Introduction
Selenium, also known as Se, is a powerful antioxidant in the human diet, and it has important effects on the body by being a part of selenoproteins. These proteins help control reactive oxygen species (ROS) and the balance of redox in the human tissues, influencing inflammation and immune responses. While some studies support the idea that selenium can strengthen the immune system, especially in aging or protection against certain infections, research suggests that more selenium might not always be good, especially for responses like fighting parasites or dealing with allergic asthma. This article explains how different levels of selenium affect various aspects of the immune system. Understanding these effects will help in using selenium supplements more effectively to treat diseases related to the immune system.
What Is the Importance of Selenium?
Selenium, also known as Se, is a vital nutrient essential for human health. It plays a key role in various aspects of well-being, such as thyroid hormone regulation, heart health, preventing neurodegeneration and cancer, and supporting a strong immune system. However, having too little or too much selenium in the diet can be harmful, and extreme levels can even be fatal. While severe deficiency or toxicity is rare, subtle changes in selenium levels can impact inflammation and immune responses. Selenium's effects are mainly seen through its incorporation into selenoproteins, which are involved in activating and regulating cells that drive our immune system. Not only do dietary selenium and selenoproteins support the initiation and enhancement of immunity, but they also help regulate the immune response, preventing excessive reactions that could lead to issues like autoimmune conditions or chronic inflammation.
What Is the Role of Selenium in Various Aspects of Immunity?
1. Role of Selenium in Viral Infections:
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One notable source of information on the harmful effects of low selenium (Se) levels comes from studies on Keshan disease. This heart condition affects people in regions with soils lacking selenium. Supplementing individuals with selenium has been shown to prevent Keshan disease. The disease is partially linked to a specific virus (coxsackievirus) and selenium not only boosts antiviral immunity but also prevents the virus from becoming more dangerous.
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In mouse studies with influenza A, another RNA virus, researchers found that selenium deficiency led to increased mutations in the virus's genetic material. Selenium-deficient mice infected with the flu showed higher inflammation levels, possibly due to increased oxidative stress. Moreover, the deficiency affected cell-mediated immunity more than antibody-based immunity in responding to the virus.
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Selenium's role extends to human immunodeficiency virus-1 (HIV-1). HIV-1-infected individuals with lower selenium levels have been associated with lower CD4+ T cell counts, faster disease progression, and higher mortality. Daily selenium supplementation has been linked to a slower progression of HIV-1 viral burden and improved CD4+ T cell count.
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Poliovirus, another example, shows increased immune responses with selenium supplementation. Subjects with low selenium levels who received supplementation exhibited enhanced production of certain immune molecules in response to a polio vaccine, leading to faster clearance of the virus.
All these findings suggest that selenium can influence the strength and efficiency of the immune response against viral infections.
2. Role of Selenium in Immunity to Non-Viral Pathogens:
While having higher selenium (Se) levels is generally linked to protection against viruses, the connection between a person's Se status and immunity to non-viral pathogens is more complex. The available data suggest that the impact of Se status on resistance to bacterial, parasitic, and fungal infections depends on the specific microorganism involved.
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In a study on mice infected with Candida albicans, a fungus causing infections, those with Se deficiency were more susceptible to the pathogen. The study revealed that Se-deficient mice had neutrophils (a type of immune cell) with impaired abilities to kill the fungus.
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Se deficiency did not affect the killing of bacteria like Salmonella typhimurium and Staphylococcus aureus by neutrophils. Se deficiency increased the mortality of rats injected with Staphylococcus aureus, but it increased the survival of rats infected with other pathogens like Salmonella typhimurium, Plasmodium bergeii, or Listeria monocytogenes.
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In a more recent study, mice deficient in Se but infected with Trypanosoma musculi, a specific parasite for mice, were able to clear the infection, unlike mice with sufficient Se levels. The explanation proposed was that the parasite lacks the ability to manage oxidative stress without the host's Se-sufficient antioxidants. However, the Se-deficient mice had lower antibody responses, suggesting that persistent infection or Se sufficiency is essential for proper antibody production against such parasitic pathogens.
3. Role of Selenium in Cancer Immunity:
Growing evidence from both basic and clinical studies in humans suggests that dietary selenium (Se) may have a protective role against various types of cancer.
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The Nutritional Prevention of Cancer Trial investigated the impact of high Se yeast on cancer incidence and mortality. The results indicated a potential decrease in the risk of colorectal cancer, prostate cancer, lung cancer, and all types of carcinomas combined.
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Additional analyses revealed that Se supplementation might be associated with a reduced risk of colorectal adenomas, especially among individuals with a low baseline Se level or current smokers.
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The potential ways in which Se acts as an anticancer agent include providing antioxidant protection to DNA, enhancing the detoxification of carcinogens, influencing cell cycle progression, inhibiting tumor cell invasion, and blocking angiogenesis.
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Although limited studies have directly examined Se and its role in anticancer immunity, there is an indication that Se supplementation may enhance immune responses. A study involved human subjects receiving Se supplementation, showing increased performance of lymphocytes involved in antitumor immunity.
How Does Selenium Impact the Aging Immune System?
Aging brings about a gradual decline in various bodily functions, including immune responses. In older individuals, nutritional status significantly influences immune function, and the aging process is associated with cumulative damage to proteins, lipids, and nucleic acids due to oxidative stress. Selenium (Se) plays a crucial role in combating oxidative stress by being incorporated into essential antioxidant selenoenzymes like glutathione peroxidases (GPXs). These enzymes protect against ROS. Selenoproteins, such as thioredoxin reductases and methionine sulfoxide reductase, play key roles in repairing oxidative damage to macromolecules. Leukocytes, vital for immune function, depend on a balance of oxidant and proinflammatory compounds for their activities. As these cells produce reactive oxygen species, maintaining proper Se levels and other antioxidants becomes crucial for sustaining effective immune responses in aging individuals.
Studies on elderly patients' blood cells (PBMC) cultured with both vitamin E and Se showed improved functions, including enhanced chemotaxis and phagocytosis. In a mouse model of premature aging, a multi-nutrient supplement containing Se showed profound effects on leukocyte function, suggesting the utilization of Se by the aging mice. Another study involving healthy aged humans found that Se supplementation alone led to an increase in T cells, particularly CD4+ T cells, and these effects persisted after discontinuation of supplementation.
Further research involving Se supplementation in aged mice showed an increase in plasma IL-6 concentrations, a proinflammatory cytokine, in response to a challenge. While the results are not definitive, they suggest a potential link between Se status and inflammatory processes in the elderly. Overall, maintaining proper Se status is generally considered important for the health of aging individuals, although more research is needed to understand the mechanisms by which Se supplementation may improve immune responses in the elderly.
Conclusion
A lack of selenium has been associated with higher vulnerability to infections and a weakened immune response. Having enough selenium is crucial for immune cells to work properly and for the immune system to function effectively. Selenium is important for a strong immune system. Its antioxidant features, impact on immune cells, and role in defending against viruses all work together to help the body fight off infections and keep the immune system strong. Eating a balanced diet with enough selenium is key to ensuring the immune system works well and maintaining overall health.
