Does Magnesium Inhibit Iron Absorption? The Truth About Supplement Timing

October 18, 2025 •

4 min read

An estimated 50% of the U.S. population does not consume enough magnesium, leading many to turn to supplements. However, a common concern among those managing mineral deficiencies is whether taking magnesium at the same time as iron will inhibit iron absorption. The answer is nuanced, depending heavily on the form and dose of the magnesium being used.

Quick Summary

The interaction between magnesium and iron depends on dosage and timing. High-dose magnesium oxide can impair iron absorption by changing stomach pH. Other chelated forms are less likely to cause issues, but spacing out intake is a best practice for optimal mineral uptake.

Key Points

Specific Forms Matter: High-dose magnesium oxide, used as an antacid or laxative, is the primary form that can inhibit iron absorption by increasing stomach pH.
Timing Is Key: Spacing out iron and magnesium supplements by at least two hours can effectively prevent absorption interference.
High Doses Increase Competition: When taken simultaneously, large doses of iron and magnesium can compete for shared absorption pathways in the gut.
Choose Chelated Magnesium: Better-absorbed forms like magnesium glycinate or citrate are less likely to cause significant issues with iron absorption than magnesium oxide.
Other Interactions Exist: Calcium, phytates (in grains/legumes), and polyphenols (in coffee/tea) are also known inhibitors of iron absorption.

The Relationship Between Iron and Magnesium

Iron and magnesium are both vital minerals involved in numerous critical bodily functions. Iron is a key component of hemoglobin, the protein in red blood cells that transports oxygen throughout the body, and is essential for energy metabolism and immune function. Magnesium, meanwhile, is involved in over 300 enzymatic reactions, regulating processes from muscle and nerve function to blood sugar control and blood pressure.

When taken as supplements, these minerals can compete for the same absorption pathways in the gut, especially at high doses. The extent of this competition and whether it significantly impacts absorption is primarily influenced by the type and quantity of magnesium taken.

The Role of Magnesium Form in Absorption

The most significant concern regarding magnesium's effect on iron absorption centers on high doses of specific forms, particularly magnesium oxide. This compound is frequently used as a laxative or antacid due to its low bioavailability and ability to increase stomach pH.

How Magnesium Oxide Inhibits Iron Absorption

When high doses of magnesium oxide are consumed, they neutralize stomach acid, which is crucial for converting non-heme iron into a more soluble form that the body can readily absorb. This change in pH reduces the solubility of iron, and the magnesium can also bind with iron to form macromolecular polymers, further hindering absorption. A specific case report documented a woman with iron deficiency anemia refractory to oral iron supplementation due to her overuse of magnesium laxatives. Her condition improved dramatically after stopping the excessive magnesium intake.

Other Forms of Magnesium

Not all magnesium supplements pose the same risk. More bioavailable and better-absorbed forms, such as magnesium citrate, glycinate, and malate, are less likely to significantly interfere with iron absorption when taken at standard doses. They do not drastically alter stomach acid levels in the same way as laxative-dose magnesium oxide. However, to maximize absorption of both minerals, timing is still the most recommended strategy.

Comparison of Magnesium Forms


Magnesium Form	Primary Use	Bioavailability	Likelihood of Inhibiting Iron Absorption
Magnesium Oxide	Laxative, Antacid	Low	High, especially at high doses. Affects stomach pH.
Magnesium Glycinate	Relaxation, Sleep	High	Low, considered a safer choice.
Magnesium Citrate	Laxative, General Supplement	Moderate to High	Low to Moderate. Lower risk than oxide, but high doses may still compete.
Magnesium Malate	Energy, Muscle Health	High	Low.

Best Practices for Taking Iron and Magnesium

For those who need to supplement both iron and magnesium, strategic timing is essential to prevent any potential inhibition and ensure maximum benefit from each mineral. The differing optimal absorption conditions of each mineral provide a clear path for separation.

