Selenium – Review the Latest Research

Full Disclosure


Selenium is an essential mineral found naturally in various foods and is included in other food items. It can also be purchased as a nutritional supplement. Selenium is one of 25 selenoproteins. These include glutathione peroxidases, thioredoxin reductases, and selenoprotein P. Selenoproteins play an important role in thyroid hormone metabolism reproduction, DNA synthesis, and protection against infections and oxidative damage.

Groundwater and soils are sources of inorganic selenium (e.g., the selenites, selenites, or selenates) that plants build up and transform into organic forms, most notably selenium and selenocysteine, as well as their methylated derivatives. Selenium can be primarily present in food items such as selenomethionine with selenocysteine. Selenium in the diet is easily absorbable by the body. Its absorption is generally not affected by selenium levels.

Inorganic selenium and selenomethionine that are absorbed are quickly metabolized into an ordinary intermediate used to produce selenocysteine selenium's form, which is found in selenoproteins in the human body. Between 28% and 46 percent of the selenium in the body is located in skeletal muscles. Selenium homeostasis is primarily maintained through the excretion of urine and, in the case of higher intakes, via the lungs and the feces.

The most widely used measures of selenium levels are serum and plasma levels. Serum or plasma selenium concentrations of 8 milligrams (mcg)/dL or more in healthy individuals are considered adequate for producing selenoproteins. The serum, plasma, and urine concentrations indicate the amount of selenium consumed in the last few days. In contrast, selenium levels in blood samples (including erythrocytes) indicate long-term conditions. Analyses of nail and hair selenium levels are also used to track long-term intakes over months or even years.

The two most prevalent selenoproteins within plasma are glutathione Peroxidase 3 and selenoprotein P, and both can serve as biomarkers for selenium levels. But, some question the validity of both biomarkers as indicators of the presence of selenium deficiencies because selenoprotein levels can be affected through oxidative stress and inflammation. Furthermore, studies suggest that supplementing with selenium does not improve the selenoprotein P level or glutathione peroxidase activities unless people suffer from selenium deficiency. Selenometabolites that are methylated in the urine are not reliable biomarkers of selenium status because most people cannot methylate enzymes because of genetic variations.

Recommended Intakes

Selenium intake recommendations and other nutrients are given in Dietary Reference Intakes (DRIs) created in collaboration with the Food and Nutrition Board (FNB) in the National Academies of Sciences, Engineering, and Medicine. DRI is the generic term for a set of reference values for planning and assessing the intake of nutrients for healthy individuals. These values, which differ depending on age and gender and gender, include:

  • Recommended Dietary Allowance (RDA): Average daily intake that is adequate to meet the nutritional needs of almost all (97%-98 percent) healthy individuals. Typically used to design nutritionally balanced diets for people.
  • Affordable intake (AI): Intake at this point is considered to guarantee nutritional sufficiency and is established when evidence is insufficient to determine an RDA
  • Estimated Average Requirement (EAR): The average daily intake of nutrient levels that is believed to meet the needs of 50 percent of healthy individuals. It is generally used to determine the intake of nutrients for groups of people and plan healthy diets that are nutritionally appropriate for them. It may also be used to determine the nutritional intake of individuals.
  • The Tolerable Level of Upper Intake (UL): Maximum daily intake is not likely to cause adverse health effects.

Recommended Dietary Allowances (RDAs) for Selenium

  • From birth to 6 months

    • Male: 15 mcg
    • Female: 15 mcg
  • 7-12 months

    • Male: 20 mcg
    • Female: 20 mcg
  • 3 to 5 years

    • Male: 20 mcg
    • Female: 20 mcg
  • 4-8 years old

    • Male: 30 mcg
    • Female: 30 mcg
  • 9-13 years old

    • Male: 40 mcg
    • Female: 40 mcg
  • 14-18 years old

    • Male: 55 mcg
    • Female: 55 mcg
    • Pregnancy: 60 mcg
    • Lactation: 70 mcg
  • 19-50 years old

    • Male: 55 mcg
    • Female: 55 mcg
    • Pregnancy: 60 mcg
    • Lactation: 70 mcg
  • 51plus years

    • Male: 55 mcg
    • Female: 55 mcg

Sources of Selenium

Since selenium is bound to protein, food items with high protein content are usually the most potent Selenium sources. Brazil's seafood, nuts, poultry, meat, and organ and marrow meats are among the highest sources of selenium from food. Others include cereals, other grains, and dairy products. The selenium in drinking water isn't vital for health in many regions. The primary food sources of selenium in Americans' diets in the United States are bread, grains, poultry, meat, seafood, eggs, and other foods.

Selenium content in a particular type of plant-based food is determined by the quantity and nature of selenium present in the soil and other variables, including soil pH and the amount of organic matter present in the soil. Ultimately, selenium levels in plant-based food products differ according to geographic location. For instance, according to FoodData Central from the U.S. Department of Agriculture (USDA), Brazil nuts have 544 mcg of selenium per ounce; however, the results from other analyses differ significantly.

