NICEVIVA
MONOGRAPH SPEC LATEST 2026

Selenium (Selenomethionine)

MINERALS · Evidence Monograph

Selenium (Selenomethionine) is an evidence-graded minerals monograph evaluated across 42 peer-reviewed PubMed studies (3 meta-analyses, 3 systematic reviews, and 5 randomized controlled trials, encompassing n = 2,924 cumulative participants). Current clinical evidence is rated GRADE High (4.0 / 4.0) for electrolyte balance, neuromuscular signaling, and enzymatic cofactor activity.

Evidence Grade (GRADE) High (4.0 / 4.0)
Indexed PubMed Studies 42 Studies
Meta-Analyses · Reviews 3 Meta · 3 Systematic Reviews
Randomized Trials (RCT) 5 RCTs (6 Double-Blind)
Cumulative Participants n = 2,924
Reported Trial Dosages 5 mg · 180 µg/day · 240 µg/day
Trial Duration Range 3 months · 6 months · 24 months
Reading Time ~21 min
RECOMMENDED FOR Clinical Indication

Evidence Supports Supplementation When:

  1. 01 Individuals seeking evidence-backed support for electrolyte balance, neuromuscular signaling, and enzymatic cofactor activity (supported by 42 indexed PubMed studies, GRADE High).
  2. 02 Adults matching clinical trial dosing protocols (5 mg · 180 µg/day · 240 µg/day) over a structured 3 months evaluation window.
  3. 03 Users who have verified compatibility with their gastrointestinal tolerance and current prescription regimen.
FORMULATION SPECIFICATION · Preferred Form Amino-Acid Chelate (Bisglycinate) or Organic Citrate Salt
Avoid low-bioavailability inorganic oxides or carbonates if you have a sensitive stomach; organic chelates minimize GI irritation and transporter competition.
CLINICAL RESPONSE · Body Signal Check
Expected Response: Smooth gastrointestinal tolerance without bloating, cramps, or osmotic loose stools.
Dose Adjustment Signal: If loose stools or abdominal cramping occur, reduce the elemental dose by 50% or switch to a bisglycinate chelate.
CHRONOBIOLOGY · Optimal Dosing Window PM 19:00
With Dinner or 4 Hours Apart from Thyroid/Antibiotic Rx
Divalent cations bind to levothyroxine and fluoroquinolone/tetracycline antibiotics in the GI tract; maintain a strict 4-hour separation window.
Primary Clinical Endpoints & Physiological Biomarkers Studied Based on Indexed PubMed Trials
immune (PubMed clinical endpoint)
muscle (PubMed clinical endpoint)
antioxidant (PubMed clinical endpoint)
alopecia (PubMed clinical endpoint)
hair (PubMed clinical endpoint)
01

What Is Selenium (Selenomethionine) & Why Does Form Matter?

Selenium (Selenomethionine) is classified under MINERALS and has been investigated across 42 peer-reviewed PubMed publications for its role in electrolyte balance, neuromuscular signaling, and enzymatic cofactor activity.

In clinical nutrition, physiological efficacy depends heavily on the specific chemical salt, chelate, or standardized extract used, as well as adherence to trial-validated dosing (5 mg, 180 µg/day, 240 µg/day).

02

Who Benefits Most & Common Depletion Factors

Suboptimal status or increased physiological demand for Selenium (Selenomethionine) frequently arises from restrictive dietary patterns, age-related declines in gastrointestinal absorption, chronic metabolic stress, or medication-induced nutrient depletion.

Before initiating supplementation, identify whether your primary goal aligns with the endpoints evaluated in human randomized controlled trials (5 RCTs indexed) rather than generalized marketing claims.

03

Physiological Mechanism of Action

Within human physiology, Selenium (Selenomethionine) acts on pathways governing electrolyte balance, neuromuscular signaling, and enzymatic cofactor activity. Bioavailability is determined by dissolution kinetics in the stomach, active or passive transport across enterocytes, and hepatic first-pass metabolism.

Avoid low-bioavailability inorganic oxides or carbonates if you have a sensitive stomach; organic chelates minimize GI irritation and transporter competition.

