Selenium’s Benefits: Free Radical Reduction and Cancer Prevention

Bioavailability, requirements, drug interactions, and more

By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital
Edited by Kate Findley and proofread by Angela Shoemaker, Wondrium Daily

The popularity of selenium supplements has been on the rise at health food stores. Professor Anding dives into the research to investigate the benefits of this mineral. Also, where do you find selenium in natural sources?

Foods high in selenium
Derived from food sources such as Brazil nuts, seafood, organ meats, cereals, grains, and dairy, selenium is a powerful antioxidant. Photo By Yulia Furman / Shutterstock

Selenium Benefits and Bioavailability

The primary benefit of selenium is to reduce peroxide free radicals, which are believed to cause aging and various forms of cancer. Research has shown both benefits and risks associated with this mineral. It works synergistically with vitamin E as an antioxidant and plays a valuable role in thyroid function.

When it comes to bioavailability, plants are the most common dietary source of selenium. The amount of selenium that you absorb from eating plant products depends on how much mineral was in the soil where the plant was grown. 

If the plant was grown in selenium-deficient soil, the food itself is going to be deficient in selenium. In the United States, the selenium content, or the concentration in that plant, can vary almost 200-fold from region to region. 

If you are growing a large garden to harvest your own food, you might not have adequate amounts of selenium in your soil, and should get your soil tested. If you are specifically interested in selenium content, meat and poultry tend to be a more reliable source of selenium, since their feed is typically supplemented with this mineral. 

However, as the organic and sustainable movement has grown, more animals are raised free-range or grass-fed. As a result, their food source of grass has to have an adequate amount of selenium.

Meanwhile, the balance of other nutrients in a person’s diet can decrease the absorption of selenium, and absorption of zinc, illustrating the importance of balance: high doses of iron, vitamin C, and heavy metals all affect absorption.

“Your body loves to drive down the middle of the road,” Professor Anding said. “When I decide to take it into the ditch, there are going to be health consequences to pay.” 

Selenium Requirements

The dietary reference intake of selenium for adults is about 55 micrograms (mcg), with the upper limit being 400 mcg. Dietary sources of selenium are plentiful: a quarter of a cup of Brazil nuts has 1,036 mcg, oysters have 116 mcg per a 2.5-ounce serving, a cup of cooked oatmeal has 19 mcg, and a medium-sized boiled egg has 13 mcg.

Interestingly, research on the benefits of selenium has been mixed. The “SELECT Study” was designed to see the effects of selenium and other antioxidants on the prevention of prostate cancer. After 5.5 years, the intervention group showed no difference from the control group. 

However, a correlation exists between selenium levels in the blood system along with a C‑reactive protein, which is a measure of inflammation. The higher your C-reactive protein, the greater your body’s inflammatory response.

In some studies, a higher selenium level was associated with a lower C-reactive protein, suggesting that selenium may reduce inflammation. This is important information because an inflammatory response is thought to contribute to heart disease and cancer. 

Supplements and Drug Interactions

Beyond studies related to heart disease, the science community has shown an ongoing interest in selenium supplementation in regard to immunity. The original selenium interest surfaced when about 180 men with HIV had a reduction in hospitalization occurrences while regularly taking 200 mcg of selenium. This data led to a resurgence in selenium supplementation for immune function.

Studies show that selenium supplementation may offer some protection from basal cell carcinomas, but may contribute to an increased risk for squamous cell skin cancer. Understandably, this is a bit confusing.

The take-home point of all these research studies is to concentrate on selenium-rich foods as opposed to supplements.

Selenium deficiency has been rare in the United States, where selenium intake is typically 100 to 250 mcg per day, but it’s on the rise again. As the number of Americans going for gastric bypass surgery increases, cardiomyopathy—the heart disease associated with selenium deficiency—is on the rise. 

Important to keep in mind, you should be aware of selenium and drug interactions. Chemotherapeutic drugs, for example, may increase selenium requirements. On the other hand, selenium may reduce the effectiveness of statin resins that are used to lower cholesterol. 

Toxicity can exist, but it’s usually at doses greater than 900 mcg per day. Some concern exists that increased levels of selenium may increase the likelihood of glucose intolerance, which is a precursor of diabetes. However, if you are getting your selenium primarily from dietary sources, toxicity will likely not be a concern.

This article was edited by Kate Findley, Writer for Wondrium Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for Wondrium Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.