Abstract
<jats:p>Selenium is an essential trace element whose biological effects depend strongly on its environmental distribution, chemical form, and bioavailability. Variations in selenium levels in soil and water influence its transfer through the food chain and, consequently, human exposure. In the body, many of selenium’s effects are mediated by selenoproteins, particularly glutathione peroxidases and thioredoxin reductases, which contribute to redox regulation, mitochondrial function, and inflammatory control. However, selenium has a narrow safety range. Both insufficient and excessive intake may disturb redox homeostasis and contribute to neurodegenerative, cardiometabolic, and immune-related disorders. For this reason, the relationship between selenium status and health is often described as U-shaped. In recent years, nano-selenium formulations have attracted attention because they may offer improved bioavailability, more targeted redox modulation, and reduced toxicity compared with conventional selenium compounds. Future research should focus on more accurate assessment of environmental exposure, individualized selenium biomarkers, and safer nanotechnology-based therapeutic strategies.</jats:p>