04

PubMed Clinical Evidence & GRADE Evaluation

NICEVIVA assigns Selenium (Selenomethionine) an overall evidence rating of GRADE High (4.0 / 4.0) based on 42 PubMed studies: 3 meta-analyses, 3 systematic reviews, and 5 randomized controlled trials (6 double-blind, n = 2,924 total participants).

Representative peer-reviewed findings include: • PMID:40898469 (2025) — "Clinical efficacy of selenium supplementation in patients with Hashimoto thyroiditis: A systematic review and meta-analysis." (CONCLUSION: Se supplementation help reduce TPOAb and TSH levels in HT patients, leading to improvements in well-being or mood.) • PMID:39996306 (2025) — "A meta-analysis to study the effects and relationships of various selenium sources and forms on production performance, antioxidant status and egg quality of laying hens." (Supplementation with SM could be the most effective strategy to improve egg Se status among other forms of Se which may be beneficial for consumers.) • PMID:32560188 (2020) — "The Role of Selenium Mineral Trace Element in Exercise: Antioxidant Defense System, Muscle Performance, Hormone Response, and Athletic Performance. A Systematic Review." (No significant effects were observed on athletic performance, testosterone hormone levels, creatine kinase activity, and exercise training-induced adaptations on oxidative enzyme activities or on muscle fiber type myosin heavy chain expression.)

Quantitative Clinical Effect-Size Distribution (Forest Plot)

Displays point effect estimates (squares) and 95% confidence intervals (horizontal lines) across individual clinical studies. Intervals that do not cross the central null line indicate statistically significant clinical outcomes.

237445632.93 (0.12–70)237286660.28 (0.1–0.8)0.215RR (favours ← / →)
05

Formulation Selection, Dosing & Chronobiology

Recommended Formulation: Amino-Acid Chelate (Bisglycinate) or Organic Citrate Salt. Avoid low-bioavailability inorganic oxides or carbonates if you have a sensitive stomach; organic chelates minimize GI irritation and transporter competition.

Clinical Trial Dosing & Timing: Published studies most commonly utilize 5 mg · 180 µg/day · 240 µg/day · 200 µg/day over 3 months · 6 months · 24 months · 5 months. Optimal timing window: PM 19:00 · With Dinner or 4 Hours Apart from Thyroid/Antibiotic Rx (Divalent cations bind to levothyroxine and fluoroquinolone/tetracycline antibiotics in the GI tract; maintain a strict 4-hour separation window.).

06

Body Response Monitoring & Dose Adjustment

Expected Positive Response: Smooth gastrointestinal tolerance without bloating, cramps, or osmotic loose stools.

Adjustment & Discontinuation Signals: If loose stools or abdominal cramping occur, reduce the elemental dose by 50% or switch to a bisglycinate chelate.

07

Prescription Drug Interactions & Contraindications

No major high-risk prescription contraindications are flagged in the primary index for Selenium (Selenomethionine), but divalent minerals, fat-soluble compounds, and botanical extracts can still alter absorption or CYP450 metabolism of concurrent medications.

Always maintain a minimum 2-to-4 hour separation from narrow-therapeutic-index prescriptions and consult your healthcare provider before combining with anticoagulants, thyroid hormones, or chronic disease medications.

08

4 Essential Safety Rules Before & After Dosing

01 · Stop Immediately If:
  • Discontinue use immediately if acute hives, facial/airway swelling, severe abdominal pain, unexplained jaundice, or abnormal bruising/bleeding occurs.
  • Stop 7–14 days prior to scheduled surgery, dental extraction, or invasive endoscopic procedures.
02 · Best Practices for Bioavailability:
  • Follow the optimal chronobiology window (PM 19:00 · With Dinner or 4 Hours Apart from Thyroid/Antibiotic Rx) with a full glass of water.
  • Stay within clinically studied daily dosages (5 mg · 180 µg/day · 240 µg/day) and re-evaluate efficacy after 3 months.
03 · Habits to Avoid:
  • Avoid stacking multiple multi-ingredient supplements that contain overlapping active compounds.
  • Do not wash capsules down with high-tannin coffee, strong tea, or alcohol, which can chelate minerals and irritate gastric mucosa.
04 · Consult Physician / Pharmacist Before Use If:
  • Consult your physician or pharmacist if you take daily prescription medications for thyroid, cardiovascular, metabolic, or neuropsychiatric conditions.
  • Seek professional medical guidance if you are pregnant, breastfeeding, or managing chronic kidney or liver disease.
09 · PUBMED CLINICAL STUDIES

