A Registered Dietitian Explains the Many, Many Benefits of Selenium—And How To Know Your Limits

Photo: Getty Images / Claudia Totir
Certain things in life are just better together: chocolate and peanut butter, you and your BFF, iron and vitamin C. Another power duo that deserves major recognition is selenium and antioxidants. Selenium might sound like a substance akin to Superman's dreaded kryptonite, but don't worry–it's actually good for you (and won't zap you of your powers). The National Institutes for Health reports that selenium is a nutritionally essential nutrient that benefits reproductive health, thyroid function, and DNA production and supports protection from infection and damage from free radicals. Whew, that's a mouthful. Don't worry; we will dig deeper into what this actually means, foods high in selenium, how much selenium you need per day, selenium deficiency symptoms, selenium toxicity signs, and excellent sources of selenium.

If you've seen a TikTok promoting the benefits of selenium-rich Brazil nuts, you probably have been asking yourself, okay, woah, what is selenium? While not given as much press time as magnesium or calcium, selenium is another essential trace mineral that your body needs to be in tip-top shape. It's found in soil, water, and foods like brazil nuts, eggs, tuna, cod, poultry, and mushrooms. While overdoing it on selenium can be dangerous (more on that later), for the most part, selenium can work wonders for the human body. Here's everything you need to know about this super mineral.

The Top Health Benefits of Selenium

1. It helps antioxidants do their job.

"In humans, selenium functions as a cofactor for antioxidant enzymes, including glutathione peroxidase, whose main role is to protect our tissues from oxidative damage," says nutritionist Tamar Samuels, RDN. Basically, your body needs selenium in order to get the most benefits out of certain antioxidants that fight inflammation and free radical damage in your body.

2. It's important for a healthy immune system.

The mineral also helps facilitate cell growth, says Samuels, and is an important part of immune system health. "Selenium is also needed for the proper functioning of neutrophils, macrophages, NK cells, T lymphocytes, and other immune mechanisms." All of these parts play an important role in protecting your body from infection and disease. Take that, cold season.

3. It may boost thyroid health.

Selenium helps your body metabolize thyroid hormones, which help regulate your metabolism, digestive function, and mood. For anyone who's ever struggled with thyroid issues, you may want to allow selenium to be your new best friend—because it can help a lot. "Clinical research shows that selenium taken in combination with thyroid medication helps to lower autoimmune thyroid antibodies," says Samuels. She says the mineral might also help improve postpartum thyroid function.

4. It might help fight cancer.

Remember how selenium helps antioxidants do their job? That may translate into some cancer-fighting benefits, too. "Selenium may reduce the risk of colorectal cancer," says Samuels—although a 2016 study found that the mineral offers only moderate benefits in this area. She also notes one study which found that selenium may decrease cancer risk and overall mortality in men.

What are the signs of selenium deficiency?

Selenium is not as straight forward of a nutrient as something like vitamin D or vitamin C, where low levels have very obvious characteristics that are easily traced back to their cause. Maybe this is because those nutrients are just more well known, but the following are some symptoms of selenium deficiency, according to Harvard's School of Public Health.

  • Weakened immune system: Selenium is essential for optimal immune system function. Therefore, if you're not getting enough selenium, you may find yourself getting sick more often or experiencing more severe symptoms when you do get sick.
  • Fatigue: Selenium s important for energy production, so a deficiency can lead to feelings of tiredness and exhaustion.
  • Cognitive struggles and mental fog: Some studies have linked selenium deficiency to cognitive decline and an increased risk of dementia.
  • Thyroid problems: Selenium plays a crucial role in thyroid hormone metabolism, so a deficiency can lead to thyroid problems such as hypothyroidism.
  • Hair and nail changes: Selenium is important for healthy hair and nails, so a deficiency may result in brittle nails, hair loss, or changes in hair texture.
  • Infertility: Selenium is important for the production of sperm, so low selenium levels can show up in reduced signs of fertility, especially in men.

If you're experiencing any of these symptoms, it's important to speak with your healthcare provider. They can perform a blood test to determine your selenium levels and recommend appropriate treatment if a deficiency is identified.

What foods are high in selenium?

According to the Harvard School of Public Health, soil levels and environmental factors contribute to whether foods are high in selenium. Many animal proteins such as seafood, meat, organ meat, and eggs are common sources of selenium. North American soil is typically rich in selenium, but many everyday staples, like breads and cereals, are often fortified with necessary vitamins and minerals, including selenium.

If you're considering a selenium supplement, try to start in your kitchen first. This is because eating foods rich in selenium is the best way to hit the recommended amount, says Stephanie Middleberg, MS, RD, CDN, a nutrition expert for Provenance and founder of Middleberg Nutrition.

Because selenium is so commonly found in animal products, people that are vegetarian or vegan are encouraged to be aware of their diets to avoid selenium deficiency.

While selenium supplements are available, experts always encourage the acquisition of your nutrients through food. So, now that we have answered the question of what selenium is let's dig into what foods are high in selenium.

