Can You Take Selenium and Magnesium Together? A Comprehensive Guide

October 7, 2025 •

4 min read

More than half of the magnesium in the human body is stored in bones. This highlights the mineral's importance and raises questions about optimizing its use with other supplements. So, can you take selenium and magnesium together for enhanced health benefits?

Quick Summary

It is generally safe and often beneficial to take selenium and magnesium together. These essential minerals can work synergistically to enhance antioxidant activity and support healthy bodily functions.

Key Points

Safety First: It is generally considered safe for most people to take selenium and magnesium supplements at the same time, with no major interactions reported.
Synergistic Potential: Research suggests a synergistic relationship, where co-supplementation enhances the activity of antioxidant enzymes and may protect the liver.
Thyroid and Muscle Health: Selenium is crucial for active thyroid hormone conversion, while magnesium is vital for muscle and nerve function.
Upper Limits: Adhering to the Tolerable Upper Intake Level (UL) is critical, especially for selenium (400 mcg/day), to prevent toxicity.
Consult a Professional: Always speak with a healthcare provider before combining supplements to ensure the combination and intake are right for your specific health profile.

The Essential Roles of Selenium and Magnesium

Selenium and magnesium are two essential minerals vital for numerous bodily functions. While they play distinct roles, their combined action can offer synergistic health benefits. Understanding their individual importance is the first step to appreciating why one might consider taking them together.

What is Selenium?

Selenium is a trace element that is nutritionally essential for humans. It is a component of more than two dozen selenoproteins that play critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection. Selenium's primary function is linked to its powerful antioxidant properties, as it is a crucial cofactor for important antioxidant enzymes like glutathione peroxidase.

Key functions of Selenium include:

Thyroid Health: Selenium helps convert thyroid hormone into its active form.
Immune Support: It plays a role in a healthy immune system.
Antioxidant Defense: Protects cells from damage caused by free radicals.
Reproductive Health: Contributes to male fertility.

What is Magnesium?

Magnesium is a major mineral involved in over 300 enzyme systems that regulate diverse biochemical reactions in the body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. More than half of the body's magnesium is stored in the bones, with the rest found in various tissues.

Key functions of Magnesium include:

Muscle and Nerve Function: Essential for proper contraction and relaxation of muscles.
Energy Production: Fuels cellular energy production.
Bone Health: Plays a critical role in the structure and function of bone cells.
Heart Health: Helps maintain a steady heartbeat and normal blood pressure.

The Synergistic Relationship: Can You Take Selenium and Magnesium Together?

Yes, you can generally take selenium and magnesium together, and it may even be beneficial. No significant negative interactions have been found between the two minerals. In fact, research, primarily in animal studies, points towards a synergistic relationship. Co-supplementation has been shown to enhance antioxidant defenses and provide protective effects against issues like hyperlipidemia.

Magnesium is an important component of the body's antioxidant system and may help in the metabolic activation of selenium. One study on rats found that co-supplementation of selenium and magnesium significantly increased the activity of the Se-dependent antioxidant enzyme GSH-Px, suggesting they work together to combat oxidative stress.

Potential Benefits of Taking Selenium and Magnesium Together

Combining these two minerals may offer enhanced support for several areas of health:

Enhanced Antioxidant Activity: Both minerals are components of the body's antioxidant defense system. Magnesium can help restore the activity of antioxidant enzymes, while selenium is a key part of glutathione peroxidase. Together, they may offer more robust protection against cellular damage.
Improved Lipid Metabolism: A 2018 study on rats found that oral co-supplementation of selenium and magnesium had lipid-lowering effects and helped protect the liver against hyperlipidemia induced by a high-fat diet.
Support for Anabolic Hormones: A preclinical study found that a combination of magnesium, zinc, and selenium was more beneficial than individual ingredients alone in raising levels of anabolic hormones like testosterone and IGF-1, which are important for muscle strength, energy, and sexual function.