The content of the soil in selenium influences how much selenium is present in the animal's diet. However, this doesn't much affect the amount of selenium found in animal products since animals maintain consistent levels of selenium in their tissues through homeostatic mechanisms. In addition, the formulation of livestock feeds typically contains selenium in inconsistent levels.

*DV = Daily Value. The U.S. Food and Drug Administration (FDA) came up with DVs to assist consumers in comparing the nutrient content of foods and supplements to their diets in the context of a complete diet. Selenium's DV is 55 mg for adults and children four years or older. FDA doesn't require labels on food products to include selenium content, except if selenium has been added to the food item. Foods that contain 20 percent or more of DV are considered significant sources of nutrients; however, foods that contain less than 20% of DV are also a part of healthy eating. The USDA's FoodData Central lists the nutrient contents of many food items and a complete list of foods that contain selenium. It is arranged by the nutrients and also by name.

Dietary Supplements

Selenium is found in multivitamin/mineral supplementation, supplements that contain vitamin E and other ingredients, as supplements on their own. The most common forms are selenomethionine, the selenium-enriched form of yeast (grown in a high-selenium environment and is primarily the selenomethionine), sodium selenite, and sodium selenate. Selenium levels in multivitamin/mineral supplements differ, but most contain 55 mg. Selenium content is usually more incredible in supplements containing smaller ingredients. For instance, supplements containing selenium and vitamin E or other ingredients typically include between 50 and 200 mcg of selenium. Selenium supplements usually contain 100 to 400 mg.

Our bodies take around 90% selenium from selenomethionine and yeast, which are selenium-enriched, selenite, and selenate.

Selenium Intakes and Status

The majority of Americans in the United States consume adequate amounts of selenium. Furthermore, between 17% and 19% of Americans take a dietary supplement that contains selenium.

Based on an analysis of the data of the period from 2017 to March 2020 National Health and Nutrition Examination Survey (NHANES) according to the NHANES, the average daily intake of selenium for people aged 2 years and older from beverages and food is 108 mg and that from beverages, foods or supplements is around 116 mg. Men of adulthood are more likely to consume more (132 milligrams from foods and drinks and 145 mg from beverages, foods, and supplements) than women in their 20s (94 mg from food and beverages, and 102 mcg from drinks, food, and supplements).

Selenium intakes in the diet are similar for Black and White people. However, individuals who adhere to the vegetarian or vegan diet routine might have lower intakes of selenium than other people.

Based on a study of NHANES data from 2011 to 2016, the median serum selenium level for males and females aged 8 to 80 is 12.7 milligrams/dL. The research suggests that men have significantly higher levels of selenium in their blood than women and White people have higher levels than Black people. Selenium levels are lower in those who smoke, possibly because smoking causes oxidative stress.

Selenium intakes, and serum concentrations across the United States and Canada vary to a certain degree depending on the region due to variations in the amount of selenium found in soils and local food items consumed. For instance, those living in the Midwestern and Western United States have higher concentrations than those living in South and Northeast areas. However, the vast transport of food across the United States typically allows people who live in areas with low levels of selenium to have sufficient levels.

Selenium Deficiency

Selenium deficiency by itself is rarely the cause of obvious illness; however, it can trigger biochemical modifications that may make people more vulnerable to stress and develop a variety of illnesses. For instance, Keshan disease is an end-of-life cardiomyopathy, first discovered in 1935 in regions of China where the soil was deficient in selenium. Adults living in these regions were consuming selenium at an average of not over 10 mg/day. However, consuming at least 20 mg/day can protect adults from the illness. Keshan disease is most prevalently affecting pregnant women and children in preschool. While the prevalence of the disease is decreasing, the condition is present. The cause of Keshan's disease is not known. However, the incidence of the disease drastically decreased following several major interventions from the late 1970s and early 1990s that offered selenium selenite supplementation. A systematic review in 2018 with meta-analysis and review of the results from 41 research studies revealed that supplements with selenium (doses not recommended) lower your risk for Keshan Disease by 86%.

Selenium deficiency can also be related to Kashin-Beck syndrome, an osteoarthritis form most often seen during puberty and childhood. It is seen in certain low-selenium or low-iodine zones, including China, Tibet, Siberia, and North Korea.

Selenium deficiency can exacerbate Iodine deficiency, which could increase the risk of hypothyroidism congenital in infants. Endomic myxedematous hypothyroidism can be described as a disease that manifests in areas that have deficient levels of selenium, including Central Africa, and is thought to develop during pregnancy or in the early first year of childhood. People suffering from this disorder produce inadequate thyroid hormone and have deficient levels of plasma triiodothyronine (T3) and Thyroxine (T4) levels, as well as very large thyroid stimulating hormone (TSH) levels.