Take Iron in the Morning: Iron is best absorbed on an empty stomach, about one hour before or two hours after a meal. Taking it in the morning maximizes absorption, especially when paired with Vitamin C to further enhance uptake.
Take Magnesium in the Evening: Magnesium is generally better tolerated when taken with food to minimize the risk of digestive side effects like nausea or diarrhea. Since many people take magnesium for its relaxing properties to aid sleep, an evening dose is ideal.
Ensure a Time Gap: If you cannot separate them by morning and evening, ensure at least a two-hour gap between taking your iron and magnesium supplements.

Other Factors Affecting Iron Absorption

Beyond magnesium, several other dietary and supplemental factors can influence how well your body absorbs iron:

Calcium: High doses of calcium can inhibit both heme and non-heme iron absorption. It is advisable to avoid taking high-calcium foods or supplements near your iron dose.
Phytates: Found in whole grains, legumes, and nuts, phytates can bind to iron and reduce its absorption. Soaking beans and lentils can help reduce phytate content.
Polyphenols: Compounds in coffee and tea, and some fruits and vegetables, can significantly reduce non-heme iron absorption. It's best to consume these beverages between meals rather than with them.
Vitamin C: This is a powerful enhancer of non-heme iron absorption. Taking iron supplements with a glass of orange juice or a Vitamin C supplement can greatly increase bioavailability.
Dietary Protein: The presence of meat, fish, and poultry can enhance non-heme iron absorption.

Conclusion

While high-dose magnesium, particularly in the form of magnesium oxide, can inhibit iron absorption, the interaction is manageable and should not prevent you from supplementing with both essential minerals when needed. By choosing a more bioavailable form of magnesium and strategically timing your supplements—iron in the morning and magnesium in the evening—you can minimize competition and optimize absorption for both. For personalized advice, and especially if treating a diagnosed deficiency, always consult with a healthcare provider to ensure your supplementation strategy is safe and effective. Your health professional can guide you on the right dosages and timing for your specific needs.

Learn more about nutrient interactions here

Best Practices for Nutrient Timing

Separate Supplements: Take iron and magnesium supplements at least two hours apart to prevent absorption competition.
Time for Iron: Take iron supplements in the morning on an empty stomach with a vitamin C source for optimal absorption.
Time for Magnesium: Take magnesium in the evening with food to improve tolerance and leverage its relaxing effects.
Avoid Inhibitors: Do not take iron supplements with calcium-rich foods or drinks, coffee, or tea.
Choose Wisely: Opt for chelated forms of magnesium like glycinate or citrate over magnesium oxide, which can more significantly interfere with iron.
Consult a Professional: Always seek advice from a healthcare provider before starting a new supplement regimen, especially for specific health goals like addressing deficiencies.

Frequently Asked Questions

Yes, it is generally safe to take iron and magnesium supplements together, but it is highly recommended to take them at separate times of the day to minimize competition for absorption.

To optimize absorption, take your iron supplement in the morning on an empty stomach, potentially with some Vitamin C. Take your magnesium supplement in the evening with food to aid digestion and sleep.

Chelated forms of magnesium like magnesium glycinate and magnesium citrate are better absorbed and less likely to significantly interfere with iron absorption compared to magnesium oxide.

Multivitamins that contain both minerals are typically formulated to minimize interaction. However, if you are treating a severe deficiency, separating individual supplements is more effective.

Magnesium consumed through a normal, balanced diet is not considered a clinical problem for iron absorption. The issue primarily arises with high-dose supplements, particularly certain forms like magnesium oxide.

Taking high doses of both at the same time can cause them to compete for absorption, potentially reducing the effectiveness of both supplements. It can also increase the risk of gastrointestinal side effects.

To enhance iron absorption, take your iron supplement with Vitamin C-rich foods or beverages like orange juice. Avoid consuming dairy, coffee, or tea around the time you take your iron.