Selenomethionine has a high bioavailability. Other types of selenium supplements include selenium-enriched yeast, selenite and selenate.17 Whichever you choose, make sure to do your due diligence and purchase a high-quality product.
• Avoid synthetic blends — Some supplements contain cheap fillers or poorly absorbed forms of selenium.
3. Avoid foods that deplete selenium — Just as certain foods boost selenium, others deplete it or make it harder for your body to absorb. Ultraprocessed foods, which are high in unhealthy ingredients like linoleic acid, eventually cause selenium deficiency.18 The biggest culprits include:
• Vegetable oils — Stay away from soybean, corn, and sunflower oils, which increase inflammation and oxidative damage.
• Refined sugar and artificial sweeteners — Products containing artificial sweeteners and high-fructose corn syrup contribute to gut issues that interfere with nutrient absorption.
• Factory farmed meats — These animals are often deficient in selenium.
4. Support your thyroid — Selenium is key for optimal thyroid function, but it doesn’t work alone. To round things out, pairing selenium with other supportive nutrients helps your thyroid synthesize hormones properly. Make sure you’re getting enough:
• Magnesium — Required for overall metabolic health and works alongside selenium for enzyme function.
• Iodine (in moderation) — Too much iodine worsens thyroid issues, so keep intake below 200 mcg per day.
• Vitamin D — This hormone regulates immune function and prevents inflammation that disrupts thyroid activity. For in-depth instructions on how to optimize your vitamin D levels, read my article “Vitamin D Deficiency Complicates Autoimmune Diseases.”
Frequently Asked Questions About the Role of Selenium for Optimal Health
Q: Why is selenium important for the body?
A: Selenium is a trace mineral essential for numerous bodily functions, including immune support, antioxidant protection, and thyroid hormone regulation. It plays a key role in preventing oxidative stress, reducing inflammation, and protecting against chronic diseases such as heart disease, neurodegenerative disorders, and cancer.
Q: How does selenium help fight oxidative stress and prevent disease?
A: Selenium is incorporated into special proteins called selenoproteins, which support antioxidant defenses. These proteins, including glutathione peroxidase and thioredoxin reductase, neutralize harmful free radicals that cause cell damage. Without sufficient selenium, oxidative stress accelerates aging and increases the risk of chronic diseases like cardiovascular disease and cancer.
Q: What are the best dietary sources of selenium?
A: Selenium-rich foods include eggs, grass fed meats (beef and lamb), fatty fish (such as sardines), and dairy products from raw, grass fed milk. However, in regions where soil selenium levels are low (e.g., parts of Europe, China, and New Zealand), there’s a chance that dietary intake will not be sufficient, making supplementation necessary.
Q: Can selenium help prevent or treat cancer?
A: Studies show that selenium has anticancer properties, as it helps regulate proteins involved in tumor growth and drug resistance. Specific selenium compounds, such as methylseleninic acid (MSA) and seleno-L-methionine (SLM), have been shown to slow tumor growth and enhance the effectiveness of chemotherapy while minimizing side effects.
Q: Are there risks associated with selenium supplementation?
A: While selenium is crucial for health, excessive intake leads to toxicity, known as selenosis. Symptoms include brittle hair and nails, digestive issues, skin rashes, and neurological effects like irritability and fatigue. In severe cases, selenium toxicity causes organ failure. It is recommended to stay within the daily allowance (55 mcg for adults) and choose high-quality, bioavailable forms like selenomethionine.