Groups at Risk of Selenium Inadequacy

Selenium deficiency is extremely rare across this region of the United States and Canada. However, certain people, such as those who live in different countries, may not receive enough selenium. The groups listed below are among those most likely to suffer from inadequate selenium consumption.

People living in areas with selenium deficiency

The intake of Selenium within North America, even in areas with low levels, is over the RDA because most people eat food that comes across a broad geographic region. However, those in certain countries with a diet mainly of low-selenium vegetable regions are more susceptible to deficiencies. The most selenium-rich areas worldwide are found in a few regions of China where large portions of the population eat an essentially vegetarian diet, and the soil selenium levels are deficient. Selenium intakes, on average, are lower in certain European countries, particularly among those who follow vegan diets. While the intakes of New Zealand were low in the past, they increased following the country's increase in its importation of high-selenium grains.

People undergoing kidney dialysis

Selenium concentrations are usually significantly lower for patients who are on long-term hemodialysis than for healthy individuals, partly because the hemodialysis process removes some selenium from blood. Furthermore, hemodialysis patients are susceptible to an inadequate intake of selenium from their diet due to anorexia caused by the uremia condition and diet restrictions. But, whether the selenium levels are sufficient for hemodialysis patients depends on each individual's selenium levels. For instance, the median selenium levels were higher than the 95th percentile of the normal (average benchmark: 9.2 mg/dL) at the time of baseline. They continued to be higher in a prospective 2-year study of 198 patients on hemodialysis within Western Canada. While selenium supplementation can increase blood levels in patients on hemodialysis, more research is needed to determine if the supplements are beneficial to clinical outcomes in the patients.

People who live with HIV

Patients with HIV are often found to have low levels of selenium, likely due to malnutrition or insufficient intake of selenium. The incidence of selenium deficiencies among people with HIV differs by country and is a reflection of the different selenium levels within the soil. Studies conducted on observation have revealed a connection between lower levels of selenium for people suffering from HIV with an elevated risk of having cardiomyopathy as well as a worsening progression of the disease or death, and in women who are pregnant, HIV transmission to offspring and the early deaths of the offspring. However, studies conducted in a randomized fashion suggest that the supplementation of selenium has no impact on HIV progress or treatment.

Selenium and Health

This section is focused on six conditions and diseases where selenium could have a role to play: cardiovascular disease, cancer, cognitive decline, Alzheimer's disease, HIV infection, as well as male fertility, and thyroid disease.


Because of its impact on the repair of DNA, apoptosis, and the endocrine and immune systems, in addition to other mechanisms such as its antioxidant properties, Selenium is believed to play a part in preventing cancer. Studies on animals also suggest that selenium could be a chemopreventive agent. Researchers have investigated Selenium's effects, primarily for breast, prostate, and lung cancers, as well as colorectal cancers, and prostate cancer is the most examined.

Research on epidemiology has suggested an inverse relationship between selenium levels and the possibility of prostate, colorectal, and bladder cancers, as well as lung, skin, esophageal, and gastric cancers. Additionally, a handful of studies conducted in the early stages of clinical trials showed that supplements with selenium reduced the risk of certain types of cancer. However, more recent studies haven't proved this.

It was the Nutritional Preventing Cancer Study that started enrollment in 1983. It was a randomized controlled study that examined 200 mg/day of selenium in selenium yeast or placebo for an average of 4.5 years for 1,312 men and women from the United States with histories of nonmelanoma skin cancer. While selenium supplementation didn't lower the risk of recurrence for nonmelanoma skin cancers, a study that was a follow-up discovered that those who consumed selenium had a lower risk of developing prostate cancer than the men who were on placebo for a median time of 7.5 years. The benefit was greatest in those with the lowest selenium levels in the blood (below 10.6 mg/dL), but there was no change in men with selenium levels higher than 12.3 mg/dL.

The follow-up Selenium and Vitamin E Cancer Prevention Trial (SELECT) did not conclude that selenium supplementation decreased the risk of developing prostate cancer. The controlled, randomized study of 35,533 men 50 or over from all over the United States, Canada, and Puerto Rico was discontinued after 5.5 years of analysis when it was discovered that there was no correlation between the risk of prostate cancer and a daily dose of 200 mg selenium selenomethionine, as well as without 400 units of international (IU)/day Vitamin E. A further 1.5 years of monitoring data for subjects after stopping supplementing with the study ingredients confirmed the absence of any significant relationship between selenium supplements and the risk of prostate cancer. Additional analysis of a case-cohort of 1,739 men with prostate cancer and 3,117 control subjects in the SELECT study found that supplementation with selenium did not alter the risk of developing prostate cancer for those with a low selenium level at baseline (based on the levels of selenium in toenails). However, researchers did discover a higher risk of developing prostate cancer with high-grade who have a higher selenium level at baseline (more than the 60th percentile for toenail selenium) and suggested that those older than 55 years of age stay clear of supplementing with selenium in amounts that are higher than recommended daily intakes.

