Selenium
Research reviewed: Up until 03/2026
Selenium is a dietary supplement with 10 published peer-reviewed studies involving 1,824 participants, researched for Antioxidant, Hair and Nails, Immunity and 1 more areas.
Evidence at a Glance
Strength is scored by study design, sample size, study type, and outcomes
Antioxidant
ModerateHair and Nails
ModerateImmunity
StrongSpermatogenesis
StrongResearch Visualised
Visual breakdown of the clinical data.
Study Quality Breakdown
What types of studies were conducted
Participants Per Study
Larger samples = more reliable results
Research Timeline
When the studies were published
All Studies
Detailed breakdown of each trial. Click to expand.
Antioxidant
To evaluate whether selenium supplementation can increase the activity of glutathione peroxidase 1 (GPx-1), a key antioxidant enzyme that protects the heart and blood vessels from oxidative damage, in patients with coronary artery disease (CAD) who have impaired blood vessel function. GPx-1 is like a 'cleanup crew' inside cells that neutralises harmful molecules (free radicals) before they can damage tissues, especially in the heart and blood vessels.
Study Type
Randomised, double-blind, placebo-controlled, phase II clinical trial
Purpose
To evaluate whether selenium supplementation can increase the activity of glutathione peroxidase 1 (GPx-1), a key antioxidant enzyme that protects the heart and blood vessels from oxidative damage, in patients with coronary artery disease (CAD) who have impaired blood vessel function. GPx-1 is like a 'cleanup crew' inside cells that neutralises harmful molecules (free radicals) before they can damage tissues, especially in the heart and blood vessels.
Dose
200 µg/day or 500 µg/day sodium selenite, or matching placebo. Sodium selenite is a synthetic, inorganic compound used to deliver selenium.
Participants
433 male and female patients with stable coronary artery disease (CAD) with impaired blood vessel function
Duration
12 weeks
Results
The researchers observed that at 200 µg, GPx-1 activity increased from 37.0 to 41.1 U/gHb, while at the higher dose of 500 µg, it increased from 38.1 to 42.6 U/gHb, showing that a larger dose produced a greater increase in enzyme activity.
To investigate the effects of selenium supplementation on oxidative stress biomarkers in patients with migraine, a condition associated with significantly elevated oxidative damage markers, including raised MDA (lipid oxidation) and depleted antioxidant capacity (TAC).
Study Type
Randomised, double-blind, placebo-controlled trial
Purpose
To investigate the effects of selenium supplementation on oxidative stress biomarkers in patients with migraine, a condition associated with significantly elevated oxidative damage markers, including raised MDA (lipid oxidation) and depleted antioxidant capacity (TAC).
Dose
200 µg/day selenomethionine (a readily absorbed organic selenium form), or placebo
Participants
72 patients with migraine
Duration
12 weeks
Results
The researchers observed that selenium supplementation significantly reduced plasma MDA levels (a direct marker of oxidative damage to cell membrane lipids) compared to placebo (0.34 vs. 1.83 nmol/mL). Total antioxidant capacity (measuring the blood's ability to neutralise free radicals and protect DNA, proteins, and fats from oxidative damage) significantly increased in the selenium group. Total oxidative status a measure of how much oxidative stress is present in the blood) was also significantly reduced. Overall, selenium supplementation appears to effectively reduce oxidative stress and enhance the body’s antioxidant defenses.
Hair and Nails
To evaluate the effects of a multi-ingredient oral supplement — containing hydrolysed fish-origin collagen, amino acids (taurine, cysteine, methionine), iron, and selenium — in subjects with hair loss (androgenetic alopecia/FAGA or chronic telogen effluvium) when combined with standard hair-loss drug treatments versus drug treatment alone.
Study Type
Prospective, randomised, assessor-blinded, controlled trial
Purpose
To evaluate the effects of a multi-ingredient oral supplement — containing hydrolysed fish-origin collagen, amino acids (taurine, cysteine, methionine), iron, and selenium — in subjects with hair loss (androgenetic alopecia/FAGA or chronic telogen effluvium) when combined with standard hair-loss drug treatments versus drug treatment alone.
Dose
Group A: Oral supplement containing selenium (amount not individually specified) + hydrolysed collagen, taurine, cysteine, methionine, iron in addition to a specific drug treatment decided by the investigator according to the type of hair loss (AGA/FAGA or TE) Group B: Specific drugs treatment only (control)
Participants
83 subjects (average age 41 years; 26 men, 57 women) with androgenetic alopecia (59 subjects) or chronic telogen effluvium (24 subjects)
Duration
12 weeks
Results
At 12 weeks, the supplement group showed a significantly better Global Assessment Score (GAS) — a standardised 7-point clinical photograph scoring scale measuring visible hair improvement — compared to drug treatment alone. The GAS score is assessed by a blinded investigator from standardised photographs; a positive score means hair is visibly improved.