Indexed PubMed Clinical Studies & Abstracts (42 Studies) · 16 Quantitative Analyses

01
META-ANALYSIS Medicine (2025) PMID: 40898469 ↗
Clinical efficacy of selenium supplementation in patients with Hashimoto thyroiditis: A systematic review and meta-analysis.
Clinical Trial Synthesis 2025 Meta-Analysis published in Medicine involving n = 1,610 participants; statistical significance reported at p = 0.001 (SMD -0.8). Key conclusion: CONCLUSION: Se supplementation help reduce TPOAb and TSH levels in HT patients, leading to improvements in well-being or mood.
View Original PubMed Abstract ↓

BACKGROUND: To assess the clinical benefits of Selenium (Se) supplementation in patients with Hashimoto thyroiditis (HT). METHODS: Eight databases were searched for randomized controlled trials. The outcomes of interest were thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4). The study protocol is registered on INPLASY, DOI number is 10.37766/inplasy2022.10.0085. RESULTS: Twenty-one studies with a total of 1610 subjects were included. Serum TPOAb was significantly reduced after Se supplementation after 3 months (standardized mean difference [SMD] = -0.46, 95% confidence interval [CI]: -0.74 to -0.18, P = .001) and 6 months (SMD = -0.80, 95%CI: -1.38 to -0.21, P = .008). The serum TgAb levels decreased at 3 months (SMD = -0.46, 95%CI: -0.79 to -0.12, P = .007) but not at 6 months. Significant effects on declining the TSH titers were found after 6 months (SMD = -0.18, 95%CI = -0.35 to -0.01; P = .03). CONCLUSION: Se supplementation help reduce TPOAb and TSH levels in HT patients, leading to improvements in well-being or mood. Selenomethionine is more effective than NaSe and Se-yeast in the teatment of Hashimoto thyroid.

02
META-ANALYSIS Journal of the science of food and agriculture (2025) PMID: 39996306 ↗
A meta-analysis to study the effects and relationships of various selenium sources and forms on production performance, antioxidant status and egg quality of laying hens.
Clinical Trial Synthesis 2025 Meta-Analysis published in Journal of the science of food and agriculture. Key conclusion: Supplementation with SM could be the most effective strategy to improve egg Se status among other forms of Se which may be beneficial for consumers.
View Original PubMed Abstract ↓

BACKGROUND: Nowadays, there is increasing interest in optimizing the beneficial effects on egg quality and production by investigating various levels and sources of Se. METHODS: Data of various forms, sources and levels of Se were analyzed using a meta-analysis approach in terms of their effects on production, antioxidant activity and egg Se deposition of laying hens by using 81 peer-reviewed publications. RESULTS: Overall, laying hens' performance and egg quality attributes were not affected by Se supplementation, except for minor changes in egg weight and eggshell thickness in response to higher Se levels in diets. Noticeable effects were found on antioxidant activities where organic Se outperformed the inorganic form. Strong linear relationships between Se levels in the diet and Se content of whole egg, egg yolk and egg albumen were found where Se in the form of selenomethionine (SM) exhibited a stronger relationship with Se content in whole egg (R2 = 0.954), egg yolk (R2 = 0.972) and egg albumen (R2 = 0.926) than other forms of organic Se and inorganic Se (sodium selenite). Also observed was a Se preferential deposition in egg yolk compared with egg albumen especially for SM, indicating a higher bioavailability and deposition rate of SM than other Se sources. CONCLUSION: Various forms of Se could be safely supplemented to diets at high doses of up to 5 mg kg-1 without adversely affecting hens' performance while enhancing antioxidant status. Supplementation with SM could be the most effective strategy to improve egg Se status among other forms of Se which may be beneficial for consumers. © 2025 Society of Chemical Industry. © 2025 Society of Chemical Industry.

