Selenium
Selenium is an essential trace mineral required in small amounts for normal human health.
The body incorporates selenium into specialised proteins called selenoproteins, which participate in antioxidant defence, thyroid hormone metabolism, immune function, reproduction and normal cellular processes.
Because selenium requirements are measured in micrograms rather than milligrams, both inadequate and excessive intake are important considerations.
Selenium and Antioxidant Defence
Several selenoproteins form part of the body's antioxidant systems.
These include glutathione peroxidase enzymes, which help manage reactive compounds produced during normal metabolism.
Oxidative stress occurs when the production of reactive molecules exceeds the body's ability to control them.
Selenium therefore contributes to normal cellular protection rather than acting as a simple free-radical scavenger on its own.
Selenium and Thyroid Function
The thyroid contains a relatively high concentration of selenium.
Selenium-dependent enzymes called deiodinases help regulate thyroid hormones, including the conversion of thyroxine (T4) into the more active triiodothyronine (T3).
Other selenium-containing enzymes help protect thyroid tissue from oxidative stress generated during normal hormone production.
This makes selenium important for maintaining normal thyroid function, but selenium supplements are not a treatment for thyroid disease.
People with diagnosed thyroid conditions should consider their total selenium and iodine intake alongside their prescribed treatment.
Selenium and Immune Function
Selenium contributes to normal immune-cell development and activity.
Both inadequate intake and excessive intake can interfere with normal physiology, so the goal is to maintain appropriate selenium status rather than consume as much as possible.
Selenium is commonly paired with nutrients such as vitamin C and zinc in immune-support formulas because each supports different aspects of normal immune and antioxidant function.
Selenium and Reproductive Health
Selenium is also involved in normal reproduction.
Selenoproteins participate in sperm development and function, which helps explain why selenium appears in some men's health and reproductive formulas.
As with other nutrients, additional selenium is unlikely to improve reproductive function when intake is already adequate.
Food Sources of Selenium
Food sources include:
- Seafood
- Meat and poultry
- Eggs
- Dairy products
- Grains and cereals
- Brazil nuts
The selenium content of plant foods can vary substantially depending on the selenium concentration of the soil in which they were grown.
Brazil nuts can contain particularly high and highly variable amounts, so eating large quantities while also taking selenium supplements can make total intake difficult to judge.
Selenium and New Zealand Diets
New Zealand soils are relatively low in selenium in many regions compared with some other countries.
This can influence selenium concentrations in locally produced foods.
However, the modern food supply includes imported foods, seafood, meat and other selenium sources, so living in New Zealand does not automatically mean someone is selenium deficient.
Dietary habits and individual circumstances remain important.
Selenomethionine
Selenomethionine is an organic form of selenium commonly used in supplements.
It is structurally similar to the amino acid methionine and is efficiently absorbed.
The body can incorporate selenomethionine into proteins, creating a pool from which selenium can later contribute to normal selenium metabolism.
How Much Selenium Do We Need?
Adult requirements are relatively small, at around 55 mcg per day.
Because selenium is needed in such small amounts, combining several supplements can quickly increase total intake.
This is particularly relevant when using a dedicated selenium product alongside a multivitamin, mineral formula or prostate supplement.
Too Much Selenium
Excessive selenium intake can cause a condition known as selenosis.
Possible signs include:
- Garlic-like breath
- Metallic taste
- Hair loss
- Brittle nails
- Nausea
- Fatigue
- Neurological symptoms at more serious levels
This is another nutrient where higher intake is not automatically better.
Selenium in O2B Products
At O2B Healthy, selenium is available directly in O2B Selenium Plus, providing 100 mcg of selenium as selenomethionine alongside vitamin C. It is also included in O2B Multi Mineral and O2B Multi Vitamin+ for broader daily nutritional support. O2B ProVision® includes selenium as part of its antioxidant eye-health formula, while O2B Prostate Manager uses selenium within its men's health blend. Selenium is also included in O2B Hyper Zinc and O2B Collagen+, where it contributes antioxidant and cellular support within the wider formulas.