The Health Benefits of Selenomethionine

Important for Thyroid Function, Reproduction, and DNA Production

Selenomethionine (Se-met) is one of the main natural food forms of selenium. As a form of selenium, it is important for normal thyroid gland function, reproduction, DNA production, and protecting the body from infection. It has been studied for other health benefits for the thyroid, heart, and more.

It is a selenoamino acid that is the selenium analogue of methionine. It has a role as a plant metabolite. When taken as a supplement, selenomethionine is either converted directly to selenium or is stored in place of methionine in body proteins. 

Selenomethionine metabolism is closely linked to protein turnover. It combines with proteins in the body to form antioxidants called selenoproteins, which help protect the cells in your body from damage by free radicals.

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Health Benefits

Selenomethionine has been studied for its role in thyroid disease, cancer, and heart disease prevention, as well as preventing cognitive decline.


In the body selenium levels are highest in the thyroid gland, having important functions in thyroid hormone production and metabolism. Because of this, selenomethionine supplementation has been studied for its effects on diseases of the thyroid.

A randomized controlled prospective study of 192 people with mild subclinical hypothyroidism due to Hashimoto’s thyroiditis received either oral selenomethionine treatment (control) or a placebo for four months.

At the end of the study, 31.3% of control participants restored euthyroidism, compared to 3.1% in the placebo group. This study showed that selenomethionine supplementation could potentially restore normal thyroid levels in people with autoimmune thyroiditis.

Another study looked at how children and adolescents with autoimmune thyroiditis would respond to selenomethionine supplementation. Seventy-one participants were randomized to receive selenomethionine or placebo daily for 6 months.

At the end of the study, a statistically significantly higher reduction in antibodies against thyroglobulin (anti-Tg) was observed in the selenomethionine group compared to the placebo group. showing that selenomethionine supplementation appears to reduce anti-Tg levels in children and adolescents with autoimmune thyroiditis.

In addition, a randomized, double-blind, placebo-controlled trial looked at whether selenomethionine had a protective effect against thyroid autoimmunity during and after pregnancy. Researchers randomly assigned 45 women with thyroiditis in pregnancy to receive either selenomethionine or placebo. They were evaluated around 10 weeks gestation (T1), 36 weeks gestation (T2), and 6 months after delivery (PP). 

There were no significant differences between the groups at T1, however the researchers saw a significant increase in selenium blood levels in the selenomethionine group at T2, and a significant reduction of autoantibodies after delivery in the selenomethionine group.

We may assume from these three studies that selenomethionine supplementation might be beneficial for conditions of the thyroid in various subgroups of people, including adults, pregnant women, children, and adolescents.


The Adenomatous Colorectal Polyp (ACP) study was designed to see whether selenium (as selenomethionine) or vitamin E reduced the prevalence of colorectal adenomas and cancers. The participants were 2,286 men with one or more adenomas in the colon.

In the men who received selenomethionine 34.2% or placebo were diagnosed with adenomas at least 12 months after randomization compared to 35.7% in those who received placebo. This was not significant and demonstrated that selenomethionine supplementation had no effect on cancer prevention in the colon in these patients.

A 2018 review of previous studies also found that taking selenium, including in the form of selenomethionine, did not have an impact on any type of cancer risk.

Heart Disease

A 2015 review that examined selenium as it relates to heart disease risk found an inverse relationship with selenium intake and heart disease. Yet, when researchers reviewed previous studies that looked at selenium supplements, they were unable to determine if it was selenium supplements alone that actually prevented heart disease.

The researchers also reported that selenomethionine is one of the most effective organic forms of selenium for improving selenium status. However, though it isn’t as acutely toxic, selenomethionine is a less-efficient metabolic source compared to other inorganic forms of selenium because it needs to be reduced and is not available for intravenous therapy. 

To date, the insufficient and inconclusive clinical-trial evidence does not support the use of selenomethionine supplements for preventing heart disease, especially in healthy people who already get enough selenium from their diet.

More clinical trials are needed to better understand the relationship between selenomethionine supplementation and cardiovascular disease risk.

Cognitive Function

Selenium levels in the body have been observed to decline with age. Because of this, low or deficient selenium may be associated with age-related cognitive declines, possibly due to decreases in selenium’s ability to act as an antioxidant. 

However, results of observational studies are mixed with no clear evidence for selenium’s role, in the form of selenomethionine and others, in the treatment of Alzheimer's disease, but recognize that it may have potential for prevention.

More studies are needed to determine whether selenomethionine supplements are beneficial for preserving cognitive function in elderly people.

Possible Side Effects

The tolerable upper dietary intake level for selenium is 400 micrograms per day for adults.

Signs and symptoms of excess selenium intake (selenosis) include garlic breath odor, a metallic taste in the mouth, hair loss, nail brittleness, blotchy teeth, nausea, diarrhea, skin rashes, fatigue, irritability, and nerve damage.

Always talk with your healthcare provider before taking large doses of any dietary supplement, including selenomethionine, and follow the directions on the product label.

Dosage and Preparation

There are no recommended dosages for supplemental selenomethione. Selenomethionine supplements are most commonly available in the form of tablets or capsules, with usual dosage amounts of 200 micrograms.

The National Academies of Sciences sets the Dietary Reference Intakes (DRIs) for vitamins and minerals, including selenium. The DRIs for selenium are based on age, as well as life stage, including people who are pregnant or breastfeeding. The DRIs include your intake from all sources (i.e. food, drinks, and supplements).

Dietary Reference Intakes for Selenium

The DRI for different groups include:

  • 1 to 3 years: 20 micrograms per day
  • 4 to 8 years: 30 micrograms per day
  • 9 to 13 years: 40 micrograms per day
  • 14+ years: 55 micrograms per day
  • Pregnancy: 60 micrograms per day
  • Lactation: 70 micrograms per day

What to Look For

Selenomethionine is a common supplemental form of selenium. Dietary supplements, including selenomethionine, are not regulated by the Food and Drug Administration (FDA) or any other governmental agency. Because of this, available supplement products can vary greatly in quality and effectiveness.

Simply reading the label may not provide enough information to make a well-informed buying decision on supplements such as selenomethionine. It’s best to ask your doctor and pharmacist for help in choosing the right supplement for you.

They can guide you toward the best dosage for your needs and recommend a trustworthy product certified by a third party to ensure quality, such as the U.S. Pharmacopeia, NSF International, or Consumer Lab. 

Other Questions

Can I get selenomethionine from foods?

Most dietary selenium is in the form of selenomethionine or selenocysteine. Selenium is found in many foods, such as nuts (especially Brazil nuts), seafood, organ meats, whole grains, meat, poultry, eggs, and dairy.

Selenium concentrations in foods, especially plant-based, vary widely depending on the location from where it was sourced. The concentration of selenium in plant-based foods depends on the amount of selenium in the soil, as well as if the form of selenium is responsive to plant uptake, the amount of organic matter in the soil, and soil pH.

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