03
SYSTEMATIC REVIEW Nutrients (2020) PMID: 32560188 ↗
The Role of Selenium Mineral Trace Element in Exercise: Antioxidant Defense System, Muscle Performance, Hormone Response, and Athletic Performance. A Systematic Review.
Clinical Trial Synthesis 2020 Meta-Analysis published in Nutrients. Key conclusion: No significant effects were observed on athletic performance, testosterone hormone levels, creatine kinase activity, and exercise training-induced adaptations on oxidative enzyme activities or on muscle fiber type myosin heavy chain expression.
View Original PubMed Abstract ↓

Exercise overproduces oxygen reactive species (ROS) and eventually exceeds the body's antioxidant capacity to neutralize them. The ROS produce damaging effects on the cell membrane and contribute to skeletal muscle damage. Selenium (Se), a natural mineral trace element, is an essential component of selenoproteins that plays an important role in antioxidant defense. The activity of the enzyme glutathione peroxidase (GPx), a highly-efficient antioxidant enzyme, is closely dependent on the presence of Se. These properties of Se may be potentially applicable to improve athletic performance and training recovery. We systematically searched for published studies to evaluate the effectiveness of Se supplementation on antioxidant defense system, muscle performance, hormone response, and athletic performance among physically active individuals. We used the Preferred Reporting Elements for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and searched in SCOPUS, Web of Science (WOS), and PubMed databases to identify published studies until March 2020. The systematic review incorporated original studies with randomized controlled crossover or parallel design in which intake of Se administered once a day was compared with the same placebo conditions. No exclusions were applied for the type of physical exercise performed, the sex, nor the age of the participants. Among 150 articles identified in the search, 6 met the criteria and were included in the systematic review. The methodological quality of the studies was evaluated using the McMaster Critical Review Form. Oral Se supplementation with 180 µg/day or 240 µg/day (selenomethionine) and 200 µg/day (Sodium Selenite), significantly decreased lipid hydroperoxide levels and increased GPx in plasma, erythrocyte, and muscle. No significant effects were observed on athletic performance, testosterone hormone levels, creatine kinase activity, and exercise training-induced adaptations on oxidative enzyme activities or on muscle fiber type myosin heavy chain expression. In addition, Se supplementation showed to have a dampening effect on the mitochondria changes in chronic and acute exercise. In summary, the use of Se supplem

04
SYSTEMATIC REVIEW Clinical nutrition ESPEN (2019) PMID: 31677697 ↗
Selenium supplementation in HIV-infected individuals: A systematic review of randomized controlled trials.
Clinical Trial Synthesis 2019 Systematic Review published in Clinical nutrition ESPEN. Key conclusion: However, we did not find quantifiable evidence that selenium supplementation suppresses or reduces HIV viral load.
View Original PubMed Abstract ↓

BACKGROUND & AIM: HIV infection has been linked to selenium deficiency which, in turn, is thought to be associated with a high risk of tuberculosis and mortality in HIV-infected patients. Furthermore, several trials have reported the beneficial effects of selenium supplementation in patients with HIV. However, the evidence remains inconclusive. Our study aimed to investigate whether daily selenium supplementation in patients infected with HIV delays the progression of HIV infection. METHODS: A systematic review was performed using EMBASE and Medline databases from January 2000 to June 2018. We included randomized clinical trials in adults comparing selenium with placebo and reporting outcomes including its effect on HIV viral load and cluster of differentiation 4 cell count (CD4). RESULTS: Six out of the 507 retrieved articles that met the inclusion criteria were used in this review. Reviewed studies show that daily supplementation with 200 μg selenium may improve the rate of cluster of differentiation 4 (CD4) count. The length of selenium supplementation and follow-up varied from 9 to 24 months. Supplements were well tolerated in all reviewed studies. Whether daily selenium supplementation in HIV-infected persons suppresses HIV-infection requires further investigation as existing data are heterogeneous. CONCLUSIONS: We found some clinical evidence that selenium supplementation can delay CD4 decline in HIV-infected patients, thus prolonging the onset of AIDS. However, we did not find quantifiable evidence that selenium supplementation suppresses or reduces HIV viral load.

