Selenium and Immunity
Marina MacDonald, MS, PhD,
6 years ago
15 min read
How this trace mineral supports immune system function
Winter is just around the corner – is your immune system up to snuff? (Or sniffles!) The seasonality of infectious diseases is well established,[1],[2] as any of us who have suffered from the flu can attest. All nutrients are required in greater quantity during an infection, and even mild nutritional deficiencies can render us more susceptible to viruses and bacteria looking for a cozy home.[3],[4]
The white blood cells that mount an immune response to an infection – or to a vaccination – need a constant supply of nutrients to do their jobs.
Immunity is a remarkably sophisticated process by which the body seeks out and destroys harmful viruses and bacteria before they can establish a full-blown infection. However, the white blood cells that mount an immune response to an infection – or to a vaccination – need a constant supply of nutrients to do their jobs.[5],[6],[7] Extensive research suggests that the most important immune system nutrients are vitamins A, C, E, and B6, folic acid, zinc, copper, and selenium.[3],[8]
Selenium is considered a cornerstone of the body’s antioxidant defense system. It serves as an essential cofactor for glutathione peroxidase (GPx), an enzyme that utilizes glutathione to clean up reactive oxygen species that damage immune cells.[9],[10],[11] In states of selenium deficiency, the amount of GPx drops to 10% of normal levels;[12] this impairs the immune response and allows viruses to replicate freely.[13],[14],[15],[16] It’s perhaps not surprising, then, that selenium plays a major role in shielding us against viral infections.[17],[18]
Evidence that selenium protects against viral infections
The story of selenium and antiviral immunity began in China in the 1960s.[19] Geologists investigating the soil conditions of the Keshan county in Northeast China discovered that a serious cardiomyopathy (heart disease) was a result of selenium deficiency.[20] The disease in Keshan residents turned out to be similar to white muscle disease, a heart condition seen in sheep grazing on selenium-deficient soils in the region. Moreover, selenium supplementation was shown to prevent the disease in humans and sheep.[21] The human cardiomyopathy linked to selenium deficiency is so endemic to Keshan county that the disease now bears the name of this area.
The seasonal incidence of Keshan disease suggested that an infectious agent might be involved, and researchers succeeded in isolating a strain of Coxsackie virus from those affected with the disease.[22] In a series of studies akin to a forensic investigation, scientists began to unravel the mechanism behind the effect of selenium.[20],[21] They found that the Coxsackie virus caused more cardiac damage when inoculated into selenium-deficient mice than in selenium-adequate mice.[22] The evidence suggested that insufficient selenium levels caused oxidative stress,[23],[24] which in turn enabled otherwise benign Coxsackie virus strains to mutate to highly pathogenic strains capable of causing heart disease.[25],[26]
“What the results seemed to say was that one could be immersed in a sea of benign Coxsackie virus without any apparent ill effects until one suffered a decline in selenium to the point that the virus would exhibit its cardiovirulent properties.”
As noted by the author of one of these investigative studies: “What the results seemed to say was that one could be immersed in a sea of benign Coxsackie virus without any apparent ill effects until one suffered a decline in selenium to the point that the virus would exhibit its cardiovirulent properties.”[20] In other words, selenium supplementation not only boosted antiviral immunity, but blocked the virus from mutating to a pathogenic form.
Selenium, influenza, and other viral infections
The effect of selenium on immune susceptibility is not limited to Coxsackie virus. Selenium deficiency has been shown to increase one’s susceptibility to influenza and other respiratory viruses, as well as to hepatitis B, hepatitis C, poliovirus, West Nile virus, and hantavirus infections.[27],[28],[29],[30],[31],[32]
Low selenium levels also contribute to the emergence of new and virulent flu strains.[31],[33],[34] As might be expected, children with the highly infectious H1N1 subtype of influenza virus were found to have low blood levels of selenium.[35]
Blood selenium levels have also been shown to be significantly lower in hepatitis C virus (HCV)-positive individuals than in healthy controls.[30] Moreover, the HCV viral load has been shown to be inversely related to selenium levels.[30] Low selenium levels also increase the risk of liver cancer in individuals with a hepatitis B or hepatitis C infection.[36]
Finally, inadequate selenium levels are strongly associated with the prevalence and severity of HIV infection, as discussed below.[37],[38]
HIV and AIDS
The most common nutrient deficiency in HIV-positive individuals is selenium. More than half of HIV-affected individuals are deficient in this mineral.
HIV is the virus responsible for AIDS (Acquired Immune Deficiency Syndrome). HIV impairs immunity by destroying vital cells in the human immune system – specifically CD4-positive T cells, also known as CD4 cells or T helper cells.[17],[39] The CD4 count serves as a snapshot of immune system function in people with HIV, and if the CD4 count drops below 200, a person is diagnosed with AIDS.[40]
The most common nutrient deficiency in HIV-positive individuals is selenium. More than half of HIV-affected individuals are deficient in this mineral.[37],[38],[41],[42] Low serum selenium concentrations are associated with low CD4 counts;[43] a more severe course of disease;[44],[45] an increased risk of cardiomyopathy[46] and of opportunistic infections;[47] and a higher mortality rate.[48],[49],[50],[51]
When HIV-positive patients were supplemented with dietary selenium, however, CD4 counts generally improved.[13],[42],[52],[53] In one placebo-controlled study, the benefits were seen after nine months of daily supplementation with selenium-enriched yeast, provided at a dose of 200 mcg per day.[53]
How much selenium is needed for good health?
Thankfully, the powerful effects of selenium can be achieved with only trace amounts, which is why it’s called a micronutrient!
The U.S. Recommended Dietary Allowance (RDA) of selenium, calculated to meet the needs of most adults, is 55 mcg per day.[54] The main dietary sources of selenium are Brazil nuts, seafood, meat, poultry, fish, eggs, and whole-grain bread.[54] The selenium content of foods varies by geographic region and soil quality.[55],[56],[57] Soils in many regions of the world are deficient, much like the county in which Keshan disease was seen.[58] Importantly, vegan, gluten-free, and low-protein diets provide suboptimal amounts of selenium.[59],[60],[61],[62],[63] Individuals with malabsorption or inflammatory bowel disease may also be deficient in this mineral.[64]
Selenium deficiency is generally thought to be rare in the U.S.,[65],[66],[67] yet a study of Caucasian and African-American women living in Southern U.S. states found that the diets of more than 60% of the population were deficient in selenium.[68] Suboptimal intakes of vitamins C and E, copper, and zinc were also noted. The scientists concluded, “All women in this population reported dietary intakes of antioxidant vitamins and minerals below recommended values, conditions that could contribute to subsequent health risks unless nutrient-dense food choices and antioxidant supplementation are considered in their overall nutritional support.”[68]
Supplemental selenium benefits people with low selenium status, but high levels of selenium can be harmful over the long term,[69],[70],[71] including a possible increased risk of diabetes and amyotrophic lateral sclerosis (ALS).[72] Recent studies suggest that total selenium intakes (from diet and supplementation) greater than 300 mcg per day should be avoided.[73]
Summary
Diets do not always provide adequate levels of selenium. In individuals with low dietary selenium intake and other conditions which may predispose them to have inadequate levels, selenium supplementation may help support a healthy immune system ready to tackle infections – not only in the winter, but throughout the year!
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