Immunity
To examine the effect of dietary selenium supplementation on two key branches of immune cell function: (1) cytotoxic lymphocytes — immune cells that recognise and kill abnormal or infected cells; and (2) natural killer (NK) cells — immune cells that provide rapid defence against virally infected and cancerous cells, without needing prior exposure to the threat.
Study Type
Randomised, placebo-controlled trial
Purpose
To examine the effect of dietary selenium supplementation on two key branches of immune cell function: (1) cytotoxic lymphocytes — immune cells that recognise and kill abnormal or infected cells; and (2) natural killer (NK) cells — immune cells that provide rapid defence against virally infected and cancerous cells, without needing prior exposure to the threat.
Dose
200 µg/day selenium (as sodium selenite), or placebo
Participants
32 male and female healthy volunteers aged 23-40 years
Duration
8 weeks
Results
Researchers observed that selenium supplementation for 8 weeks resulted in a 118% significant increase in cytotoxic lymphocyte-mediated tumour cytotoxicity (this means immune cells became more than twice as effective at identifying and killing abnormal or tumour cells) compared to baseline (the participants’ measurements before starting supplementation). Natural killer (NK) cell activity, which are the body’s first-line defense cells against viruses and cancer, also significantly increased by 82.3% compared to baseline. These improvements were also significantly greater than those seen in the placebo group.
To examine whether selenium supplementation can slow the progression of HIV disease by preserving the immune system , specifically by reducing the rate of decline in CD4+ T-cell count (the main immune cells targeted and destroyed by HIV, and their count determines disease progression and when antiretroviral therapy should begin).
Study Type
Multi-centre, double-blind, placebo-controlled, randomised clinical trial
Purpose
To examine whether selenium supplementation can slow the progression of HIV disease by preserving the immune system , specifically by reducing the rate of decline in CD4+ T-cell count (the main immune cells targeted and destroyed by HIV, and their count determines disease progression and when antiretroviral therapy should begin).
Dose
200 µg/day selenium (one tablet daily), or identical placebo
Participants
300 HIV-infected men and women in Rwanda who were ART-naive (not yet on antiretroviral therapy), aged 21 years and above
Duration
24 months (2 years) with assessments every 6 months
Results
Researchers observed that the rate of CD4+ T-cell decline (key immune cells that fight infections) was significantly reduced by 43.8% in the selenium group. This shows that selenium supplementation slowed the immune decline caused by HIV nearly in half, and that the body's key immune defence cells were preserved significantly longer in those taking selenium.
To evaluate the effects of selenium supplementation on immune cell populations — including T-cell subsets (CD4+ T-helper cells and CD8+ cytotoxic T cells) and natural killer (NK) cells — in healthy elderly adults, a population known to experience declining immune function with age (immunosenescence).
Study Type
Prospective, randomised, placebo-controlled trial
Purpose
To evaluate the effects of selenium supplementation on immune cell populations — including T-cell subsets (CD4+ T-helper cells and CD8+ cytotoxic T cells) and natural killer (NK) cells — in healthy elderly adults, a population known to experience declining immune function with age (immunosenescence).
Dose
400 µg/day selenium, or beta-carotene (45 mg/day), or selenium + beta-carotene combination, or placebo
Participants
Free-living healthy elderly adults aged 57–84 years
Duration
6 months supplementation, then 2 months follow-up after discontinuation
Results
Researchers observed that selenium supplementation significantly increased total T-cell count by 27%. Participants also demonstrated a 65% significantly higher level of T lymphocytes (a type of immune cell) compared to the placebo group. This increase was mainly due to higher levels of CD4+ T-helper cells, which are the “command cells” that help organize and direct the body’s immune response against infections. Researchers also observed that NK cell cytotoxicity (the ability of natural killer cells to kill infected or abnormal cells) significantly increased with selenium supplementation. Overall, these findings suggest that selenium supplementation may help enhance both immune coordination and immune defense mechanisms, particularly in older adults, making it a potentially beneficial support for maintaining immune function.
Spermatogenesis
To determine whether the decline in selenium intake in Scottish men might contribute to male subfertility, specifically by examining whether selenium supplementation can improve sperm motility and conception rates in men with reduced sperm motility. Sperm motility is the ability of sperm to move efficiently, which is essential for successful fertilization as sperm must travel through the female reproductive tract to reach and fertilize the egg.
Study Type
Randomised, double-blind, placebo-controlled, phase II clinical trial
Purpose
To determine whether the decline in selenium intake in Scottish men might contribute to male subfertility, specifically by examining whether selenium supplementation can improve sperm motility and conception rates in men with reduced sperm motility. Sperm motility is the ability of sperm to move efficiently, which is essential for successful fertilization as sperm must travel through the female reproductive tract to reach and fertilize the egg.
Dose
100 µg/day L-selenomethionine or selenium combined with 1 mg vitamin A, 10 mg vitamin C, and 15 mg vitamin E or placebo
Participants
69 men with reduced sperm motility (64 completed with an average age of 33 years)
Duration
3 months
Results
Sperm motility significantly improved in both selenium-treated groups compared to placebo. Sperm density was unaffected. Additionally, 11% of men in the selenium treatment groups (5 out of 46 treated men) achieved paternity — meaning their partner became pregnant — during the course of the study, while none in the placebo group achieved paternity.