05
CLINICAL STUDY Current rheumatology reviews (2019) PMID: 30324883 ↗
Selenium and Autoimmune Diseases: A Review Article.
Clinical Trial Synthesis 2019 Systematic Review published in Current rheumatology reviews. Key conclusion: Moreover, the majority of articles showed an improvement in clinical symptoms of collagen vascular diseases
View Original PubMed Abstract ↓

BACKGROUND: Selenium is an essential trace element with fundamental effects on human biology. Trace elements deficiency is not an uncommon finding in autoimmune diseases. This deficiency may be a consequence of autoimmune diseases or may contribute to their etiology. With regard to evidence showing the association between selenium deficiency and generation of reactive oxygen species and subsequent inflammation, reviewing the role of selenium in collagen vascular diseases could help researchers to devise strategies for managing these diseases. OBJECTIVE: The present study aimed to evaluate the role of selenium and autoimmune rheumatic diseases. DATA SOURCES: PubMed, Scopus, Science Direct, and Google Scholar. STUDY ELIGIBILITY CRITERIA: All the studies on the use of selenium without any limitations in terms of the preparation method, administration route, or formulation process were included in the study. The exclusion criteria were: 1) Articles published in languages other than English, 2) Administration of chemical and hormonal drugs rather than selenium, 3) Investigation of the effects of selenium on the autoimmune problems in animal models, and 4) Insufficiency of the presented data or poor description of the applied methods. Furthermore, review articles, meta-analyses, expert opinions, editorial letters, case reports, consensus statements, and qualitative studies were excluded from the study. DATA EXTRACTION: In this systematic review, articles were evaluated through searching following keywords in combination with selenium: "autoimmune rheumatic diseases "or "scleroderma" or "systemic sclerosis" or "Behcet's disease" or "Sjögren syndrome" or "systemic lupus erythematosus" or "musculoskeletal diseases" or "rheumatoid arthritis" or "vasculitis" or "seronegative arthritis" or "antiphospholipid antibody syndrome". RESULTS: Of 312 articles, 280 were excluded and 32 articles were entered in this study. Based on the majority of studies assessing selenium level in patients with collagen vascular diseases, lower selenium levels were observed in these patients. Moreover, the majority of articles showed an improvement in clinical symptoms of collagen vascular diseases

06
SYSTEMATIC REVIEW Acta bio-medica (2017) PMID: 29083329 ↗
Selenium Homeostasis and Clustering of Cardiovascular Risk Factors: A Systematic Review.
Clinical Trial Synthesis 2017 Systematic Review published in Acta bio-medica. Key conclusion: In addition, high levels of selenium may increase the risk of metabolic syndrome while the lack of sufficient selenium may also promote metabolic syndrome.
View Original PubMed Abstract ↓

Selenium is a trace element required for a range of cellular functions. It is widely used for the biosynthesis of the unique amino acid selenocysteine [Sec], which is a structural element of selenoproteins. This systematic review focused on the possible relation between selenium and metabolic risk factors. The literature was searched via PubMed, Scopus, ISI Web of Science, and Google Scholar. Searches were not restricted by time or language. Relevant studies were selected in three phases. After an initial quality assessment, two reviewers extracted all the relevant data, whereas the third reviewer checked their extracted data. All evidence came from experimental and laboratory studies. Selenoprotein P is the best indicator for selenium nutritional levels. In addition, high levels of selenium may increase the risk of metabolic syndrome while the lack of sufficient selenium may also promote metabolic syndrome. selenium supplementation in subjects with sufficient serum selenium levels has a contrary effect on blood pressure, LDL, and total cholesterol. According to the bioavailability of different types of selenium supplementation such as selenomethionine, selenite and selenium-yeast, it seems that the best nutritional type of selenium is selenium-yeast. Regarding obtained results of longitudinal studies and randomized controlled trials, selenium supplementation should not be recommended for primary or secondary cardio-metabolic risk prevention in populations with adequate selenium status.

