Selenium is a trace mineral that your body needs for protecting DNA and ensuring healthy brain function.
Scientific evidence indicates that selenium may be protective against cognitive decline, oxidative stress, and thyroid dysfunction.
If you need to boost your intake of this obscure but important nutrient, read on—our research team has ranked the ten best selenium supplements on the market.
1. Thorne Research Selenomethionine
Thorne Research Selenomethionine is the purest selenium supplement on the market when it comes to ingredients.
Aside from selenium itself, the only ingredient is the cellulose that’s used to make up the capsule. For a 200 mcg selenium supplement that makes no compromises on clean supplement design, choose Thorne Research.
2. Pure Encapsulations Selenium
Pure Encapsulations Selenium delivers the standard 200 mcg dose in a cellulose capsule, and aside from a touch of vitamin C for better shelf life, it’s devoid of additional additives, making it a smart choice.
3. Dr. Mercola Zinc + Selenium
Dr. Mercola Zinc + Selenium has a targeted formula to address some of the most common trace mineral deficiencies in elderly people.
In addition to its namesake ingredients of zinc (15 mg) and selenium (200 mcg), this supplement also includes 0.25 mg of copper, another essential trace mineral that’s increasingly important as you get older.
Though it’s not the product for you if all you want to address is your selenium levels, many users will appreciate its more holistic approach to mineral deficiencies.
4. Life Extension Super Selenium Complex
Life Extension Super Selenium Complex pairs two forms of selenium with vitamin E for added antioxidant power. This supplement is designed specifically to take advantage of selenium’s benefit for long-term well-being and youthfulness, and the inclusion of two different types of selenium might marginally improve the bioavailability of this supplement.
While the supplement design isn’t the cleanest, it’s still a solid pick for those interested in combining selenium with other powerful antioxidants like vitamin E.
5. NOW Foods Selenium
NOW Foods has, as expected for this brand, a simple and no-nonsense selenium supplement. It delivers 200 mcg of selenium per capsule, and the capsules are made of cellulose.
Aside from a bit of rice flour and stearic acid to hold the capsule together, there are no additional ingredients, making it a solid pick for those conscious about purity.
6. Zhou Nutrition Selenium
Zhou Nutrition is usually pretty innovative with their supplements, but everything about this selenium supplement is standard fare.
The dosage is the typical 200 mcg, and unfortunately, it has few extra additives like silica and magnesium stearate that you won’t find in other competitors.
7. SENSEable Supplements Selenium
SENSEable Supplements Selenium has a very particular niche use, which is for people who can’t or don’t like to take pill-based supplements.
This liquid form selenium supplement contains 156 mcg selenium in each two droplet serving, but measuring out drops with precision is difficult, so you’re not likely to get a reliable dosage.
Most people would be better suited for a different selenium supplement, but if you really want to avoid capsules and pills, or really want to be able to mix selenium into shakes, juices, or smoothies, it’s well-suited for your needs.
8. NutriONN Selenium
NutriONN Selenium has the typical 200 mcg dose of selenium, but its supplement design isn’t the cleanest. WIth additives like silicon dioxide and no real features to make it stand out from the crowd, it’s hard to rate this supplement much higher.
9. BRI Nutrition Selenium Extra Strength
BRI Nutrition Selenium Extra Strength bills itself as an extra strength supplement, but in reality, its dosage of selenium is no higher than the competition.
With fairly mediocre purity as far as ingredients, it doesn’t do much to stand apart from other products on the market.
10. Nature’s Bounty Selenium
Nature’s Bounty Selenium includes the usual 200 mcg of selenium. Its selenium is produced biologically, by specially-engineered yeast.
The presence of high levels of brewer’s yeast might cause some problems if you are trying to alter your body’s probiotic makeup, for example, you might not want to be adding yeast in the form of a supplement, even as a byproduct.
Selenium benefits and side effects
Selenium is a little-known trace mineral that helps your brain stay healthy, helps your DNA and cells avoid oxidative damage, and helps your thyroid function properly.
Though acute deficiencies in selenium are rare, emerging evidence suggests that higher selenium levels might be associated with better long-term health and cognitive function.
We’ll explore some of the evidence behind the health benefits of selenium before examining optimal dosages and potential side effects.
Selenium helps protect your body’s cells and DNA from oxidative damage. Selenium plays a very specific antioxidant role inside your body, according to a review article published in 2000 in The Lancet by Margaret Rayman at the University of Surrey (1).
The review cites dozens of studies that describe the molecular mechanisms behind selenium’s ability to protect cells in your body from oxidation.
Oxidative damage (as well as the inflammation that goes along with it) are implicated in just about every chronic disease you can think of, from heart disease to cancer to cognitive impairment in the elderly.
Selenium acts at the level of the cell membrane, protecting external free radicals from causing damage to the membrane around the cell.
Selenium may protect sperm cells against oxidative damage. One specific type of cell that seems to benefit from selenium is sperm cells in men.
A study published in 2003 in the journal Mutation Research/Genetic Toxicology and Environmental Mutagenesis found an interesting connection between selenium levels in the blood and sperm health and quality in healthy men (2).
The researchers showed that higher selenium levels in the blood were linked to less oxidative damage in sperm, and better quality and density of sperm.