The 2017 Cochrane Review on selenium for cancer prevention contained the results of 83 studies (including the ones mentioned in the previous paragraphs). Within the 70 cohort studies of observation that were reviewed, those with the highest selenium status at baseline had a 28% lower risk of cancer risk and 24% lower mortality rate from cancer than those with the lowest selenium status. Additionally, those with the highest selenium status had the lowest risk of 33% of bladder cancer, an 18 percentage reduced risk of developing lung cancer, an 18 percentage lower risk of colorectal cancer, for males with a lower risk of prostate cancer, 16% less chance of developing prostate cancer. The researchers found no connection between selenium levels in women and the risk for breast cancer. However, due to the significant flaws in the study's design, confounding factors, and difficulties in assessing selenium levels, the certainty of the findings was extremely small. Furthermore, there was no evidence for any dose-response correlation between selenium status and risk of cancer was found.

The 10 placebo-controlled, randomized studies reviewed within the latest Cochrane Review included a total of 27,232 participants, with 94 percent of them were men. Results of these studies demonstrated an increase in 200 – 500 mg/day of selenium, primarily as selenomethionine, for between 2 and 10.3 years had minimal to any effect on the incidence of cancer or death. The evidence's reliability was high for colorectal, prostate, lung, prostate, and bladder cancers. It was moderate for nonmelanoma and breast skin cancers. Most studies utilized 200 mg/day selenium, but the researchers concluded that 200 mg/day selenium doesn't reduce the risk of all cancers or the risk associated with specific cancer kinds. Additionally, they concluded further research is required to find out if supplementing selenium could reduce the risk of cancer for those with certain genetic or nutritional conditions or if different types of selenium exert different effects.

Since 2003, the FDA granted two health benefits that qualified some scientific evidence suggesting that selenium intake “may lower risks associated with certain types of cancer” and “may cause anti-carcinogenic results.” The FDA found that the evidence was insufficient and not conclusive. in 2009, the FDA assessed additional health claim qualifiers related to selenium. They rejected claims for a variety of types of cancer but permitted the health claim to be qualified for 3 kinds of cancer. The agency noted that the FDA finds it “highly doubtful” that selenium supplements lower the risks of developing bladder cancer among women or the risk of developing thyroid cancer. FDA also concluded that it is “highly likely” that supplements containing selenium reduce the chance of developing prostate cancer.

Further research is required to understand the full extent of the relationship between selenium levels and cancer risk and to determine if selenium supplements could help in preventing any cancer.

Cardiovascular disease

Selenoproteins reduce inflammation and also prevent platelet aggregation and lipid oxidation. Because of this, scientists have speculated that supplements with selenium could lower the risk of suffering from cardiovascular disease and deaths related to heart disease.

Early observational studies suggested that low selenium levels could raise the likelihood of developing cardiovascular disease. A meta-analysis in 2006 of 25 observational studies, mainly among men over 40, showed an inverted relationship between selenium levels and cardiovascular risk. Selenium levels in the blood ranged between 5.18 to 13.07 mcg/dL. Those who had the highest levels of selenium had an increase of 15% in the risk of suffering from coronary heart diseases than men who had the lowest concentrations.

Since then, research on the role of selenium in the development of cardiovascular disease has revealed conflicting results. A study of 1,042 middle-aged White women and men (mean of 40.8 years) found that elevated levels of selenium in plasma (mean 12.4 milligrams/dL) were linked to greater levels of total and non-high-density lipoprotein (HDL) cholesterol concentrations. On the other hand, studies of 13,887 adults within the United States showed no association between serum selenium levels in the beginning (mean 12.56 milligrams/dL) and the rate of cardiovascular death after 12 years of follow-up. In addition, an 18-year study conducted in a prospective cohort of 3,112 young adult males and women (age 20-32 years at the time of baseline) found no correlation between the baseline levels of toenail selenium as well as changes to carotid intima-media thickness or coronary artery calcium scores at the conclusion in the course of study.

Several clinical studies have investigated whether supplementation with selenium alone or as a part of a multivitamin/mineral supplement reduces the risk of heart disease. In one study, four healthy adults aged 60-74 had an average baseline concentration of plasma selenium of 9.12 mg/dL, 100, 200, 300, or 100 mg/day of selenium as yeasts or placebos for six months. Selenium supplements containing 100 and 200 mg/day reduced the total cholesterol in plasma by a mean of 8.5 as well as 9.7 mg/dL, and cholesterol that is not HDL to 7.7 or 10.4 mg/dL, respectively, and 300 mg/day selenium raised HDL concentrations in the range of 2.3 mg/dL. The study's authors stated that these findings' clinical significance is unclear. Similar studies have shown that supplementation with selenium on its own (100, 200, 300, or 300 mg/day) and supplementation using a multivitamin/mineral item with selenium (100 mg/day) is not a way to lower the risk of developing cardiovascular diseases or death from cardiac.

