Selenium

Selenium is an essential trace element found mostly in animal foods and in Brazil nuts, and a small 2025 trial found lower selenium intake in adults following a vegan diet than in omnivores, with Brazil nut butter raising selenium status as well as a supplement did. Large, well-conducted randomised trials found that selenium supplements did not lower cancer or cardiovascular risk in adults, and pooled trials suggest a small increase in type 2 diabetes risk. In people with Hashimoto thyroiditis, trials found lower thyroid antibody and TSH levels with selenium. Intakes above the EFSA upper level are possible with high-dose supplements or regular Brazil nut eating.

Longevity
Vegan

Evidence retrieved up to 15 October 2026

What the research shows

In a randomised trial of adults following vegan or omnivorous diets, Brazil nut butter raised serum selenium and selenoprotein P as effectively as a selenium supplement.

Low certainty

Further research is likely to change this.

Take care: see the safety noteBenefit

Who this is about

adults following vegan or omnivorous diets

Practical note

Graded low: one randomised trial of 86 adults lasting two weeks, measuring blood markers rather than health outcomes. The trial added 55 micrograms of selenium a day, and its authors describe Brazil nuts as suitable when consumed once in a while.

Vegan note

Brazil nuts are the main plant-based food with high selenium content.

Safety note

The selenium content of Brazil nuts is highly variable, and EFSA names regular consumers of Brazil nuts among the adults who may exceed its tolerable upper intake level of 255 micrograms a day.

Sources

Supports “Independent of the dietary pattern (vegan or omnivore), Brazil nut butter as well as supplement significantly increased serum selenium and SELENOP concentrations, while there were no changes in the placebo groups.” (Abstract, Results) Simon R, Lossow K, Pellowski D, Kipp K, Achatz M, Klasen N, Schwerdtle T, Dawczynski C, Kipp AP. 2025. European Journal of Nutrition. Improving the selenium supply of vegans and omnivores with Brazil nut butter compared to a dietary supplement in a randomized controlled trial. CC BY (per Europe PMC and OpenAlex metadata); credit Simon et al., European Journal of Nutrition 2025
Context “Based on available intake data, adult consumers are unlikely to exceed the UL, except for regular users of food supplements containing high daily doses of selenium or regular consumers of Brazil nuts.” (Abstract) EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA); Turck D, Bohn T, Castenmiller J, et al. 2023. EFSA Journal. Scientific opinion on the tolerable upper intake level for selenium. publisher copyright; metadata and short quotes only; Courtesy of the U.S. National Library of Medicine

Selenium supplementation was linked to a small increase in the risk of type 2 diabetes in pooled randomised trials, and higher blood selenium was linked to higher diabetes risk in observational studies.

Low certainty

Further research is likely to change this.

Take care: see the safety noteRisk

Who this is about

adults

Practical note

Graded low: the trial estimate (risk ratio 1.11, 95% CI 1.01 to 1.22) rests on 5 trials of 200 micrograms a day and sits close to no effect, and an earlier Cochrane analysis found a similar but non-significant increase (risk ratio 1.06, 95% CI 0.97 to 1.15); downgraded for imprecision and inconsistency.

Safety note

This is one reason high-dose selenium supplements are not considered harmless for adults whose selenium intake is already adequate.

Sources

Supports “Overall, results from both nonexperimental and experimental studies indicate that selenium may increase the risk of type 2 diabetes across a wide range of exposure levels.” (Abstract) Vinceti M, Filippini T, Rothman KJ. 2018. European Journal of Epidemiology. Selenium exposure and the risk of type 2 diabetes: a systematic review and meta-analysis. publisher copyright; metadata and short quotes only; Courtesy of the U.S. National Library of Medicine
Context “There was a small increased risk of type 2 diabetes with selenium supplementation but this did not reach statistical significance (RR 1.06, 95% CI 0.97 to 1.15).” (Abstract, Main results) Rees K, Hartley L, Day C, Flowers N, Clarke A, Stranges S. 2013. Cochrane Database of Systematic Reviews. Selenium supplementation for the primary prevention of cardiovascular disease. publisher copyright; metadata and short quotes only; Courtesy of the U.S. National Library of Medicine

Adults following a vegan diet in Europe had lower estimated selenium intake than omnivores, and intake tracked their blood selenium markers.

Low certainty

Further research is likely to change this.

No known concerns at usual amountsRisk

Who this is about

adults following a vegan diet in Europe

Practical note

Graded low: the comparison comes from baseline data of one small German trial (86 adults) using five-day dietary records, so it is observational and imprecise.

Vegan note

Plant foods are generally lower in selenium than animal foods; Brazil nuts are the main high-selenium plant food.