This suggests that selenium might play a role in male reproductive health thanks to its antioxidant properties, and indeed, you’ll find it in a few male enhancement supplements for exactly this reason.
Low selenium levels are associated with worse cognitive function in the elderly. Selenium appears to play a role in brain function as well as in oxidative damage protection, as evidenced by several studies connecting selenium deficiency to poor cognitive performance, particularly in older people.
One such study published in 2007 in the American Journal of Epidemiology looked at levels of selenium in nail clippings (an easy to measure proxy for long-term selenium exposure) among a group of elderly people living in rural China (3). The subjects then took a battery of cognitive function tests that examined memory and learning.
When the researchers compared cognitive performance as a function of selenium levels, they found a consistent positive association between selenium levels and memory and learning performance across all but one test, providing strong evidence that high levels of selenium during your older years could protect your brain from cognitive decline.
Selenium might directly prevent degenerative diseases of the brain like Alzheimer’s. Additional evidence, both from animal studies and from humans, suggests that selenium helps protect your brain.
A study in rats published in 2009 in the journal Brain Research by scientists at Hamdard University in India provided evidence at the molecular level for the protective effects of selenium against Alzheimer’s disease (4).
Their experiment that selenium was able to significantly reduce the effects of an artificially-induced version of Alzheimer’s in male rats, and more critically, they showed that this reduction was linked to the antioxidant activity of selenium, providing a biological link between its antioxidant and its neuroprotective effects.
In humans, research published by a team of scientists from France in the journal Epidemiology showed a long-term link between selenium levels in the blood and cognitive decline (5).
They showed that long-term declines in blood levels of selenium, measured over the course of nine years, were associated with an increased risk of developing cognitive decline.
More specifically, the risk was proportional to selenium levels: the greater the decline with age, the greater the likelihood of developing cognitive decline.
Reducing chronic inflammation is likely the reason selenium appears to improve brain health. More evidence for the connection between chronic inflammation and cognitive decline came from a four year long study published in the Journal of the American Geriatrics Society (6).
The researchers followed over 1,100 healthy adults age 60 to 70 and tracked both their cognitive function and their overall level of inflammation, as assessed by a biomarker called thiobarbituric acid reactive substances or TBARS. The researchers found that the level of TBARS during the study was predictive of a subject’s risk for decreases in cognitive function compared to baseline.
Moreover, the researchers found that selenium levels were inversely associated with risk of cognitive decline: the greater a person’s selenium levels, the lesser their risk of cognitive decline.
These findings from various studies in different populations together make a robust case for the importance of selenium when it comes to preserving brain function as you get older.
Selenium plays a role in proper functioning of the thyroid gland. Initial research into the function of selenium noted that it had a particularly high concentration in the thyroid gland, suggesting that it played an important role in ensuring the proper regulation of the production of thyroid hormones.
Later work, such as an article published in the journal endocrine review by three researchers at Humboldt University in Germany, confirmed these suspicions (7).
Selenium is used in the thyroid to prevent oxidation from hydrogen peroxide, which could disrupt the synthesis of critical proteins for hormone production.
Most research to date has focused on the effects of selenium supplementation on the thyroid problems associated with acute iodine and selenium dysfunction, so it’s unclear exactly what role selenium could play in chronic hypothyroid or hyperthyroid conditions. Selenium by itself, though, does appear to increase risk for thyroid problems if taken in excess.
According to the Office of Dietary Supplements at the United States National Institutes of Health, excessive selenium intake can cause brittle nails, hair loss, a garlic-like smell in your breath, fatigue, and rashes (8).
High intakes of selenium have been studied in great detail because of the unusually high level of selenium in Brazil nuts (two Brazil nuts can contain as much selenium as a typical over the counter selenium supplement).
As a result of these studies, the Office of Dietary Supplements has set tolerable upper limits of selenium at 400 mcg per day for adult males and female.
Some research has also suggested, at least in theory, that high levels of selenium could impair ovarian function in women, though hard epidemiological evidence for this effect is not evident yet (9).
Some epidemiological studies have also found an increased risk for type 2 diabetes in people with higher selenium levels than average (10), and selenium by itself can dominate the function of iodine in the thyroid gland, leading to thyroid problems (11). These seem to appear at intakes greater than 300 mcg per day.
Given the upper limits discussed above, it should be no surprise that the vast majority of over the counter selenium supplements have 200 mcg of selenium each.
Taking one of these capsules per day should be enough to boost your selenium without putting you over the daily limit, unless you consume a lot of foods rich in selenium. This is also in line with the dosage level used in many clinical studies.
Selenium is an important trace mineral that’s associated with increased resistance to oxidative damage, improvements in brain and thyroid health (in moderate amounts), and protection against cognitive decline in the elderly.
Selenium levels drop over time as you get older, so increasing your selenium intake appears to be a priority particularly for people who are age 60 and older.
There are some risks associated with chronically high selenium intake, so supplementation is only the right choice if you know your dietary intake is low.
Typical clinical trials use doses of 200 mcg per day, taken in one single dose, and this is in line with what’s available in a supplement bought over the counter.
When used by the right people in the right circumstances, selenium could help boost your resistance to oxidative damage, chronic inflammation, and losses in cognitive function.