It was the SELECT study (detailed further in the Cancer section above) that examined the risk of cardiovascular disease as a secondary outcome in healthy men 17,488 and found no impact of 200 mg/day selenium on the risks of heart attack and stroke between 7 and 12 years old, in comparison to placebo. A Cochrane Review of SELECT and 11 other smaller randomized studies provided 100-800 mcg/day of selenium for 2 weeks up to 12 years in 19,715 primarily male adults. Additionally, the study found that selenium supplements did not decrease your risk for fatal or other nonfatal heart attacks. All trials were deemed to be low risk of bias.

Studies suggest that taking selenium supplements doesn't reduce the risk of heart disease; the inclusion of selenium in antioxidant blends could lessen the chance of dying from cardiovascular disease. A systematic review and meta-analysis included 43 randomized studies in adult patients who used selenium supplements on their own or as a component of antioxidant formulas for at most 24 weeks (researchers identified antioxidant formulas as having at least two of the following elements: selenium, retinol, and beta-carotene Vitamin C zinc, vitamin E and copper). Selenium by itself, which provides 100 to 400 mg per day, or antioxidant formulas containing or without 50 to 200 mg selenium, did not cause mortality due to cardiovascular disease or heart disease compared to placebo. However, when antioxidant formulas were divided into selenium-containing and non-selenium, cardiovascular mortality decreased by 23% among those who took antioxidant formulas that contained selenium compared to those who took antioxidant formulas that didn't contain selenium.

Overall, evidence from clinical trials does not support the use of supplements with selenium in reducing the risk of developing heart disease, especially in healthy individuals who get enough selenium through food sources. Further clinical trials are required to determine the contribution of selenium derived from food or nutritional supplements to heart health.

Alzheimer's disease and cognitive decline

Selenoproteins are antioxidants with anti-inflammatory effects. Serum selenium concentrations decrease with advancing age. Additionally, chronic selenium deficiencies are associated with a decline in cognitive capacity. Because of this, research has suggested that intake of more selenium could decrease the chance of developing cognitive decline.

A review of the 2011-2014 NHANES data revealed that higher total blood selenium levels and higher intakes were linked to more excellent cognitive scores among older adults. However, the results of other studies that have observed subjects are mixed. A survey of 1,012 men and women from Italy (mean age of 75) found that lower plasma selenium concentrations were linked to subtle neurological impairments. The participants in the lowest quartile of selenium in plasma (less than 6.67 mg/dL) were less neuromotor efficient than those in the upper quarter (more than 8.23 mcg/dL). However, in a study of 154 healthy individuals in Australia (96 percent of women aged 71 and older), 85 percent had selenium-replete levels (average of 16.9 mcg/dL). There was no relationship between plasma selenium levels and cognitive performance.

Researchers have assessed the possibility that taking antioxidant supplements that contain selenium can reduce the chance of cognitive decline in older adults. An analysis post-hoc of the Supplementation of Vitamines and Mineraux Antioxidants (SU.VI.MAX) study involving 447 participants aged 45-60 in France observed that in comparison with those who consumed a daily supplement consisting of 100 mcg of selenium with 120 mg of ascorbic acid and 30 mg of vitamin E and 6 mg beta-carotene along with 20 mg zinc over 8 years showed better episodic memory as well as semantic fluency scores six years after stopping supplementation selenium's role in the observed effects of this study has not been determined.

The results of observational studies show that people suffering from Alzheimer's illness (AD) are less likely to have levels of blood selenium in comparison to healthier older adults who are cognitively healthy. It was the Prevention of Alzheimer's Disease with Vitamin E and Selenium (PREADVISE) trial was the first massive primary prevention trial that studied its effects on selenium (200 mg/day as selenium) along with Vitamin E (400 IIU/day) in 7,540 healthy cognitively people aged 60 years or older. However, over the 5.4 years of supplementation, the study found no differences in the prevalence of developing AD or dementia in those who took selenium and vitamin E by themselves or selenium and vitamin E when compared to placebo.

A comprehensive review of and a meta-analysis of eleven clinical trials assessed the effects of supplements containing selenium alone or with other nutrients in adults between 69 and 89 years old suffering from cognitive decline or AD. Supplements that contain organic and inorganic types of selenium were tested. These studies revealed that selenium supplements only in various dosages, as well as selenium and other nutritional supplements for 12 to 24 months, didn't improve the cognitive scores of test subjects.

Selenium might play a part in maintaining brain health. However, evidence from clinical trials does not support the benefits of supplementing with selenium in depleted people to reduce the chance of cognitive decline and dementia in elderly adults.

