Thesis Abstract

Abstract
Selenium is an essential trace element for human health, playing a crucial role in antioxidant defense systems and thyroid hormone metabolism. Both selenium deficiency and toxicity can have significant impacts on human health. Selenium deficiency is a global issue, with certain regions being particularly at risk due to low selenium levels in the soil. This deficiency can lead to conditions such as Keshan disease and Kashin-Beck disease, which affect the heart and joints, respectively. In contrast, selenium toxicity can occur from excessive supplementation or environmental exposure, leading to selenosis, which manifests with symptoms such as hair loss, gastrointestinal disturbances, and neurological issues. The effects of selenium deficiency on humans are well-documented and include increased risk of cardiovascular disease, impaired immune function, and cognitive decline. Selenium deficiency has also been linked to male infertility and certain types of cancer. On the other hand, selenium toxicity is less common but can result in serious health consequences. Acute selenium toxicity can cause symptoms such as garlic breath odor, nausea, and neurological abnormalities, while chronic exposure may lead to more severe effects on the liver, kidneys, and nervous system. Understanding the mechanisms underlying selenium toxicity and deficiency is crucial for developing strategies to prevent and treat these conditions. Selenium acts as a double-edged sword, with optimal levels being essential for health, but both excess and deficiency posing risks. The bioavailability of selenium in the diet is influenced by various factors, including soil content, food sources, and genetic variations in selenoproteins. Selenium supplementation is recommended in regions where deficiency is prevalent, but care must be taken to avoid excessive intake. Research on selenium continues to uncover new insights into its role in human health and disease. Recent studies have explored the potential benefits of selenium in cancer prevention, cardiovascular health, and immune function. However, more research is needed to fully understand the optimal selenium status for different populations and to establish safe intake levels. By considering both the risks and benefits of selenium, healthcare professionals can help individuals achieve a balanced selenium status to promote overall health and well-being.

Thesis Overview

INTRODUCTION

1.1.          BACKGROUND INFORMATION

Selenium (Se) is an essential trace element having biological functions of utmost importance for human health. Different from the other (semi) metals, it is incorporated into proteins by a co-translational mechanism as part of the amino acid selenocysteine (SeCys), the 21st amino acid used for protein synthesis in humans, whereas only a few of them have been functionally characterized. Most Se-proteins participate in antioxidant defence and redox state regulation, particularly the families of more specific essential roles, such as iodothyronine deiodinases (DIOs) which are involved in thyroid hormones metabolism, GPx4 which is essential for spermatogenesis, and selenophospathe synthetases 2 (SPS2) participating in Se-protein biosynthesis.

Other Se-proteins may be involved in important biological processes, but their exact mechanism of action is still yet to be fully understood. Despite the scarce knowledge of the precise biochemical functions, a very large number of studies have been carried out in the last two decades showing that insufficient Se levels, and particularly Se-proteins, are associated with several human diseases including cancer, diabetes, cardiovascular and immune system disorders. In most cases, the link lies in the contrast to the oxidative stress that may be booth causing or caused by the disease. In this context, it is important to decipher whether and adequate Se status may contrast the risk factors for health disorders, or Se supplementation may improve the therapy when Se metabolism is altered.

Despite many studies that have suggested a beneficial effect from Se supplementation to general health protection, most of them have remarked that it is limited to general health protection, most of them have remarked that it is limited to the initially inadequate Se status. Conversely, care should be taken when using supplements because excessive Se intake leads to toxic effects, and recent studies have shown that even sub-toxic doses may be negatively impacting, for example by increasing the risk of type 2 diabetes.