To assess whether selenium–vitamin E combination therapy can improve semen quality and achieve spontaneous pregnancy in infertile men diagnosed with asthenospermia (poor sperm motility) or asthenoteratospermia (poor sperm motility and shape).
Study Type
Open-label, single-arm interventional study (uncontrolled)
Purpose
To assess whether selenium–vitamin E combination therapy can improve semen quality and achieve spontaneous pregnancy in infertile men diagnosed with asthenospermia (poor sperm motility) or asthenoteratospermia (poor sperm motility and shape).
Dose
200 µg/day selenium + 400 IU/day vitamin E for 14 weeks (no placebo group — all participants received treatment)
Participants
690 infertile men diagnosed with asthenospermia or asthenoteratospermia (semen analysis abnormalities without a known cause)
Duration
14 weeks
Results
A significant total improvement in sperm motility, morphology, or both was observed in 52.6% of participants (362 out of 690 cases). Spontaneous pregnancy (conception without IVF) occurred in 10.8% of cases (75 out of 690). No response to treatment occurred in 253 cases (36.6%) after 14 weeks of combination therapy. The results suggest that supplemental selenium and vitamin E may improve semen quality and have beneficial and protective effects, especially on sperm motility.
Researchers aimed to explore the effect of selenium therapy on semen parameters, antioxidant capacity, and sperm DNA fragmentation (SDF) in infertile men diagnosed with idiopathic oligoasthenoteratospermia (OAT; unexplained infertility).
Study Type
Prospective clinical study
Purpose
Researchers aimed to explore the effect of selenium therapy on semen parameters, antioxidant capacity, and sperm DNA fragmentation (SDF) in infertile men diagnosed with idiopathic oligoasthenoteratospermia (OAT; unexplained infertility).
Dose
200 µg/day selenium
Participants
65 infertile men with idiopathic oligo-asthenoteratospermia and 55 fertile controls
Duration
6 months
Results
Researchers observed that after 6 months of selenium supplementation , men with unexplained infertility (called idiopathic OAT, meaning low sperm count, poor movement, and abnormal shape with no known cause) showed significant improvements in sperm quality. Sperm concentration (number of sperm), progressive motility (how well sperm move forward), and total motility (overall movement) all significantly improved. Participants demonstrated increased antioxidant capacity (the body’s ability to protect sperm from damage caused by harmful molecules called free radicals), including significantly higher levels of TAC (total antioxidant capacity) and CAT (catalase, an enzyme that helps break down harmful substances). Researchers also observed a significant decrease in sperm DNA fragmentation (SDF), meaning damage to the sperm’s genetic material, which is important because less DNA damage improves fertility potential. Importantly, the study found a negative association between SDF and sperm movement, where higher DNA damage was associated with poorer motility. Overall, the study suggests that selenium may be a useful supportive treatment to improve fertility outcomes in these men.
To assess the effect of selenium therapy on semen parameters in infertile men with or without varicocele, a condition where the veins inside the scrotum (the pampiniform plexus) become enlarged, similar to varicose veins in the legs.
Study Type
Prospective clinical study
Purpose
To assess the effect of selenium therapy on semen parameters in infertile men with or without varicocele, a condition where the veins inside the scrotum (the pampiniform plexus) become enlarged, similar to varicose veins in the legs.
Dose
200 µg/day selenium
Participants
80 infertile men with an average age of 33 years
Duration
3 months
Results
After three months of daily oral selenium treatment (200 µg/day), both groups of infertile men, those with varicocele and those without, experienced significant increases in progressive and total sperm motility (crucial for traveling through the female reproductive tract to fertilize an egg). Specifically, infertile men with varicocele saw a 32.7% significant increase in progressive motility and a 23.6% significant increase in total motility, which was a higher improvement compared to infertile men without varicocele, who experienced a 24.1% significant increase in progressive motility and a 12.6% significant increase in total motility. While sperm concentration and normal sperm morphology did not show significant changes, these findings suggest that selenium could be a valuable adjunctive treatment for male infertility, especially when associated with varicocele.
Frequently Asked Questions
Common questions about Selenium research
There are currently 10 peer-reviewed studies on Selenium (Selenium), involving 1,824 total participants. Research covers Antioxidant, Hair and Nails, Immunity and 1 more areas. The overall evidence strength is rated as Very Strong.
The evidence is currently rated as "Very Strong Evidence". This rating is based on study design quality (randomisation, blinding, placebo controls), sample sizes, study types (10 human studies), and reported outcomes.
Selenium has been researched for: Antioxidant, Hair and Nails, Immunity, Spermatogenesis. Each area has its own body of evidence which you can explore in the study breakdowns above.
Yes, 10 out of 10 studies are human trials. Human trials carry more weight in our evidence scoring system.
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