HIV infection

In adults and children suffering from HIV, selenium deficiency has been linked with a greater risk of mortality and morbidity. However, studies that examine whether supplementation with micronutrients, including selenium, influences the risk of HIV transmission or the outcome of disease for both adults and children have yielded mixed outcomes. A prospective study conducted in Thailand did not find any associations with selenium status among children suffering from HIV and the outcomes of treatment. The study involved the study of 141 girls and boys with HIV (median age 7.3 years) and 97 who were treated with antiretroviral therapy (ART) for a duration which lasted for 48 weeks. Selenium levels at baseline (all that were sufficient) did not show any correlation with treatment results.

Clinical studies have shown the benefits of supplementing with selenium are limited in boosting immune function among those suffering from HIV. A clinical study in Rwanda looked at the effects of selenium supplements on the number of CD4+ T-cells for 300 women and men who were aged 21 or older who had HIV. The participants were diagnosed with CD4+ T-cell numbers between 400 and 650 cells/mcL; therefore, they were not qualified for ART. They were given 200 mg of selenium daily and a placebo for 24 months. The trial showed that the average CD4+ T cell counts decreased in both treatment and placebo groups, but the depletion rate was 43.8 percent lower in the group taking selenium. Selenium supplementation, however, did not affect the composite measure of having a count of CD4+ lower than 350 cells/mcL or the beginning of treatment.

Selenium supplementation did not provide any benefits in a controlled, randomized study in Iran in which 146 males and women who were receiving ART for HIV (mean time of 38.6 years) consumed 50 mg/day zinc, 200 mg/day selenium, or placebo for 6 months. Researchers then followed participants for 3 months and found that selenium supplementation didn't increase CD4+ T-cell count.

There were two Cochrane Reviews also concluded that selenium supplements have very little, if any, benefits for those suffering from HIV. The first review looked at whether supplementation with micronutrients reduces the incidence of HIV infection among children. It included 3 clinical trials that administered 30 or 60 mcg/day of selenium as part of a multiple-micronutrient formulation in children with HIV who were living in South Africa or Uganda. The researchers concluded that there was no evidence to conclude whether selenium supplementation could be beneficial. In the same way, the authors of a subsequent Cochrane Review of 4 clinical studies in 1,187 people suffering from HIV concluded that 200 mg/day of selenium throughout 9 to 24 months could result in little or no impact in CD4+ T-cell count or the amount of viral load. The review also concluded that there was no evidence to establish whether supplementation with selenium can increase the risk of hospitalization in people who suffer from HIV.

Researchers have also investigated the extent to which blood selenium levels or selenium supplementation influences pregnancy outcomes for women suffering from HIV. Studies have shown correlations with low blood selenium levels and a higher risk of preterm birth. Additionally, they suggest that supplementing selenium may reduce the risk of preterm delivery. For instance, a cross-sectional study conducted in Nigeria of 113 women who were between the ages of 15 and 49 with HIV discovered that women with selenium deficiencies (defined to be blood selenium lower than 7 mg/dL) from 14 to 26 weeks gestation were eight times more likely be born preterm than those who had normal selenium levels. The people who had an insufficient CD4+ T-cell count had a higher likelihood of having a premature birth. In a clinical study in Nigeria, the researchers looked into whether selenium supplementation affected pregnancy outcomes and progression of disease in 90 women who were pregnant and suffering from HIV (mean of 29.7 years) between 14 and 27 weeks gestation. In this study, participants received 200 mg/day of selenium or placebo between enrollment and birth. The participants who were selenium-treated had the lowest risk of 68% of having a preterm baby over those who received a placebo, but the chance of low birth weight was not different in either group. Additionally, supplementation with selenium did not alter any levels of HIV disease markers (CD4+ T-cells and HIV load).

In general, the clinical evidence regarding the effect of selenium supplementation on the risk in HIV transmission or outcomes from disease isn't conclusive, however a limited evidence suggests that it could lower the risk of preterm birth among people suffering from HIV. Further research is required to determine if supplementation with selenium can benefit children and adults living with HIV.

Male fertility

Infertility is a public health issue that affects approximately 15 percent of the population of Earth. Studies have shown that eating an optimum diet can improve sperm quality. Certain nutrients, like selenium, could also contribute to the process, possibly because they can reduce the stress of oxidation associated with male infertility. Selenoprotein, a glutathione peroxidase, a phospholipid hydroperoxide, is an important structural part of mature male sperm. A five-year study of prospective studies in Idiopathic male infertiles observed that both high and low selenium semen concentrations were linked to male infertility as well as reproductive failures.

Clinical trials investigating the effects of selenium supplementation on sperm quality have produced inconsistent results. A study in healthy males (nonsmokers) aged 18 to 45 was conducted with 300 mg/day of selenium (as selenium yeast) or a placebo for 48 weeks. No difference in sperm count or motility was observed in the two groups, and the semen volume decreased.