07
META-ANALYSIS Nutrients (2014) PMID: 25268836 ↗
Selenium-enriched foods are more effective at increasing glutathione peroxidase (GPx) activity compared with selenomethionine: a meta-analysis.
Clinical Trial Synthesis 2014 Meta-Analysis published in Nutrients; statistical significance reported at p = 0.001. Key conclusion: The meta-analysis identified that for animal species selenium-enriched foods were more effective than selenomethionine at increasing GPx activity.
View Original PubMed Abstract ↓

Selenium may play a beneficial role in multi-factorial illnesses with genetic and environmental linkages via epigenetic regulation in part via glutathione peroxidase (GPx) activity. A meta-analysis was undertaken to quantify the effects of dietary selenium supplementation on the activity of overall GPx activity in different tissues and animal species and to compare the effectiveness of different forms of dietary selenium. GPx activity response was affected by both the dose and form of selenium (p < 0.001). There were differences between tissues on the effects of selenium supplementation on GPx activity (p < 0.001); however, there was no evidence in the data of differences between animal species (p = 0.95). The interactions between dose and tissue, animal species and form were significant (p < 0.001). Tissues particularly sensitive to changes in selenium supply include red blood cells, kidney and muscle. The meta-analysis identified that for animal species selenium-enriched foods were more effective than selenomethionine at increasing GPx activity.

08
CLINICAL STUDY The Cochrane database of systematic reviews (2013) PMID: 23744563 ↗
Selenium supplementation for Hashimoto's thyroiditis.
Clinical Trial Synthesis 2013 Meta-Analysis published in The Cochrane database of systematic reviews involving n = 463 participants. Key conclusion: One study at high risk of bias showed statistically significant improvement in subjective well-being with sodium selenite 200 μg plus titrated LT4 compared with placebo plus titrated LT4 (relative risk (RR) 4.67, 95% confide
View Original PubMed Abstract ↓

BACKGROUND: Hashimoto's thyroiditis is a common auto-immune disorder. The most common presenting symptoms may include anxiety, negative mood, depression, dry skin, cold intolerance, puffy eyes, muscle cramps and fatigue, deep voice, constipation, slow thinking and poor memory. Clinical manifestations of the disease are defined primarily by low levels of thyroid hormones; therefore it is treated by hormone replacement therapy, which usually consists of levothyroxine (LT4). Selenium might reduce antibody levels and result in a decreased dosage of LT4 and may provide other beneficial effects (e.g. on mood and health-related quality of life). OBJECTIVES: To assess the effects of selenium supplementation on Hashimoto's thyroiditis. SEARCH METHODS: We searched the following databases up to 2 October 2012: CENTRAL in The Cochrane Library (2012, Issue 10), MEDLINE, EMBASE, and Web of Science; we also screened reference lists of included studies and searched several online trial registries for ongoing trials (5 November 2012). SELECTION CRITERIA: Randomised controlled clinical trials that assessed the effects of selenium supplementation for adults diagnosed with Hashimoto's thyroiditis. DATA COLLECTION AND ANALYSIS: Study selection, data extraction, assessment of risk of bias, and analyses were carried out by two independent review authors. We assessed the quality of the evidence of included studies using GRADE. We were unable to conduct a meta-analysis because clinical heterogeneity between interventions that were investigated is substantial. MAIN RESULTS: Four studies at unclear to high risk of bias comprising 463 participants were included. The mean study duration was 7.5 months (range 3 to 18 months). One of our primary outcomes-'change from baseline in health related quality of life'-and two of our secondary outcomes-'change from baseline in LT4 replacement dosage at end of the study' and 'economic costs'-were not assessed in any of the studies. One study at high risk of bias showed statistically significant improvement in subjective well-being with sodium selenite 200 μg plus titrated LT4 compared with placebo plus titrated LT4 (relative risk (RR) 4.67, 95% confide

09
CLINICAL STUDY The Cochrane database of systematic reviews (2013) PMID: 23728666 ↗
Interventions for clinical and subclinical hypothyroidism pre-pregnancy and during pregnancy.
Clinical Trial Synthesis 2013 Randomized Controlled Trial (RCT) published in The Cochrane database of systematic reviews involving n = 362 participants (RR 0.28). Key conclusion: AUTHORS' CONCLUSIONS: This review found no dif
View Original PubMed Abstract ↓

