The Impact of Selenium and Selenoproteins on Human Health

Selenium is an essential trace mineral that typically functions by being incorporated into selenoproteins. Selenoproteins play diverse physiological roles, including antioxidant and anti-inflammatory activities and the promotion of active thyroid hormone synthesis. Furthermore, selenium is crucial for immune system function, defense against pathogens, and the inhibition of cancer progression. It can be obtained through dietary sources—such as nuts, fish, eggs, meat, shiitake mushrooms, and brown rice—or via dietary supplements[1-2].

Selenium Levels and Related Conditions

Low Selenium Status

Research indicates that low selenium status is associated with increased mortality, impaired immune function, and cognitive decline. It may lead to symptoms such as garlic-like breath, hair loss, nail loss, neurological and skin disorders, and poor dental health. In women, selenium deficiency is linked to early and recurrent miscarriage; in men, it may result in reduced sperm motility and infertility. Selenium deficiency can directly cause Keshan disease (a type of cardiomyopathy) and Kashin-Beck disease (an osteoarthropathy). Additionally, it increases the risks associated with viral mutation, virulence, and disease progression, and is closely linked to the onset and development of autoimmune thyroid diseases (such as Hashimoto's thyroiditis and Graves' ophthalmopathy).

High Selenium Levels

Higher selenium levels or supplementation exert antiviral effects, are vital for reproductive function in both men and women, and can reduce the risk of autoimmune thyroid diseases. Multiple prospective studies suggest that higher selenium levels offer benefits in reducing the risk of prostate, lung, colorectal, and bladder cancers. However, results from clinical trials have been mixed. This implies that supplementation is beneficial primarily when there is an underlying nutritional deficiency. While extra selenium benefits those with low selenium status, it may increase the risk of type 2 diabetes in individuals who already have adequate or high selenium levels.

Benefits of Selenium Supplementation

As a dietary supplement, selenium not only effectively ameliorates conditions associated with selenium deficiency but also helps scavenge reactive oxygen species, protecting cells from oxidative damage; it facilitates the conversion of inactive thyroxine (T4) into active triiodothyronine (T3) and enhances T-cell proliferation, natural killer cell activity, and antiviral immune responses. Dietary selenium intake ranges from 7 µg to 4,990 µg per day; the average intake is 40 µg/day in Europe, while in the United States, it ranges from 93 µg/day (for women) to 134 µg/day (for men). However, it should be noted that individuals with serum selenium levels exceeding 122 µg/L should not take additional selenium supplements, so as to avoid adverse reactions.

References

[1] RAYMAN M P. Selenium and human health.[J]. Lancet (London, England), 2012, 379 9822: 1256-1268. DOI:10.1016/S0140-6736(11)61452-9.

[2] RAYMAN M P. The importance of selenium to human health.[J]. Lancet (London, England), 2000, 356 9225: 233-241. DOI:10.1016/S0140-6736(00)02490-9.