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Key takeaways
- When taken together, calcium can block iron absorption, making your iron supplement less effective.
- Separate your doses by at least two hours to help your body properly absorb both nutrients. Take iron on an empty stomach (or with vitamin C) and calcium with meals.
- Be very careful about this interaction if you have low iron or are at risk of iron deficiency, such as if you are pregnant, breastfeeding, or following a vegetarian diet.
Calcium supplements can interfere with iron absorption, making it less effective. Taking both supplements at different times of the day can help ensure that your body absorbs both nutrients as intended.
Why calcium and iron don’t mix
Taking iron supplements with calcium may decrease iron absorption, in part because of the way calcium and iron interact in the intestines. When you take them together, calcium can block proteins that carry iron in your bloodstream.
Studies of the short-term interaction between iron and calcium have shown a significant reduction in iron absorption when the two are taken together.
In contrast, long-term studies show no significant changes in overall iron status (such as hemoglobin or serum ferritin) in healthy individuals who increase their calcium intake.
You may need to be more careful about this interaction if you are at higher risk of iron deficiency, especially if you:
- are pregnant or breastfeeding
- Eat a low-iron diet (for example, vegetarian or vegan)
- You have anemia or fatigue due to low iron.
How to time your doses
If you are prescribed to take both calcium and iron supplements, it is best to take them at different times to avoid insufficient iron absorption. Take supplements at least two hours apart for optimal absorption of each.
When to take iron supplements
Follow these tips for taking iron supplements:
When to take calcium supplements
Follow these tips for taking calcium supplements:
- The best time to take calcium supplements is with meals, especially if you are taking a calcium carbonate supplement, to help the body absorb it more efficiently.
- Some multivitamins contain both calcium and iron in the same tablet. However, the quantities are small enough that the interaction effect is negligible.
- If you have a severe deficiency, it’s best to take separate, stronger supplements at different times.
How much iron and calcium do I need?
Calcium and iron are essential minerals for overall health and well-being. Calcium is an essential element for healthy bones and muscles. Iron deficiency can also lead to anemia, general fatigue and developmental problems.
Calcium and iron are both found in a variety of natural and fortified foods. However, many people need to take supplements alongside their diet to meet their needs.
| Recommended daily allowances (RDA) for iron and calcium | |||
|---|---|---|---|
| Adults | Infants, children and adolescents | Food sources | |
| Iron | 8 to 27 milligrams (mg)/day | 0.27-27 mg/day | Meat, beans, lentils, spinach |
| Calcium | 1000 mg-2000 mg/day | 200-1,300 mg/day | Dairy products, tofu, leafy vegetables |
These amounts account for iron and calcium from all sources, including foods and supplements.
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