Selenium is an essential trace mineral that plays a crucial role in numerous bodily functions, including antioxidant defense, thyroid hormone metabolism, and immune system support. The body cannot produce selenium, so adequate intake and proper absorption are necessary to maintain healthy levels. However, a range of factors can cause selenium levels to fall below optimal, leading to deficiency. Understanding these causes is the first step toward correcting the imbalance.
Dietary and Geographic Influences
Low Soil Concentration and Food Sources
The selenium content of food is directly influenced by the soil in which it was grown. While soil in North America is generally selenium-rich, many regions worldwide, including parts of Europe, China, and New Zealand, have naturally low soil selenium levels. As a result, crops and livestock raised in these areas contain significantly less selenium. While extensive food transport can mitigate this in some places, it remains a major factor for local populations.
Vegetarian and Vegan Diets
Individuals following strict vegetarian or vegan diets may have a higher risk of selenium insufficiency, as selenium levels in plant-based foods are often lower than in animal products. Animal sources like seafood, meat, and eggs are typically more concentrated sources of selenium. Without careful dietary planning or supplementation, these eating patterns can contribute to depleted selenium stores.
Medical Conditions That Impair Absorption
Gastrointestinal Disorders
Even with sufficient dietary intake, certain gastrointestinal disorders can impair the body's ability to absorb selenium. Chronic inflammatory conditions that damage the gut lining, such as Crohn's disease, ulcerative colitis, and celiac disease, can severely reduce nutrient absorption, including that of selenium. Chronic diarrhea from various causes can also lead to nutrient loss and increase the risk of deficiency.
Kidney Disease and Dialysis
Patients with chronic kidney disease (CKD) and those undergoing long-term hemodialysis are particularly susceptible to selenium deficiency. Hemodialysis removes micronutrients, including selenium, from the blood during the filtering process. Additionally, the dietary restrictions often required for kidney failure patients can further limit their intake of selenium-rich foods.
Other Chronic Illnesses
Low selenium levels are also associated with other chronic conditions, including HIV, which can cause malabsorption and increased nutritional demands. Autoimmune thyroid diseases, like Hashimoto's thyroiditis, are closely linked to selenium status, and low levels can hamper thyroid function. Critically ill and trauma patients also frequently experience severe selenium depletion due to systemic inflammation and oxidative stress.
Medications and Their Impact on Selenium
Certain medications can interfere with selenium's absorption, metabolism, or increase its excretion, contributing to lower levels over time.
- Cisplatin: A chemotherapy drug that can lower selenium levels.
- Corticosteroids: Such as prednisone, these anti-inflammatory drugs may increase the urinary excretion of selenium.
- Proton Pump Inhibitors (PPIs): Medications like omeprazole may alter the gut environment and hinder selenium absorption.
- Certain Diuretics: Some diuretics can increase the body's excretion of selenium.
- Statins: Long-term use has been observed to potentially reduce selenium-dependent enzyme activity.
Increased Demand and Excretion
Oxidative Stress and Inflammation
When the body experiences heightened oxidative stress, such as during severe infections, inflammation, or trauma, it rapidly depletes its selenium stores. This is because selenium is a critical component of antioxidant enzymes like glutathione peroxidase, which are essential for neutralizing harmful reactive oxygen species. Chronic stress can also lead to increased selenium excretion.
Life Stages and Physical Activity
Certain life stages and lifestyle factors can also increase the body's need for selenium. Pregnancy and lactation increase the maternal demand for selenium to support fetal development and milk production. Excessive physical activity or living in hot climates can increase selenium excretion through sweating, raising dietary needs.
Comparative View: Factors That Deplete vs. Maintain Selenium
| Factor | How it Depletes Selenium | How to Maintain Selenium | Actionable Steps |
|---|---|---|---|
| Dietary Habits | Low intake of selenium-rich foods, reliance on produce from low-selenium soil. | Consuming foods like Brazil nuts, seafood, meats, and eggs. | Diversify diet with selenium-rich sources; consider geographical variations. |
| Medical Conditions | Malabsorption from GI disorders (Crohn's, Celiac) or increased loss (dialysis, HIV). | Medical management of underlying conditions; tailored nutritional support. | Work with a healthcare provider and dietitian for personalized care. |
| Medications | Certain drugs (corticosteroids, PPIs, chemotherapy) can interfere with absorption or increase excretion. | Open communication with your doctor about potential nutrient interactions. | Discuss medication side effects and alternatives with your doctor. |
| Stress & Illness | High oxidative stress and inflammation from infections, trauma, or chronic stress increase selenium utilization. | Managing chronic stress and promptly treating infections. | Incorporate stress-reducing practices; ensure adequate selenium during illness. |
| Gut Microbiota | Intestinal bacteria may compete with the host for limited selenium resources. | Optimizing gut health with probiotics and a balanced diet. | Include fermented foods and fiber to support a healthy microbiome. |
The Role of the Gut Microbiota
Emerging research suggests a complex interplay between the gut microbiome and your selenium status. While a healthy gut microbiome can positively influence selenium absorption and metabolism, some intestinal bacteria can also compete with the host for available selenium. In conditions of low selenium availability, this microbial competition can lead to lower levels of essential selenoproteins in the host. Therefore, gut health is a key determinant of overall selenium status.
Conclusion: Protecting Your Selenium Levels
Depleted selenium levels can result from a multifaceted combination of dietary, medical, and environmental factors. From living in a region with selenium-deficient soil to managing chronic diseases like kidney failure or gastrointestinal disorders, many variables can contribute to low levels. Certain medications, alongside increased bodily demand from oxidative stress, further compound the issue. For most people, consuming a balanced diet rich in selenium sources is sufficient. However, individuals with underlying health issues or who take specific medications may need medical advice to address potential deficiencies. It is important to work with a healthcare provider to accurately assess your levels and determine the best course of action, which may include targeted supplementation. For more information, consult the NIH Office of Dietary Supplements fact sheet on selenium.
