Can You Take Calcium and Iron Together?
Same day is fine; take separate calcium and iron supplements at different times.
The short answer
Taking calcium and iron together may reduce iron absorption, but studies have not reached a clear conclusion about the long-term effect.
Why it happens
Some single-dose studies found lower iron absorption when calcium was taken at the same time. Studies of everyday diets over longer periods have found mixed results.
What to do
If your calcium and iron are separate supplements, take them at different times of day. If you are treating iron deficiency, follow your doctor, pharmacist, or product instructions.
Who this matters most for
This is most relevant if you take a standalone calcium supplement and a standalone iron supplement, especially if you are correcting an iron deficiency and want absorption to be as reliable as possible. It matters less for people who get calcium mainly from food and take a multivitamin that already combines both minerals in modest amounts, since the studies behind this guidance focused on separate, higher-dose supplements rather than blended products.
What the studies actually showed
The picture is mixed rather than settled. Some single-dose studies found that taking calcium at the same time as iron reduced how much iron was absorbed. But a study that tracked calcium from milk or calcium-fortified foods across a full 4-day diet did not find that it blocked nonheme-iron absorption from the whole diet. That gap between short single-dose experiments and longer whole-diet studies is why the recommendation is cautious rather than absolute: separate the supplements when you can, but do not assume every food containing calcium is working against your iron intake.
When this advice applies
This advice applies mainly to separate calcium and iron supplements. It should not be applied to every food or multivitamin.
Common questions
How many hours apart should calcium and iron be taken?
There is no single required gap. Single-dose studies found lower iron absorption when calcium was taken at the same time, but longer studies of everyday diets found mixed results. If your calcium and iron are separate supplements, the simplest approach is to take them at different times of day rather than in the same dose.
Does milk stop iron absorption?
Not necessarily. A study looking at calcium from milk or calcium-fortified foods over a full 4-day diet did not find that it blocked nonheme-iron absorption from the whole diet. The clearer concern is separate calcium and iron supplements taken in the same dose, not ordinary dairy in meals.
Can I take my multivitamin with calcium and iron in it at once?
Yes. This guidance is about separate calcium and iron supplements, not about every multivitamin or food combination. If you are treating diagnosed iron deficiency, follow your doctor, pharmacist, or product instructions rather than trying to time a multivitamin around it.
References
- Iron — Health Professional Fact SheetNIH Office of Dietary Supplements · 2025
- Calcium from milk or calcium-fortified foods does not inhibit nonheme-iron absorption from a whole diet consumed over a 4-d periodAmerican Journal of Clinical Nutrition / PubMed · 2004
Updated July 31, 2026 · How to use this guidance