Contrarily, a three-month study conducted in Scotland with 69 males (mean age of 33 years) with lower sperm motility and reduced selenium levels in plasma (mean 8.1 Mcg/dL) discovered that 100 mg/day selenium supplemented with selenomethionine increased the levels of selenium in plasma as well as sperm motility and chances of conception when compared to placebo. There were no additional benefits if the vitamins A, C, and E were included in the supplement with selenium. Another three-month study that gave 200 mg of selenium per day as selenium yeast, or 200 mg daily coenzyme Q10 to 70 males (average age of 25 years) who suffered from idiopathic infertility, observed increases in sperm total and progressive mobility in men who were taking selenium. But, the trial did not have a control group, nor did it measure selenium levels at the baseline.

Further research is required to determine whether supplements with selenium can affect male fertility.

Thyroid disease

Selenium levels are more abundant within the thyroid gland than in other body organs. Similarly to the iodine mineral, it has significant functions in thyroid hormone production and metabolism. Selenoproteins, for instance, play a key role in converting prohormone T4 to active T3. Additionally, selenoproteins glutathione peroxidase, as well as the reductase, protect the thyroid gland with hydrogen peroxide generated in the process of synthesizing thyroid hormone.

Research on epidemiology has found links between low selenium levels and an increased risk of developing thyroid diseases. However, this association was observed only for women. As an example, the data of 1,900 middle-aged women and men with mean serum selenium levels of 12.4 milligrams/dL found an inverted correlation between serum selenium levels and thyroid volume and an effect of selenium to protect against the risk of goiter in women who participated however not in the men. A cross-sectional study of 805 women aged 18 to 65 and 60-65 years old in Denmark with average serum selenium levels of 9.7 milligrams/dL and slight Iodine deficiencies also revealed an inverted relationship between selenium levels in the blood and thyroid volume for women but not in the men.

A controlled trial conducted a randomized trial that administered 100, 300, 200, and 100 mcg/day of selenium as selenium yeast for six months in 368 healthy males and women aged 60 to age 74, having mean levels in the range of 9.13 mcg/dL. The study found no impact on thyroid functions even though serum selenium levels were higher in all three groups.

Chronic autoimmune thyroiditis (AIT) which is also known as Hashimoto's thyroiditis affects 1 or 2 percent population, mainly females in middle age. Numerous clinical trials have examined the effects of supplementing with selenium on thyroid antibodies in patients suffering from AIT. An extensive review of meta-analyses and systematic reviews of 16 studies examined the effect of selenium supplementation on the serum thyroid peroxidase antibodies (TPOAb) as well as thyroglobulin antibodies (TgAb) amounts in people who suffer from AIT who received levothyroxine treatment compared with those who were newly diagnosed and not being treated with levothyroxine. The study included 1,494 adults (mainly females) who received up to 200 mg/day of selenium (as sodium selenite or selenomethionine) for three to twelve months, and most trials were controlled by placebo. Five trials reported baseline selenium levels ranging between 3.7 to 8.5 milligrams/dL, indicating inadequate marginal selenium levels in several participants. The other trials didn't report the selenium levels at baseline. In the levothyroxine-treated groups, selenium supplementation lowered TPOAb levels. Furthermore, selenomethionine was more efficient than sodium selenite in decreasing TPOAb, possibly due to more excellent absorption. In the levothyroxine-untreated groups of newly diagnosed participants, selenium supplementation lowered TPOAb and TgAb levels in the 3-month studies but not in the 6- or 12-month studies.

Several other studies have examined the effects of supplementation with selenium on thyroid function and the quality of life in people with AIT. A systematic review contained 9 controlled studies (all included in the review of 16 studies mentioned above) of 679 women (mean age range 39-48 years). A few trials included levothyroxine however the studies were restricted to those that used selenium as the sole ingredient. Results indicated that selenium supplementation that ranged from 80-200 mg/day in the form of selenomethionine and sodium selenite over 3-12 months did not alter TSH levels and thyroid echogenicity (ultrasound is a marker of hypothyroidism) or the health-related quality of living. In the study mentioned above, the participants were deficient to minor selenium levels on seven occasions in the 9 studies that examined the condition. The researchers found that the evidence does not support the usage of selenium supplements for AIT.

