What Vitamins Should Not Be Taken With Selenium?

October 9, 2025 •

4 min read

According to the National Institutes of Health, selenium is a trace mineral vital for human health, playing a key role in metabolism and thyroid function. However, the efficacy of selenium supplements can be compromised by poor timing or combination with certain other nutrients. It's crucial to understand which vitamins should not be taken with selenium to ensure proper absorption and maximum health benefits.

Quick Summary

Taking certain supplements alongside selenium can interfere with its absorption, and one notable interaction occurs with high doses of inorganic vitamin C, which can reduce selenium's bioavailability. Other minerals, particularly zinc, may also compete with selenium for absorption. Timing your supplement intake correctly is a key strategy to avoid these negative interactions and support overall nutrient effectiveness.

Key Points

High-Dose Vitamin C Inhibits Inorganic Selenium: When taken in high amounts, vitamin C can reduce inorganic selenium (like sodium selenite) to a less absorbable form.
Organic vs. Inorganic Selenium: Organic forms of selenium, such as selenomethionine, are generally better absorbed and less affected by vitamin C interactions.
Zinc Competes for Absorption: High doses of zinc can compete with selenium for absorption, so it's best to space them out by at least two hours.
Antioxidant Synergy with Vitamins E and C: Despite the absorption issue with inorganic selenium, selenium works synergistically with vitamins E and C to enhance overall antioxidant effects when timed correctly.
Timing is Crucial: For best results, take selenium supplements with meals to enhance absorption and reduce potential stomach upset.
Consult a Professional for Medications: Selenium can have serious interactions with certain medications, including blood thinners and immunosuppressants, necessitating medical consultation.
Dietary Intake is Preferred: While supplements are an option, ensuring adequate selenium and other nutrient intake through a balanced diet is always recommended.

The Primary Concern: High-Dose Vitamin C

One of the most widely discussed interactions involves vitamin C, particularly when taken in high doses and in conjunction with inorganic forms of selenium, such as sodium selenite. High levels of ascorbic acid (vitamin C) can reduce inorganic selenium to its elemental form. This elemental form is less bioavailable, meaning the body cannot absorb and utilize it effectively. This does not mean these two powerful antioxidants cannot be taken together at all; rather, the timing and form of the supplements are important considerations.

For those taking inorganic selenium supplements, a key strategy is to separate the intake of high-dose vitamin C by at least one to two hours. This separation minimizes the risk of the chemical interaction that reduces selenium's bioavailability. For those consuming organic forms of selenium, such as selenomethionine, this interaction is less of a concern. Organic forms of selenium are more readily absorbed by the body and appear less susceptible to the effects of high-dose vitamin C.

Mineral Competition: Zinc and Selenium

Beyond vitamins, it's also worth noting the competitive relationship between selenium and other minerals, most notably zinc. Both are trace minerals that play crucial roles in numerous bodily functions, including immune response and antioxidant defense. When taken in high doses simultaneously, these two minerals can compete for the same absorption pathways in the digestive system. This can lead to decreased absorption of both minerals, though the effect is often more pronounced with higher doses.

To mitigate this issue, many health experts recommend spacing out the intake of high-dose zinc and selenium supplements by a couple of hours. This allows the body to absorb each mineral more efficiently. For individuals taking a multi-mineral supplement, where the doses are typically lower, this is less of a concern. Always check the dosages in your supplements and consider a staggered schedule if you are taking high-potency, single-nutrient products.

Medications and Other Interactions

It is important to remember that supplements do not exist in a vacuum. Selenium can interact with certain medications and other supplements, and a qualified healthcare professional should always be consulted. For instance, selenium can interact with some immunosuppressants, chemotherapy drugs, and blood-clotting medications. There is also some evidence that selenium may affect cholesterol-lowering statin drugs, particularly when taken alongside other antioxidants like vitamin C and vitamin E.