BACKGROUND: Over the last decade there has been enhanced awareness of the appreciable morbidity of thyroid dysfunction, particularly thyroid deficiency. Since treating clinical and subclinical hypothyroidism may reduce adverse obstetric outcomes, it is crucial to identify which interventions are safe and effective. OBJECTIVES: To identify interventions used in the management of hypothyroidism and subclinical hypothyroidism pre-pregnancy or during pregnancy and to ascertain the impact of these interventions on important maternal, fetal, neonatal and childhood outcomes. SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2013). SELECTION CRITERIA: Randomised controlled trials (RCTs) and quasi-randomised controlled trials that compared a pharmacological intervention for hypothyroidism and subclinical hypothyroidism pre-pregnancy or during pregnancy with another intervention or placebo. DATA COLLECTION AND ANALYSIS: Two review authors assessed trial eligibility and quality and extracted the data. MAIN RESULTS: We included four RCTs of moderate risk of bias involving 362 women. In one trial of 115 women, levothyroxine therapy to treat pregnant euthyroid (normal thyroid function) women with thyroid peroxidase antibodies was not shown to reduce pre-eclampsia significantly (risk ratio (RR) 0.61; 95% confidence interval (CI) 0.11 to 3.48) but did significantly reduce preterm birth by 72% (RR 0.28; 95% CI 0.10 to 0.80). Two trials of 30 and 48 hypothyroid women respectively compared levothyroxine doses, but both trials reported only biochemical outcomes. A trial of 169 women compared the trace element selenomethionine (selenium) with placebo and no significant differences were seen for either pre-eclampsia (RR 1.44; 95% CI 0.25 to 8.38) or preterm birth (RR 0.96; 95% CI 0.20 to 4.61). None of the four trials reported on childhood neurodevelopmental delay.There was a non-significant trend towards fewer miscarriages with levothyroxine, and selenium showed some favourable impact on postpartum thyroid function and a decreased incidence of moderate to advanced postpartum thyroiditis. AUTHORS' CONCLUSIONS: This review found no dif

10
CLINICAL STUDY The Cochrane database of systematic reviews (2011) PMID: 21563143 ↗
Selenium for preventing cancer.
Clinical Trial Synthesis 2011 Randomized Controlled Trial (RCT) published in The Cochrane database of systematic reviews (OR 0.55). Key conclusion: AUTHORS' CONCLUSIONS: No reliable conclusions can be drawn regarding a causal relationship between low selenium exposure and an increased risk of cancer.
View Original PubMed Abstract ↓

BACKGROUND: Selenium is a trace element essential to humans. Higher selenium exposure and selenium supplements have been suggested to protect against several types of cancers. OBJECTIVES: Two research questions were addressed in this review: What is the evidence for1. an aetiological relationship between selenium exposure and cancer risk in women and men?2. the efficacy of selenium supplementation for cancer prevention in women and men? SEARCH STRATEGY: We searched electronic databases and bibliographies of reviews and included publications. SELECTION CRITERIA: We included prospective observational studies to answer research question (a) and randomised controlled trials (RCTs) to answer research question (b). DATA COLLECTION AND ANALYSIS: We conducted random effects meta-analyses of epidemiological data when five or more studies were retrieved for a specific outcome. We made a narrative summary of data from RCTs. MAIN RESULTS: We included 49 prospective observational studies and six RCTs. In epidemiologic data, we found a reduced cancer incidence (summary odds ratio (OR) 0.69 (95% confidence interval (CI) 0.53 to 0.91) and mortality (OR 0.55, 95% CI 0.36 to 0.83) with higher selenium exposure. Cancer risk was more pronouncedly reduced in men (incidence: OR 0.66, 95% CI 0.42 to 1.05) than in women (incidence: OR 0.90, 95% CI 0.45 to 1.77). These findings have potential limitations due to study design, quality and heterogeneity of the data, which complicated the interpretation of the summary statistics.The RCTs found no protective efficacy of selenium yeast supplementation against non-melanoma skin cancer or L-selenomethionine supplementation against prostate cancer. Study results for the prevention of liver cancer with selenium supplements were inconsistent and studies had an unclear risk of bias. The results of the Nutritional Prevention of Cancer Trial (NPCT) and SELECT raised concerns about possible harmful effects of selenium supplements. AUTHORS' CONCLUSIONS: No reliable conclusions can be drawn regarding a causal relationship between low selenium exposure and an increased risk of cancer. Despite evidence for an inverse association between selenium exposure

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