What is the optimal timing for taking magnesium and iron supplements in a healthy adult with no significant medical history?

Optimal Timing for Magnesium and Iron Supplements

Take iron in the morning on an empty stomach with water or vitamin C-rich beverage, and take magnesium at a completely separate time—ideally in the evening—because magnesium significantly reduces iron absorption when taken together. 1, 2, 3, 4

Iron Supplement Timing

Morning Administration on Empty Stomach

• Take iron as a single morning dose on an empty stomach (1-2 hours before meals) to maximize absorption. 1, 2, 5
• A single dose of 50-100 mg elemental iron taken in the morning is the optimal strategy, as this timing aligns with lower hepcidin levels that naturally occur earlier in the day. 2, 3
• Afternoon dosing results in 37% lower iron absorption compared to morning dosing due to elevated serum hepcidin levels. 3

Enhance Absorption with Vitamin C

• Taking iron with 250-500 mg vitamin C (such as orange juice) increases absorption by 30% compared to water alone. 2, 3
• Consuming iron with orange juice provides approximately 20 mg more absorbed iron per dose compared to taking it with coffee or breakfast. 3

Critical Avoidances for Iron

• Do not take iron with coffee—it decreases absorption by 54%. 3
• Do not take iron with breakfast, even if it contains vitamin C—this decreases absorption by 66%. 3
• Avoid taking iron with tea, calcium-containing foods or supplements, or meals in general. 1, 2, 6

Magnesium Supplement Timing

Separate from Iron by Several Hours

• Magnesium hydroxide significantly reduces iron absorption when taken together—by approximately 46% when given just 1 hour after iron. 4
• Take magnesium in the evening or at least 4-6 hours away from your morning iron dose to prevent this interaction. 4

Magnesium Dosing Flexibility

• Magnesium supplements can be taken with or without food, as dietary factors have minimal impact on magnesium absorption. 7
• Doses up to 500-1200 mg daily from supplements are well-tolerated without significant gastrointestinal side effects in most adults, despite the outdated 350 mg upper limit. 7

Practical Dosing Schedule

Morning (on empty stomach):

• Iron supplement (50-100 mg elemental iron) with water or vitamin C-rich beverage 1, 2, 3
• Wait 1-2 hours before eating breakfast 2

Evening (at least 6+ hours after iron):

• Magnesium supplement with or without food 7, 4

Integration with Other Supplements

Iron and Folic Acid

• If taking iron-folic acid combination supplements (common in pregnancy or anemia treatment), these can be taken together as a single morning dose. 1
• The complexity of separating multiple supplements negatively impacts adherence more than any theoretical benefit of separation. 1

Calcium Considerations

• If taking calcium supplements, separate these from iron by at least 2-3 hours, as calcium interferes with iron absorption. 1
• Calcium can be taken with magnesium without significant interaction concerns. 1

Monitoring Response

• Expect hemoglobin to increase by at least 10 g/L (1 g/dL) within 2 weeks if iron supplementation is effective. 1, 2, 5
• Failure to achieve this response strongly predicts treatment failure and warrants investigation for malabsorption, continued blood loss, or non-compliance. 1, 2

Common Pitfalls to Avoid

• Do not take multiple iron doses throughout the day—this increases side effects without improving absorption due to hepcidin elevation that persists 24-48 hours after the first dose. 2
• Do not rely on multivitamins as your iron source—they typically contain only 14 mg elemental iron, which is insufficient for treating deficiency. 1, 2
• Do not assume all iron formulations are equally absorbed—ferrous sulfate (200 mg tablet = 65 mg elemental iron) remains the gold standard and most cost-effective option at £1.00 per 28-day supply. 1, 2