such as txnrd relocating to the nucleus and activating nf-кb, resulting in further activation of leukocytes and pro-inflammatory cytokine genes. hiv/aids aids appears to involve a slow and progressive decline in levels of selenium in the body. whether this decline in selenium levels is a direct result of the replication of hiv or related more generally to the overall malabsorption of nutrients by aids patients remains debated. observational studies have found an association between decreased selenium levels and poorer outcomes in patients with hiv, though these studies were mostly done prior to the currently effective treatments with highly active antiretroviral therapy (haart). currently there is inadequate evidence to recommend routine selenium supplementation for hiv patients, and further research is recommended. mortality selenium supplementation has no effect on overall mortality. tuberculosis as with other types of supplementation, there is no good evidence selenium supplementation helps in the treatment of tuberculosis. diabetes a meta-analysis of four rcts concluded that there is no support for selenium supplementation for prevention of type 2 diabetes mellitus in caucasians. human reproductive system abnormally high or low levels of dietary selenium can have an adverse effect on sperm quality, with a consequent lowering of fertility. covid-19 during the covid-19 pandemic, some studies tried to correlate between selenium plasma level and severity of covid-19 cases. one study done on 33 patients concluded that low plasma selenium levels were correlated with a high mortality rate among covid-19 patients. however, the median age of deaths in this study was 89 years old; in contrast, survivors' median age was 69 years old, and the study stated that the causality remains unknown. on the other hand, another study revealed that the mean selenium plasma level was within the normal range among all included covid-19 patients; however, the mean selenium plasma level was elevated among severe cases of covid-19. this study concluded that there was a significant elevation of selenium serum level among severe cases compared to non-severe cases of covid-19, and could be correlated with the disease severity. mercury poisoning selenium has a protective effect towards mercury toxicity. mercury binds to selenium with high affinity, so this metal can inhibit selenium-dependent enzymes. however, increased selenium intake can preserve the enzyme activities, reducing the adverse effects caused by mercury exposition. evolution in biology and biosynthetic considerations selenium is incorporated into several prokaryotic selenoprotein families in bacteria, archaea, and eukaryotes as selenocysteine, where selenoprotein peroxiredoxins protect bacterial and eukaryotic cells against oxidative damage. selenoprotein families of gsh-px and the deiodinases of eukaryotic cells seem to have a bacterial phylogenetic origin. the selenocysteine-containing form occurs in species as diverse as green algae, diatoms, sea urchin, fish and chicken. selenium enzymes are involved in utilization of the small reducing molecules glutathione and thioredoxin. trace elements involved in gsh-px and superoxide dismutase enzymes activities, i.e. selenium, vanadium, magnesium, copper, and zinc, may have been lacking in some terrestrial mineral-deficient areas. marine organisms retained and sometimes expanded their seleno-proteomes, whereas the seleno-proteomes of some terrestrial organisms were reduced or completely lost. these findings suggest that aquatic life supports selenium utilization, whereas terrestrial habitats lead to reduced use of this trace element. marine fishes and vertebrate thyroid glands have the highest concentration of selenium and iodine. from about 500 mya, freshwater and terrestrial plants slowly optimized the production of "new" endogenous antioxidants such as ascorbic acid (vitamin c), polyphenols (including flavonoids), tocopherols, etc. a few of these appeared more recently, in the last 50–200 million years, in fruits and flowers of angiosperm plants. in fact, the angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the late jurassic period. about 200 mya, new selenoproteins were developed as mammalian gsh-px enzymes.