Synergistic Relationships: The Antioxidant Team

While some interactions are inhibitory, others are synergistic, meaning they work together for a greater effect. Vitamins E and C, despite the high-dose interaction with inorganic selenium, actually work synergistically with selenium in their role as antioxidants. Selenium, through selenoenzymes like glutathione peroxidase, helps to regenerate oxidized vitamin C and E, maximizing the body's overall antioxidant protection. Taking these nutrients together, especially with food, can be highly beneficial for protecting against oxidative stress, provided the timing and dosage considerations mentioned earlier are respected.

The Importance of Timing and Form

In the grand scheme of nutrient absorption, timing and the form of your supplement matter immensely. Taking supplements with meals generally aids absorption and reduces the risk of stomach upset. The presence of food can also help buffer potential negative interactions. For selenium, consuming it with a protein-rich meal can improve absorption, as it is incorporated into selenoproteins. The choice between organic (selenomethionine, found naturally in food) and inorganic (sodium selenite, often in supplements) forms also affects bioavailability and potential interactions, with organic forms being generally better absorbed and less prone to inhibition.

Potential Interactions with Selenium Supplements


Nutrient	Type of Interaction	Risk Level	Mitigation Strategy
High-Dose Vitamin C	Inhibitory (for inorganic selenium)	Moderate	Separate intake by at least 1-2 hours. Take with meals.
Zinc	Competitive	Moderate	Separate intake by at least 2 hours if taking high doses.
Iron	Possible Competitive	Low	Iron and selenium may compete for absorption; separate intake if concerned.
Vitamin E	Synergistic	Beneficial	Works together with selenium as an antioxidant. Safe to take with meals.
Anticoagulant Drugs	Inhibitory (slows blood clotting)	High	Consult a doctor; selenium may increase bleeding risk.
Niacin + Statins	Inhibitory	High	Consult a doctor; selenium and other antioxidants may decrease effectiveness of statins.
Birth Control Pills	Possible Increase in Blood Levels	Low	No clear concern, but consult a doctor if on oral contraceptives.

Conclusion

While selenium is an essential mineral with powerful antioxidant properties, its effectiveness can be hindered by improper co-administration with other supplements. The most critical interaction to be mindful of is with high-dose inorganic vitamin C, which can reduce selenium's bioavailability. Other minerals, such as zinc, may also compete for absorption, requiring staggered timing for optimal intake. However, not all interactions are negative; selenium works synergistically with vitamins C and E to enhance antioxidant protection. By understanding the timing, dosage, and form of your supplements, and consulting a healthcare professional when necessary, you can maximize the benefits of selenium and promote overall wellness. Taking selenium with food, particularly protein-rich meals, is a simple yet effective strategy to boost absorption and minimize potential issues.

Linus Pauling Institute - Selenium Fact Sheet

Frequently Asked Questions

Yes, most multivitamins contain moderate doses of both, and the interaction between selenium and vitamin C is primarily a concern with high, individual doses of inorganic selenium. The presence of food, which is often recommended for taking multivitamins, also helps mitigate any potential issue.

To be safe, particularly if you are taking inorganic selenium, it is best to separate high doses of vitamin C and selenium by at least one to two hours. Taking both supplements with a meal can also aid absorption and minimize interactions.

No, the potential for interaction is largely limited to inorganic selenium supplements. Selenium in whole food sources like Brazil nuts and seafood is in a more bioavailable, organic form and is not significantly affected by vitamin C intake.

Check the ingredients label. Inorganic forms are typically listed as sodium selenite or sodium selenate. Organic forms are often listed as selenomethionine, selenium-enriched yeast, or simply 'selenium (as selenomethionine)'.

Poor absorption, if it leads to deficiency, can result in symptoms such as fatigue, muscle weakness, and in severe cases, thyroid issues and immune dysfunction. However, interactions are often subclinical and don't present obvious symptoms.

If you are taking high, standalone doses of zinc and selenium, it is wise to separate them by a few hours to prevent them from competing for absorption. In a multivitamin, this is generally not necessary.

Yes, selenium and vitamin E work synergistically as antioxidants, enhancing each other's effects. It is perfectly safe to take them together with a meal.