Sources

Supports “The estimated selenium intake was significantly lower in vegans compared to omnivores and correlated with all three selenium biomarkers.” (Abstract, Results) Simon R, Lossow K, Pellowski D, Kipp K, Achatz M, Klasen N, Schwerdtle T, Dawczynski C, Kipp AP. 2025. European Journal of Nutrition. Improving the selenium supply of vegans and omnivores with Brazil nut butter compared to a dietary supplement in a randomized controlled trial. CC BY (per Europe PMC and OpenAlex metadata); credit Simon et al., European Journal of Nutrition 2025
Context “Due to the lower selenium content in plant-based compared to animal-based foods, many vegans do not reach the recommended selenium intake in Europe.” (Abstract, Purpose) Simon R, Lossow K, Pellowski D, Kipp K, Achatz M, Klasen N, Schwerdtle T, Dawczynski C, Kipp AP. 2025. European Journal of Nutrition. Improving the selenium supply of vegans and omnivores with Brazil nut butter compared to a dietary supplement in a randomized controlled trial. CC BY (per Europe PMC and OpenAlex metadata); credit Simon et al., European Journal of Nutrition 2025

In well-conducted randomised trials in adults, mostly men, selenium supplements did not lower overall cancer risk, and some trials reported more high-grade prostate cancer and type 2 diabetes with supplementation.

High certainty

Further research is very unlikely to change this.

Take care: see the safety noteNo clear effect

Who this is about

adults, predominantly men, in randomised trials

Practical note

Graded high for the no-benefit finding on overall cancer incidence: three low-risk-of-bias trials with 19,475 participants gave a risk ratio of 1.01 (95% CI 0.93 to 1.10). Applicability to women is less certain because 88 percent of trial participants were men. Cohort studies linking higher selenium to lower cancer risk were judged very low certainty because of confounding.

Safety note

In the largest trial (SELECT) selenium supplementation also increased hair loss and dermatitis.

Sources

Supports “Well-designed and well-conducted RCTs have shown no beneficial effect of selenium supplements in reducing cancer risk (high certainty of evidence).” (Abstract, conclusions) Vinceti M, Filippini T, Del Giovane C, Dennert G, Zwahlen M, Brinkman M, Zeegers MP, Horneber M, D'Amico R, Crespi CM. 2018. Cochrane Database of Systematic Reviews. Selenium for preventing cancer. publisher copyright; metadata and short quotes only; Courtesy of the U.S. National Library of Medicine
Context “Some RCTs have raised concerns by reporting a higher incidence of high-grade prostate cancer and type 2 diabetes in participants with selenium supplementation.” (Abstract, conclusions) Vinceti M, Filippini T, Del Giovane C, Dennert G, Zwahlen M, Brinkman M, Zeegers MP, Horneber M, D'Amico R, Crespi CM. 2018. Cochrane Database of Systematic Reviews. Selenium for preventing cancer. publisher copyright; metadata and short quotes only; Courtesy of the U.S. National Library of Medicine

In randomised trials in adults from the general population and at high cardiovascular risk, selenium-only supplements did not lower all-cause mortality, cardiovascular deaths or cardiovascular events.

Moderate certainty

Further research may change the size of the effect.

Take care: see the safety noteNo clear effect

Who this is about

adults from the general population and adults at high cardiovascular risk

Practical note

Graded moderate: 12 trials with 19,715 participants at low risk of bias, but clinical events came mainly from two US trials and the review search ended in 2012, so downgraded one level for indirectness to other populations.

Safety note

The same trials reported more hair loss and mild dermatitis with selenium supplementation.

Sources

Supports “The limited trial evidence that is available to date does not support the use of selenium supplements in the primary prevention of CVD.” (Abstract, conclusions) Rees K, Hartley L, Day C, Flowers N, Clarke A, Stranges S. 2013. Cochrane Database of Systematic Reviews. Selenium supplementation for the primary prevention of cardiovascular disease. publisher copyright; metadata and short quotes only; Courtesy of the U.S. National Library of Medicine

As part of a healthy lifestyle, selenium may help people living well with Hashimoto thyroiditis: in randomised trials, selenium supplements lowered thyroid peroxidase antibody levels and, in those not taking thyroid hormone, TSH levels.

Low certainty

Further research is likely to change this.

Take care: see the safety noteBenefit

Who this is about

adults living with Hashimoto thyroiditis

Practical note

Graded low: the review authors rated overall certainty moderate, but the antibody result was very heterogeneous (I2 90 percent across 29 cohorts) and both outcomes are blood markers rather than how people feel, so downgraded a further level for indirectness. Adverse effects were similar to control.

Safety note

Thyroid conditions are managed with a health professional; the trials measured blood markers, not symptoms.

Sources

Supports “In people with HT without THRT, selenium was effective and safe in lowering TSH, TPOAb, and MDA levels.” (Abstract, Conclusions) Huwiler VV, Maissen-Abgottspon S, Stanga Z, Mühlebach S, Trepp R, Bally L, Bano A. 2024. Thyroid. Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. publisher copyright; metadata and short quotes only; Courtesy of the U.S. National Library of Medicine