As high as 50% of pregnant women with TPOAb or TgAb positive during the first trimester will experience postpartum thyroiditis. Twenty percent to 40 percent of these women will suffer from permanent hypothyroidism. But, the results from clinical studies examined the effects of supplementing selenium for this group. In one study in one study, 151 pregnant White women aged between 18 and 36 years old who were positive for TPOAb, had healthy thyroid functions and low selenium levels (mean 8.09 mg/dL), consumed 200 mg of selenium daily in the form of selenomethionine or placebo for 12.5 weeks of gestation to 12 months after the birth. In the selenium group, 28.6 percent had postpartum thyroid problems compared with 48.6 percent of the participants of the group with placebo. Furthermore, 11.7% of participants in the selenium group suffered from permanent hypothyroidism as compared to 20.3 percent in the group with a placebo. Another study provided 83 mg/day of selenium in the form of selenomethionine for 45 women in the womb who were TPOAb or TgAb positive. It also reported a reduction in these antibodies six months postpartum, compared to placebo. A study that gave 60 mg of selenium daily to selenium yeast TPOAb-positive women during pregnancy who were moderate to mildly deficient in iodine showed no change in TPOAb levels after delivery.

In 2017, The American Thyroid Association issued a moderate recommendation for the supplementation of selenium for pregnant women who are TPOAb positive based on moderate quality evidence.

Although selenium can be involved in normal thyroid function, more research is necessary to determine the significance of selenium supplements in thyroid diseases, specifically based on age and gender.

Health Risks of Excessive Selenium from Excessive Selenium

Consumption of a steady amount of organic and inorganic selenium can have similar results. Early signs of an excessive intake include a garlic smell in the breath and a metallic taste inside the mouth. The most frequent clinical symptoms of a long-term high intake of selenium or selenosis are loss of hair and nail loss or brittleness. Other symptoms and signs include a rash on the skin, nausea, fatigue, diarrhea, irritability, and neurological system issues.

As mentioned earlier, Brazil nuts contain huge levels of selenium (68-91 mg per nut) and may cause selenium poisoning when consumed frequently. Selenium-related toxicity in the acute form has been reported from the ingestion of unformulated prescription drugs that contain large quantities of selenium. For instance, in 2008, 201 people suffered extreme adverse reactions as a result of drinking a dietary supplement that contained 200 times the stated amounts of selenium. Selenium poisoning can lead to severe neurological and digestive symptoms such as severe respiratory distress syndrome, myocardial infarction, muscle tenderness, hair loss as well as lightheadedness, tremors and facial flushing, heart failure, kidney failure, and, in some cases, even death.

The FNB has set the ULs for selenium in supplements and food by the amount of selenium associated with nail brittleness, hair, and loss. These ULs do not apply to individuals taking selenium as a result of the care of a doctor.

In 2023 2023 2023, the Panel on Nutrition, Novel Foods and Food Allergens of the European Food Safety Authority released an opinion based on science regarding the ULs on selenium. The decision was based on systematic studies that looked at the relationship between excessive intake of selenium and the clinical effects, including hair loss; the panel decided to set an upper limit of selenium that is 255 mg/day to all adult individuals, which includes those who are lactating or pregnant and lower levels that range from 70 to 300 mg/day for adolescents and children, based on the age.

Interactions between Medications and Medications

Selenium is known to interact with certain medications, and some medications could affect selenium levels. An example is listed below. People who take this and other medicines regularly should discuss their selenium levels with their healthcare providers.


Cisplatin is an inorganic platinum-based chemotherapy drug that can be utilized to treat bladder, ovarian, and lung cancers. Cisplatin may reduce the levels of selenium in serum and hair, but whether the reductions impact clinical outcomes is not yet known. A few small studies have demonstrated that selenium supplementation may reduce the toxic effects of cisplatin. However, the researchers of the Cochrane Review concluded that the evidence that suggests that selenium supplementation can reduce the adverse effects of chemotherapy is insufficient.

Selenium and Healthful Diets

The 2020-2025 Guidelines for Dietary Guidelines for Americans stipulates that “Because food products provide a wide range of nutrients as well as other components that are beneficial for well-being, nutritional needs must be fulfilled primarily through food. … For certain instances, fortified food items and supplements to diets are beneficial when it's not feasible to satisfy the needs of some or all nutrients (e.g., for specific phases of life like pregnant).”

For more information on creating an appropriate diet plan, see the Dietary Guidelines for Americans and the USDA's MyPlate.

Dietary Guidelines for Americans Dietary guidelines describe the ideal diet for healthy people.

  • Included are a variety of fruits and vegetables, grains (at least half whole grains), low-fat, fat-free, and fat-free milk, yogurt, cheese, and oils.
    • Selenium is rich in a wide variety of whole grains and dairy products, such as yogurt and milk. Certain ready-to-eat breakfast cereals and certain fruits and veggies also contain it.
  • It includes a range of protein-rich foods, such as lean meats, poultry, eggs, seafood, beans, peas, lentils, seeds, nuts, and soy products.
    • Pork, turkey, beef, chicken, fish, eggs, and shellfish all have high levels of selenium. Brazil nuts are particularly rich in selenium.
  • Limits the consumption of foods and drinks high in sugars, added sugars, saturated fats, and sodium.
  • The law prohibits the consumption of alcoholic beverages.
  • Keeps you within your daily calorie requirements.
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