Selenium vs. Magnesium: A Quick Comparison


Feature	Selenium	Magnesium
Type	Trace Mineral	Major Mineral
Primary Functions	Antioxidant defense, thyroid hormone metabolism, immune function	Muscle & nerve function, energy production, bone health, blood pressure regulation
Adult Daily Needs
Best Food Sources	Brazil nuts, seafood (tuna, sardines), organ meats, eggs	Leafy greens, nuts (almonds), seeds (pumpkin), legumes, whole grains
Tolerable Upper Limit (UL)

How to Take Selenium and Magnesium Safely

When considering any supplement regimen, safety should be the top priority. Adhering to recommended guidelines and choosing bioavailable forms are key.

General Guidelines

Selenium: The Tolerable Upper Intake Level (UL) is 400 mcg daily. Exceeding this can lead to toxicity. Bioavailable forms include selenomethionine and selenium glycinate, which may be better absorbed and gentler on the stomach.
Magnesium: The UL for magnesium from supplements is 350 mg per day; amounts higher than this can cause side effects. Highly bioavailable forms include magnesium glycinate, citrate, and chloride.

Potential Risks and Side Effects

While beneficial, excessive intake of either mineral can be harmful.

Selenium Toxicity (Selenosis): Taking too much selenium (over 400 mcg/day) can cause symptoms like hair and nail loss or brittleness, gastrointestinal issues, fatigue, joint pain, and a garlic-like odor on the breath.
Magnesium Side Effects: The most common side effect of too much supplemental magnesium is diarrhea and abdominal cramping. Very high doses can lead to more serious issues like muscle weakness, low blood pressure, and irregular heartbeat, though this is rare.
Medication Interactions: Magnesium can interfere with the absorption of certain antibiotics (like tetracyclines and fluoroquinolones) and other medications. It's often recommended to take magnesium supplements several hours apart from these drugs.

Conclusion

Evidence suggests that you can safely take selenium and magnesium together, and doing so may provide synergistic benefits, particularly for antioxidant support and metabolic health. There are no known significant adverse interactions between the two when taken at appropriate amounts. However, it is crucial to respect the recommended guidelines for both minerals to prevent toxicity, especially the narrow therapeutic window of selenium. Before beginning any new supplement regimen, including a combination of selenium and magnesium, it is essential to consult with a healthcare provider to ensure it is appropriate for your individual health needs and to discuss proper intake.

For more information on selenium, you can visit the National Institutes of Health (NIH) Selenium Fact Sheet.

Frequently Asked Questions

Both minerals can generally be taken at any time of day, but taking them with food may help prevent potential gastrointestinal upset. Some people prefer taking magnesium in the evening due to its role in muscle relaxation.

When taken within recommended limits, it is unlikely. However, high amounts of magnesium can cause diarrhea and cramping. High amounts of selenium can lead to toxicity with symptoms like hair loss and fatigue.

Consult with a healthcare professional to determine the appropriate daily intake for your individual needs. Referencing general guidelines, it is important not to exceed the Tolerable Upper Intake Level for each mineral without medical advice.

Highly absorbable forms of magnesium like magnesium glycinate or citrate are often recommended as they tend to have fewer gastrointestinal side effects. Selenomethionine is a highly bioavailable form of selenium.

A balanced diet can provide adequate amounts. Selenium is rich in Brazil nuts, seafood, and meat. Magnesium is found in leafy greens, nuts, seeds, and whole grains. However, some individuals may still have deficiencies and require supplementation.

While selenium has few known interactions, magnesium can interfere with the absorption of certain medications, including some antibiotics and bisphosphonates. It is crucial to space out intake by several hours and consult your doctor.

Individuals with kidney disease should be particularly cautious with magnesium supplements, as their bodies may not be able to clear excess amounts. Always consult a healthcare provider before starting any new supplement, especially if you have pre-existing health conditions.