  • Brazil nuts: Brazil nuts are one of the best sources of selenium, according to the NIH. Just one ounce (or about 6-8 nuts) provides over 500 percent of the recommended daily intake. In that vein, Harvard's School of Public Health recommends that one should stick with ½ a brazil nut since too much selenium can be harmful to you.
  • Seafood: Many types of seafood are rich in selenium, including tuna, salmon, sardines, and shrimp, the NIH reports.
  • Poultry and red meat: Chicken and turkey are both good sources of selenium, especially when the meat is from organic and/or pasture-raised animals. Additionally, organ meat and red meat are also good sources of selenium, says the NIH.
  • Whole grains: Whole grains such as oats, brown rice, and whole wheat bread are good sources of selenium, as well as other important nutrients. This is both because some of these products are fortified with nutrients needed in the diet and naturally occurring selenium, according to the NIH.
  • Eggs: Eggs are a good source of selenium, as well as other nutrients such as protein and healthy fats.
  • Dairy products: Some dairy products, such as cheese and milk, contain small amounts of selenium.

While it's important to consume enough selenium, it's also important not to consume too much, says Middleberg.

Is there such a thing as too much selenium?

In a word, yes. The recommended daily allowance (RDA) of selenium is 55 milligrams per day, although a 2012 study found that most people get more than they need from diet and supplementation. People can safely take up to 400 milligrams per day, says Samuels, but anything more than that can be harmful. Consuming too much selenium is linked with a number of health consequences, she says, including nausea, vomiting, abdominal pain, dermatitis, nail changes, fatigue, irritability, alopecia, impaired endocrine function, neurotoxicity, and weight loss. Too much selenium can definitely lead to selenium toxicity which means that one should be careful with supplementation.

And if you suffer from an autoimmune disease, be careful. "Selenium might have immunostimulant effects, meaning it could worsen an autoimmune disease by stimulating disease activity," says Samuels.

Another thing to be wary of? Adverse effects on male fertility. "High amounts of selenium, including through getting it through diet, might decrease sperm motility, potentially impacting male fertility," explains Samuels. How much selenium you need in a day is dependent on your lifestyle and diet. Talking with a trusted provider if you're not sure if you're getting enough is a great place to start in order to prevent both selenium deficiency and selenium toxicity.

So if you're already getting a lot of selenium through your diet (like eating lots of poultry and eggs), it may be best to keep it that way to avoid overdoing it. A separate selenium supplement probably isn't necessary for most people unless their doctor recommends it.

Is selenium good to take daily?

In the same vein of the question, "is there such a thing as too much selenium" you might be wondering if selenium is good to take daily. The answer is multifold, but Middleberg shares that since there are so many foods high in selenium, most people will not need to take a selenium supplement.

The recommended daily intake of selenium varies depending on how old you are, but by and large, the National Health Institutes recommend 55 mcg per day. This could change, however, based on a number of health conditions. Some communities with low levels of selenium in their soil may benefit from more to prevent selenium deficiency.

Just remember that the tolerable upper intake level for selenium is set at 400 mcg per day for adults, and exceeding this amount can lead to toxicity symptoms such as hair loss, gastrointestinal upset, and neurological damage, according to the NIH.

FAQs About the Benefits of Selenium

Who should not take selenium?

Although selenium is important for fetal development and breast milk production, taking too much selenium can be harmful to both the pregnant person and their baby, according to the Mayo Clinic. Pregnant or breastfeeding people should speak with their healthcare provider to determine the appropriate amount of selenium to consume.

Children have smaller bodies and lower tolerances for nutrients than adults, so high doses of selenium can be especially harmful. Children should not take selenium supplements unless specifically directed by a healthcare provider, according to the Mayo Clinic.

Some people may be sensitive to selenium and may experience symptoms such as rash, itching, or gastrointestinal upset. If you experience any of these symptoms after consuming selenium-rich foods or supplements, stop taking them and speak with your healthcare provider.

Some medications can interact with selenium, the Mayo clinic shares, including blood thinners and cholesterol-lowering medications. If you are taking any medications, speak with your healthcare provider before taking selenium supplements.

In general, it's always a good idea to speak with your healthcare provider before taking any supplements or making significant changes to your diet. They can help you determine the appropriate amount of selenium to consume based on your individual needs and health status.

Does selenium include better help you sleep?

There are some supplements and nutrients that tout sleep benefits, like magnesium. Magnesium does, in fact, help you sleep. Not all rumors are true, though, and selenium really doesn't have direct sleep effects, according to the NIH.

However, getting all of your essential nutrients is important and can secondarily support quality sleep. Selenium is important for energy production, and a deficiency can lead to feelings of tiredness and exhaustion, according to the Mayo Clinic. Therefore, getting enough selenium may help combat fatigue and promote better sleep. Additionally, selenium is important for immune system function, and a strong immune system can help promote good health and sleep.

Can you take zinc and selenium together?

Yes, according to the Journal of Cancer Prevention, you can consume zinc and selenium together, in fact there are benefits to getting enough of both because they do work together. In fact, both zinc and selenium are essential minerals that play important roles in the body's immune system function and overall health.

Zinc is important for immune function, wound healing, and DNA synthesis, while selenium is important for thyroid hormone metabolism and antioxidant defense. Both minerals also play a role in maintaining healthy skin, hair, and nails and fighting against infections and free radicals.

However, one thing to note is that both zinc and selenium have levels of diminishing returns when it comes to supplementation. There is a risk of harm past a certain level of dosage, so both should be monitored at safe levels. Overall, selenium, when consumed at the right amount, has a plethora of benefits. Kudos to you for doing more research on how to have the healthiest diet for your body.


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