Selenium Benefits: Eye Health, Immune Function, & Antioxidant Support

What Is Selenium?

Selenium is an essential trace mineral that plays a key role in antioxidant protection, immune function, thyroid hormone metabolism, and cellular health. Selenium-dependent enzymes help protect tissues from oxidative stress and support many important physiological processes throughout the body. Low selenium status has been associated with impaired immune function, reduced antioxidant protection, and compromised thyroid function.¹

Benefits of Selenium

Antioxidant Support

Maintaining proper selenium levels appears important in promoting health due to its antioxidant effects. Specifically, selenium functions primarily as a component of the antioxidant enzyme glutathione peroxidase, which works with vitamin E in preventing free radical damage to cell membranes. Maintaining adequate selenium status appears important for overall health and healthy aging. Human studies have shown that selenium-rich yeast may offer advantages compared to some other forms of selenium in supporting antioxidant activity and reducing markers of oxidative stress. For example, in one double-blind, placebo-controlled trial, 69 healthy men were given selenium from a selenium-rich yeast called SelenoExcell (200 or 285 μg/day) or selenomethionine (200 μg/day) for nine months. While blood selenium levels increased by 93%, 54%, and 86% in the selenomethionine and low- and high-dose SelenoExcell groups, respectively, only the men receiving the SelenoExcell demonstrated a decrease in standard markers of oxidative damage.²

Eye Health

Adequate selenium intake may help support healthy eye tissues by contributing to antioxidant defense systems in the lens and surrounding structures. Selenium-dependent enzymes help protect tissues from oxidative damage associated with aging. Studies have shown that the selenium content in the human lens with an age-related opacity is only 15% of normal levels, and levels of free radicals are up to 25 times the normal levels in the aqueous humor (eye fluid) in patients with suboptimal lens clarity.³

Cardiovascular Health

Selenium  plays an important role in maintaining healthy cardiovascular function through its effects on antioxidant protection, inflammatory balance, and cellular metabolism. Observational studies have noted associations between adequate selenium intake and cardiovascular wellness, although maintaining overall healthy lifestyle habits remains essential. In one double-blind study, 81 patients seeking cardiovascular support were randomly assigned to receive 100 mcg of selenium (from selenium-rich yeast) or a placebo. After six months, significant improvements were noted in the selenium group in terms of support for healthy heart function.⁴

Immune Function

Selenium affects all components of the immune system, including the development and expression of all white blood cells. Selenium deficiency has been shown to depress immune function and lower natural defenses against environmental threats, whereas supplementing with 200 mcg/day can help stimulate and restore white blood cell and thymus function.⁵

Human studies demonstrate that selenium supplementation may enhance several markers of immune function, particularly in individuals with low selenium status. For example, in one study, selenium supplementation (200 mcg/day) in individuals with normal blood selenium levels increased the ability of white blood cells to target cellular threats by 118%.⁶

Pregnancy

There is substantial evidence that selenium is essential for proper fetal growth and development. Selenium requirements appear to be increased during pregnancy as selenium concentrations in the blood tend to be lower during pregnancy, particularly during the later stages. Selenium levels tend to be very low in low birthweight babies.⁷

Thyroid Function

Selenium is essential for the proper function of the thyroid. Low levels of selenium in the thyroid are associated with thyroid dysfunction. To prevent low levels of selenium, the thyroid accumulates, retains, and recycles selenium differently than other tissues. The selenium content in the thyroid is not related to blood selenium levels, and there is no marker yet that reflects thyroid selenium status. Maintaining an adequate dietary intake of selenium appears to be the best way to supply sufficient levels of selenium to the thyroid.^8,9

In a double-blind, placebo-controlled clinical study involving individuals with suboptimal thyroid health, supplementation with 200 mcg of selenium (as selenomethionine) daily for 60 days was associated with support for antioxidant status and thyroid health.¹⁰

Forms of Selenium

Popular forms of selenium on the market include sodium selenite, selenomethionine, and yeast-derived selenium. Several studies have shown that inorganic salts like sodium selenite are less effectively absorbed and not as biologically active compared to organic forms of selenium, such as selenomethionine and selenium-rich yeast. In addition, several studies have shown advantages with high selenium content yeast (e.g., SelenoExcell), making it the preferred form of selenium supplement.²

Suggested Intake and Safety

The usual dosage recommendation for selenium supplementation is 50 to 200 mcg per day. Selenium should be used within this recommended intake level, as excessive intake over prolonged periods may lead to selenium toxicity. Signs of excessive selenium intake may include gastrointestinal upset, brittle hair or nails, fatigue, irritability, and a garlic-like odor on the breath.

References:

1. National Institutes of Health Office of Dietary Supplements. Selenium Fact Sheet for Health Professionals. Updated 2025.
2. Richie JP Jr, Das A, Calcagnotto AM, et al. Comparative effects of two different forms of selenium on oxidative stress biomarkers in healthy men: a randomized clinical trial. Cancer Prev Res (Phila). 2014 Aug;7(8):796-804.
3. Karakucuk S, Ertugrul Migra G, Faruk Ekinciler O. Selenium concentrations in serum, lens, and aqueous humour of patients with senile cataract. Arch Ophthalmol Scand 1995; 73: 329–332.
4. Korpela H, Kumpulainen J, Jussila E, et al. Effect of selenium supplementation after acute myocardial infarction. Res Commun Chem Pathol Pharmacol. 1989 Aug;65(2):249-52.
5. Xia X, Zhang X, Liu M, et al. Toward improved human health: efficacy of dietary selenium on immunity at the cellular level. Food Funct. 2021;12(3):976-989.
6. Kiremidjian-Schumacher L, Roy M, Wishe HI, et al. Supplementation with selenium and human immune cell functions. II. Effect on cytotoxic lymphocytes and natural killer cells. Biol Trace Elem Res 1994;41:115-127.
7. Hogan C, Perkins AV. Selenoproteins in the Human Placenta: How Essential Is Selenium to a Healthy Start to Life?. Nutrients. 2022;14(3):628.
8. Gorini F, Sabatino L, Pingitore A, Vassalle C. Selenium: An Element of Life Essential for Thyroid Function. Molecules. 2021;26(23):7084.
9. Winther KH, Rayman MP, Bonnema SJ, Hegedüs L. Selenium in thyroid disorders - essential knowledge for clinicians. Nat Rev Endocrinol. 2020;16(3):165-176.
10. Hajyasini A, Dehnad A, Farzi A, et al. Effect of Selenomethionine- Enriched Yeast on Hypothyroidism Patients. Arch Razi Inst. 2025 Feb 1;80(1):257-261.