Selenium is a trace mineral, meaning the body needs it in small quantities for proper functioning. Its primary function involves antioxidant defense. Antioxidants are substances that help protect cells from damage caused by free radicals, unstable molecules that can harm cells and contribute to aging and disease.
How Selenium Acts as an Antioxidant
Selenium’s antioxidant activity is primarily due to its incorporation into specialized proteins called selenoproteins. A prominent example is the family of glutathione peroxidase (GPx) enzymes, which contain selenium at their active sites. These enzymes neutralize reactive oxygen species (ROS), such as hydrogen peroxide, by converting them into harmless water molecules.
Different forms of GPx are located throughout the body, including the liver, kidneys, red blood cells, and heart, providing widespread protection against oxidative stress. Selenium’s properties make selenoproteins highly efficient at their antioxidant tasks. Beyond GPx, selenium also contributes to the regeneration of other antioxidants, such as vitamins C and E.
Why Selenium Antioxidants Matter for Your Health
Selenium’s antioxidant capabilities are connected to various aspects of health. By neutralizing free radicals and reducing oxidative stress, selenium supports immune function. Selenoproteins help the body fight infections by protecting immune cells from damage and influencing immune responses.
Selenium also plays a role in thyroid function. Selenoproteins are involved in thyroid hormone metabolism, converting inactive thyroid hormone (T4) into its active form (T3), which regulates metabolism and energy production. Adequate selenium levels can also help reduce inflammation in the thyroid gland. Additionally, selenium’s antioxidant action may contribute to cardiovascular health by reducing oxidative damage to blood vessels and influencing inflammation markers.
Where to Find Selenium in Your Diet
Selenium is naturally present in various foods, with concentrations often depending on the selenium content of the soil where the food was grown.
Brazil nuts are an especially rich source, with just a few nuts providing a significant amount of selenium.
Seafood, including fish like tuna, cod, and salmon, as well as shellfish like shrimp and crab, contain notable levels.
Meats such as beef, poultry, and organ meats like kidney and liver are moderate sources.
Eggs, particularly the yolks, contribute to dietary selenium intake.
Whole grains, including brown rice and whole wheat bread, can also provide selenium, though their content may vary.
Understanding Selenium Imbalances
Both too little and too much selenium can have adverse effects on health. Selenium deficiency can lead to increased oxidative stress, weakened immune function, and thyroid issues. A severe form of selenium deficiency, known as Keshan disease, is a type of cardiomyopathy affecting the heart muscle, primarily seen in regions with very low soil selenium levels. Symptoms of Keshan disease include heart failure, cardiac arrhythmias, and fatigue.
Conversely, excessive selenium intake, a condition called selenosis, can also be harmful. Symptoms of selenium toxicity often include hair loss, brittle nails, skin rashes, fatigue, and gastrointestinal disturbances like nausea and diarrhea. A distinctive symptom is a garlic-like odor on the breath. Selenosis is more commonly associated with overconsumption from supplements rather than typical dietary intake.