Instead, the review emphasizes mechanistic and observational evidence to explain how optimal selenium intake and selenium status may be important. At the same time, the authors point out that both selenium deficiency and selenium excess can be detrimental. There seems to be a U-shaped relationship between selenium status and good health and longevity [Pierce & Mackrill 2026].
Chen et al say that “oxidative stress, redox signaling, endothelial activation, and inflammation contribute to atherosclerosis and myocardial injury”. So, there is a mechanistic rationale for selenium to have a cardioprotective effect. “Selenium-dependent enzymes provide a plausible connection because glutathione peroxidases and thioredoxin reductases participate in peroxide reduction and redox regulation” [Chen 2026].
Generally, observational studies show low selenium status associated with increased risk of cardiovascular diseases. However, interventional studies have not shown clearly that selenium supplementation reduces the risk of cardiovascular diseases [Chen 2026].
Chen et al analyzed the relevant research for the period 2005-2026. They concluded that there is not enough evidence to support a program of universal selenium supplement for protection against cardiovascular disease [Chen 2026].
Higher biomarker levels of selenium status correlate significantly with lower mortality rates. This is the conclusion of a 2025 meta-analysis of 20 cohort studies. Importantly, the central finding in the meta-analysis was a consistent inverse association between selenium status and mortality [Cui, Schomburg et al 2025].
Basically, one standard deviation increase in selenium status corresponded to the following reduction in mortality:
Moreover, Cui et al found low serum Selenoprotein P (SELENOP) concentrations associated with an increased risk of stroke in subjects free of cardiovascular disease and with increased risk of cardiovascular mortality among heart disease patients. The association of SELENOP concentrations with cardiovascular disease incidence was restricted to patients with hypertension or diabetes [Cui 2025].
We need more clinical studies of the topic. However, here is what we know:
Children in chemotherapy often have low serum selenium status. The reasons include low dietary selenium intake, increased oxidative stress, and altered metabolism [Podpeskar 2023].
Delgado et al investigated the extent to which selenium supplementation can modulate antioxidant defense mechanisms and inflammation in children and adolescents undergoing treatment for cancer. The researchers knew that children need selenium to regulate immune function and oxidative stress.
Sufficient selenium is essential for normal thyroid hormone synthesis and activation. Furthermore, selenium is important for protection of the thyroid gland against oxidative stress. Note that both selenium deficiency and excessive intake can impair thyroid health [Gorini 2021].
Several selenium-dependent enzymes catalyze thyroid hormone synthesis and activation. Similarly, selenoenzymes provide antioxidant protection against oxidative damage [Gorini 2021].
Importantly, selenium is incorporated into deiodinases. These enzymes convert the T4 hormone into the biologically active hormone T3. In addition, antioxidant selenoenzymes such as the glutathione peroxidases and the thioredoxin reductases neutralize hydrogen peroxide radicals that are generated during thyroid hormone production [Gorini 2021].
Answer: The strongest evidence is from studies of patients with Graves’ orbitopathy.
Answer: GO, also known as thyroid eye disease, is an inflammatory autoimmune disorder. It affects the tissues around the eyes. It causes swelling and discomfort. Most frequently, it affects individuals who have Graves’ disease [Cleveland Clinic 2026].
What does the clinical evidence show about selenium supplementation and Graves’ orbitopathy?
Answer: In 2026, Kostadinov et al examined data from five RCTs including 303 patients with Graves’ Orbitopathy. 165 patients received selenium; 138 received placebo or no selenium. Selenium supplementation resulted in a significant reduction in clinical activity score. However, the meta-analysis showed no significant differences in Quality of Life improvement or in visual function [Kostadinov 2026].
Sufficient selenium is essential for normal thyroid hormone synthesis and activation. Furthermore, selenium is important for protection of the thyroid gland against oxidative stress. Note that both deficiency and excessive intake can impair thyroid health [Gorini 2021].
Several selenium-dependent enzymes catalyze thyroid hormone synthesis and activation. Similarly, selenoenzymes provide antioxidant protection against oxidative damage [Gorini 2021].
Importantly, selenium is incorporated into deiodinases. These enzymes convert the T4 hormone into the biologically active hormone T3. In addition, antioxidant selenoenzymes such as the glutathione peroxidases and the thioredoxin reductases neutralize hydrogen peroxide radicals that are generated during thyroid hormone production [Gorini 2021].
In a 2026 Norwegian study, researchers examined and compared epicardial adipose tissue biopsies from two groups of heart disease patients [Opstad 2026]:
The heart valve disease patients had lower vulnerability to elevated inflammation levels. As such, they served as a control group to the group of coronary artery disease patients.
The research team obtained the epicardial adipose tissue biopsies during open-chest heart surgery. They measured selenium concentrations in the blood circulation and in the epicardial adipose tissue of the heart disease patients.
The Cleveland Clinic explains that the epicardium is the outer layer of the heart muscle and the inner layer of the pericardium that surrounds the heart. A layer of fat (= adipose tissue) separates the epicardium from the heart muscle. The epicardium protects the heart and helps the heart function [Cleveland Clinic staff 2025].
Over time, many breast tumors become resistant to chemotherapy. Thus, drug-resistant tumors limit the success of anti-cancer therapies. Numerous mechanisms decrease the intracellular accumulation of anti-cancer drugs. In this way, breast cancer tumors become less responsive to the chemotherapy [Baier 2026].
Selenium is an essential trace element. Through the activity of selenoproteins, selenium is involved in the following potentially anti-cancer activities [Baier 2026]:
Note: Cancer cells often rely on altered redox balance. Accordingly, selenium compounds may disrupt tumor survival mechanisms. At the same time, they can spare normal cells and tissues.
In a 2026 review, Baier et al make the point that multi-drug resistance in breast cancer often stems from several resistance pathways acting together. Thus, selenium-containing compounds may help overcome breast cancer patients’ multi-drug resistance via overlapping multiple mechanisms:
First of all, during pregnancy, biomarkers of selenium status decline considerably. In some pregnancies, the blood level of selenium falls to critically low levels [Schomburg 2021].
Secondly, the decline in selenium status during pregnancy reflects an increased need for selenium. During the pregnancy, both the mother and the developing fetus need selenium. The mother transfers selenium to the fetus via the placenta [Schomburg 2021].
Thirdly, low selenium status during pregnancy is associated with health risks [Schomburg 2021; Shreenath et al 2023]:
Fourthly, selenium supplementation may be necessary in some cases. To date, the evidence base in support of selenium supplementation during pregnancy is somewhat limited. At this point, we need more randomized controlled trials. However, it is clear that adequate selenium status during pregnancy is important for good immune system function and for preventing the development of autoimmune conditions [Schomburg 2021].
