Selenium (Se) is an essential dietary trace element and is required for many functions regarding human health.[1]  Se has structural and enzymatic roles as a constituent of selenoproteins.[2], viagra [3]  Selenium is important for active thyroid hormone1 production and higher Se status reduces the risk of autoimmune thyroid disease.  Selenium is important for the proper functioning of the immune system.[4], information pills [5] Reduced cancer risk has been associated with elevated Se intake and Se is a key nutrient in counteracting the development of virulence as well as inhibiting HIV progression to AIDS.  Low Se status has been associated with cognitive decline, increased risk of mortality and poor immune function.[6]

SELENIUM and Immune Function   

Evidence on the importance of Se to immunity in humans is scarce.  According to Broome et al[7] cellular immune response was improved, virus cleared more rapidly and fewer mutations occurred in its genome, in Se-supplemented subjects.  Natural killer cell activity, increased cytotoxic lymphocyte-mediated tumour cytotoxicity and enhancement of proliferation of activated T cells are all immunostimulant effects from Se supplementation in Se-replete individuals.[8]

Supplementing with 400 mcg Se/d, total T-cell count was significantly increased in a group of elderly subjects. Proliferative response to antigen challenge was increased in elderly Belgian subjects receiving 100 mgc/d for six months.  Increase in cytotoxic-lymphocyte-mediated tumour cytotoxicity by 118% was seen in Se-replete subjects supplemented with Se at 200mcg/d, when compared to placebo.  Increase in NK-cell activity was 82% in the same group.  In a group of elderly subjects receiving Se (100 mcg/day) for 6 months, lymphocyte response to challenge increased by 138% in the Se group, compared with no change in the placebo group.  Se can restore immune response in age-related decline.[9]

SELENIUM and Cognitive Decline  

Lack of Se may lead to irreversible brain injury.[10]  Se is delivered to the brain by selenoprotein P (SEPP1) by binding to a member of the lipoprotein receptor family apoER2.2  SEPP1 is neuroprotective, prevents apoptotic cell death in response to amyloid-b-induced oxidative challenge and enhances neuronal survival.[11]  Evidence from human studies suggests a role for Se in cognitive decline, seizures, PD and coordination.6   The risk of dementia and AD has been linked to Se status in humans.  Subjects with low plasma Se at baseline were at greater risk of cognitive decline in the French EVA[12] cohort of 1166 people aged 60-70 years.  According to Akbaraly et al significant association between the magnitude of plasma Se decrease and cognitive decline was observed over 9 years[13].  Low nail Se concentration in 2000 rural Chinese adults was significantly associated with low cognitive scores.[14]

SELENIUM and Antiviral Effects

Se deficiency has been linked to disease progression of viral infections, or virulence.  Low Se status could lead to myocarditis-inducing mutations in the coxsackie virus which causes Keshan-disease cardiomyopathy. [16],[17],[18],[19],[20],[21]  Human subjects supplemented with Se at 100 mcg/d cleared attenuated poliovirus more quickly and fewer mutations in the viral genome were observed.  HIV-infected subjects commonly suffer from other infections.[22]  In a group of 259 HIV-1 –infected drug users, those with Se <135 mcg/L (plasma levels) had an increased risk (three-fold) of developing mycobacterial disease than those with higher plasma Se.

Evidence reveals benefits from Se supplementation in HIV-infection e.g. marked decrease in hospital admission rates, suppressed progression of HIV-1 viral burden and indirect improvement of CD4+cell count/viral load.[23],[24]   Kupka et al[25] found no effect in a RCT on HIV-viral load or on CD4+cell count in Tanzanian pregnant women, when supplemented with 200 mcg Se/d (reduction on child mortality was observed).  Reduced risk of immune decline and morbidity was observed with a single daily supplement containing multivitamins and 200 mcg Se in HIV-infected adults from Botswana.[26]

SELENIUM and Autoimmune Thyroid Function

The thyroid gland has a high Se concentration and Se is important for thyroid function.[27]  Se was significantly associated with less eye involvement, slower progression of Graves- orbitopathy and improved quality of life.[28]

Autoimmune thyroiditis (AIT) affects females (>15% >60yr) and males (2% [irrespective of age]).[29]  Supplementation of AIT patients with Se (80 or 200 mcg/d) decreased inflammation and thyroid peroxidase autoantibody (TPO-Ab) concentrations in 7 out of 11 RCT.29,[30]    Improved mood and/or general well being  was also reported.

Findings from Santos et al[31] support the existence of a link between selenoprotein S gene (SEPS1) promotor genetic variation and Hashimoto’s thyroiditis (HT) risk/susceptibility.

Positive TPO-Ab measurements in pregnancy can be associated with post-partum thyroid dysfunction and permanent hypothyroidism.6  In women receiving 200 mcg Se/d (as selenomethionine), post-partum thyroid disease and permanent hypothyroidism were significantly reduced as thyroid inflammatory activity fell[32]

SELENIUM and Cancer

Evidence from prospective studies exist on beneficial effects of Se on the risk of prostate[33],[34],[35],[36],[37], lung[38], bladder[39] and colorectal cancers.  In a dose-response meta-analysis[40] the risk of total- and advanced prostate cancer (PCa) decreased with increasing plasma/serum Se up to 170 ng/mL.  Reduction in PCa was observed with a toenail Se concentration between 0.85 and 0.94 mcg/g, in three high-quality studies of toenail Se and cancer risk.  Population with low baseline serum Se and high risk for cancer benefit from Se supplementation[41],[42]   Duffield-Lillico et al[43] reported a significant reduction in cancer mortality, cancer incidence and PCa incidence in the NPC trial.  Greater effect has been reported on advanced PCa (p=0.03) than on the local disease (P=0.02) with supplemental dietary Se.[44]  In the SELECT[45] trial no effect was found on PCa risk from Se or Se with vitamin E.[46]   Baseline Se status was higher than in the NPC trial in the subjects with no benefit from Se supplementation (Se-methionine), only 1% of the cases were non-localized and only one PCa death occurred.  Se supplementation increased the risk of high-grade PCa in men with higher Se status but had no effect in men with low Se status.[47]  Geybels et al[48] reported significantly reduced risk of advanced PCa with increasing Se status (p=0.001).


Selenium is an essential dietary trace element.  Healthy selenium status is important for immune function, for preventing virulence and for preventing cancer.  Selenium is important for the brain and healthy cognition.

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3 Kryukov GV, Castellano S, Novoselov SV, Lobanov AV, Omid Zehtab, et al. Characterization of mammalian selenoproteines. Science 2003;300(5624):1439-1443.

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9 Peretz A, Neve J, Desmedt J, Duchateau J, Dramaix M, Famaey J. Lymphocyte response is enhanced by supplementation of elderly subjects with selenium-enriched yeast. Am J Clin Nutr 1991;53(5):1323-1328.

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23 Burbano X, Miguez-Burano MJ, McCollister K, et al. Impact of a selenium chemoprevention clinical trial on hospital admissions of HIV-infected participants. HIV Clin Trials 2002;3:483-91.

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