The Role of Selenium in Your Body
Selenium is a trace mineral, meaning your body needs it in only small amounts, yet its impact is widespread. As a component of 25 to 30 proteins in the human body, known as selenoproteins, it performs vital functions ranging from DNA synthesis to protection against oxidative stress. Selenoproteins play key roles in reproduction, thyroid hormone metabolism, and fighting infections.
How Selenium Supports Thyroid Function
The thyroid gland has the body's highest concentration of selenium, where it is used to activate or deactivate thyroid hormones. Without adequate selenium, the body's ability to convert thyroxine ($T_4$) into the more active triiodothyronine ($T_3$) is impaired, potentially leading to hypothyroid symptoms. Selenium also protects the thyroid from the oxidative stress that can occur during hormone production. Studies suggest that selenium supplements may help reduce autoantibodies in individuals with autoimmune thyroid conditions like Hashimoto's thyroiditis and Graves' disease.
Selenium as a Powerful Antioxidant
One of the most important functions of selenium is its role in antioxidant defense. Selenoproteins like glutathione peroxidases and thioredoxin reductases help to neutralize harmful free radicals that can damage cells and DNA. Oxidative stress is linked to chronic conditions such as heart disease, Alzheimer's, and certain cancers. By combating oxidative stress, selenium helps protect your cells and reduce inflammation throughout the body.
Boosting Immune System Function
Selenium's antioxidant properties help reduce inflammation, which enhances immunity. Research has shown that increased blood levels of selenium are associated with a stronger immune response. A deficiency can harm immune cell function and slow the body's response to infection. Selenium also plays a role in the function of immune cells that fight off bacteria and viruses. Some studies suggest that selenium supplements may help strengthen the immune system in people with conditions like HIV, influenza, and hepatitis C.
The Impact on Reproductive Health
Selenium is vital for male fertility and reproduction. It protects against the oxidative damage that can contribute to infertility by ensuring the health and function of sperm. While some studies show that supplements can improve sperm motility in men with a deficiency, more research is needed.
Sources and Supplementation
Getting adequate selenium is typically possible through a balanced diet, as most North American soil is selenium-rich. However, soil content varies by region, so the selenium level in crops can differ.
Selenium-Rich Foods
- Nuts: Brazil nuts are an exceptional source, with just one or two providing the daily recommended amount.
- Seafood: Fish, shellfish, tuna, and sardines are great sources.
- Meat and Poultry: Beef, pork, and turkey are good options.
- Grains: Bread and cereals can contain selenium, depending on the soil where the grains were grown.
- Dairy: Cottage cheese and milk provide selenium.
- Eggs: A reliable source of the mineral.
Comparison of Selenium Supplement Forms
Supplementation can be beneficial for individuals with diagnosed deficiencies or certain health conditions. However, the form of selenium in supplements can vary.
| Feature | Organic Selenium (Selenomethionine, Se-enriched yeast) | Inorganic Selenium (Sodium selenite, Sodium selenate) |
|---|---|---|
| Absorption Rate | Absorbed at a rate of about 90%. | Absorbed at a lower rate, around 50% for selenite. |
| Retention | Has a longer half-life in the body. | Less well-retained once absorbed compared to organic forms. |
| Usage | Often used in supplements for long-term support. | More common in multivitamins, infant formulas, and animal feed. |
| Incorporation | Incorporated non-specifically into proteins in place of methionine, creating a storage pool. | Directly converted to selenocysteine for use in selenoproteins. |
| Blood Concentration | More effectively increases total blood selenium levels. | May increase the activity of certain selenoproteins more effectively, despite lower overall blood levels. |
Risks of Excessive Selenium Intake (Selenosis)
While essential, too much selenium is toxic. The Tolerable Upper Intake Level (UL) for adults is 400 mcg per day. Consuming more than this, especially through supplements, can lead to serious side effects known as selenosis.
Symptoms of selenosis include:
- Garlic odor on the breath
- Hair loss and brittle nails
- Nausea and vomiting
- Fatigue and irritability
- Skin rashes and lesions
In severe cases, very high doses can lead to heart failure, kidney failure, breathing problems, and tremors. It is crucial to consult a healthcare provider before starting selenium supplements to ensure safe and appropriate dosage, especially given that many people already get enough from their diet.
Health Implications of Selenium Levels
An important consideration is the U-shaped curve for selenium's effects on health. Both deficiency and excess can have adverse health consequences. For example, some studies have linked long-term selenium supplementation, particularly at higher doses, with an increased risk of developing type 2 diabetes. In contrast, severe deficiency can lead to heart muscle weakening (Keshan disease) or joint and bone disorders (Kashin-Beck disease), though these are rare in many developed countries.
Conclusion
In conclusion, when you take selenium, your body utilizes this trace mineral primarily to create vital selenoproteins that act as antioxidants, support thyroid function, and boost immune defenses. From protecting your cells from oxidative stress to maintaining optimal metabolism, selenium is a critical component of overall health. However, the key lies in balance. While deficiency can lead to serious health issues, excessive intake is toxic and can cause adverse effects like hair loss and gastrointestinal distress. As with any dietary change, consulting a healthcare professional is recommended before beginning supplementation to ensure you are not consuming too much or too little of this essential mineral.
For more detailed information on selenium's role in the body, visit the NIH Office of Dietary Supplements.
