The Calcium Controversy: Does it Inhibit Iron Absorption or Not?

If you’ve been reading this blog for a while then chances are that you’ve seen a mention or two about iron absorption inhibitors, including calcium. This is a bit of a controversial topic since some say that calcium greatly impacts iron absorption and others say it doesn’t. It can get a little confusing when you’re getting conflicting information, so I thought it would be worth discussing further.

There is some evidence to support the impact of calcium on iron absorption, albeit from short-term studies focused on this interaction with single meals. On the other hand, long-term studies have found that calcium and milk products don’t have any adverse effect on iron absorption.


What’s the Verdict?

Unfortunately this isn’t a simple case of yes or no – hence the controversy! The actual mechanism of the interaction of calcium and iron absorption is not well understood.

The general consensus is that calcium can interfere with iron absorption on a short term basis. According to the Dietary Reference Intakes, while the interaction of calcium and iron is significantly evident in single meals, little effect has been detected in serum ferritin (circulating iron in your blood) concentrations over the long term. In addition, some studies investigating the interaction of iron and dairy products found no detrimental effect on iron absorption.


What Can You Do?

Calcium and dairy products are integral dietary components for both adults and children (and so is iron). While I’ve noted that studies have found calcium to not have a significant inhibiting effect in the long run, if you or your child is dependent on absorbing as much iron as possible, then I recommend avoiding (or at least limiting) taking iron supplements or eating iron-rich meals with calcium, just to be safe. If you’re taking an iron supplement and a calcium supplement, talk to your doctor or pharmacist about possible interactions, dosing, and the best times to take your pills.


If you still have concerns and would like to do all that you can to get the most iron from your diet and supplement, then check out my guide on How to Get the Most out of Your Iron Supplement!

Content and advice provided on The Iron Maiden is for information purposes only and should not serve as a substitute for a licensed health care provider, who is knowledgeable about an individual’s unique health care needs

Print Friendly, PDF & Email
Clip to Evernote

9 thoughts on “The Calcium Controversy: Does it Inhibit Iron Absorption or Not?

  1. Fierce Ninja says:

    Hi there, thank you for this sensible article. I have a quic question. I have a protein bar that has shows Calcium as 12% and Iron as 8%. It has Whey Protein Isolate, Organic Almond butter, Organic Walnuts, Organic Clover Honey, Cinnamon, Chicory Root, Prebiotic fiber. Should I not be taking that bar from a short-term perspective if calcium inhibits iron absorption in short term? Or is the quantity not enough to raise a concern?

    • The Iron Maiden says:

      Hi Fierce Ninja,

      My advice regarding the protein bar is to have the protein bar for the protein alone and not a source of calcium or iron (it’s content is negligible). If necessary supplement with separate iron (preferably polysaccharide iron complex or heme polypeptide as they are better absorbed) and calcium (I prefer calcium citrate or calcium citrate, calcium phosphate combination for better absorption) with Vitamin D. It is recommended that there be a minimum of 2-4 hours between Calcium and Iron supplements.

      Hope that helps!


  2. Bill says:

    I am undergoing a few different investigations with one current diagnoses. my one diagnoses is hyperparathyriodism and during the investigation an iron panel and pituitary hormone screening were completed. So my puitary screen is abnormal and my iron panel revealed hyperferritinemia…
    so hyperparathyroidism is increased PTH and as a direct result hypercalcemia. So question is… can the increase of serum calcium from the hyperparathyroidism affect the results of the iron panel if calcium does effect iron absorption? Ferritin was not crazy high at 440… but binding affect and serum iron were normal. So I am not a large red meat eater but I do have some and have enough iron rich foods from the veggie family which I cut back on… but is there a chance my high level of serum calcium can be causing false or misleading problems?

    • The Iron Maiden says:

      Hi Bill,

      I am truly sorry you are struggling with health issues and having to endure the long process of figuring out what is causing your symptoms. While issues related to parathyroidism are beyond my scope of practice, I can tell you that while ferritin levels are NEVER falsely low (indicating an iron deficiency in its early stages), it can be falsely elevated. If a ferritin level comes back elevated practitioners review other lab values referred to as an “iron panel” (TIBC, Serum Iron, %Transferrin Saturation ). If these are normal range we know that the ferritin level is falsely elevated. Ferritin Levels can be falsely elevated for several reasons including infection, inflammation, chronic illness etc.

      I hope your state of health and wellbeing returns to normal soon.


      • Bill says:

        Thank you for the reply Leona. More deeper looking into things since.. it looks hyperferrentenemia as a redult from inflammation regarding ankylosing spondylitis which i have the HBL7 gene and a working diagnosis and/or early stages of thyroid complications referring back to the hyperparathyroidism and getting closer to a MEN1 diagnosis. Great roll of the dice.. mother has Ankylosing spondylitis and father Neuroendocrine cancer. But it sounds like atleast for now.. liver should be safe.
        Looks like still a long road, but getting currently a good team going.
        Again, thanks for the reply and info. Much appreciated Leona.

  3. Faye Murphy says:

    Hey there! I’m new to the website and I love it, thanks for your work!
    I have a question… is there any information that indicates just how much calcium blocks absorption of iron? I’m pregnant and both are super important for me to consume a lot of right now. So I’m wondering if eating that yogurt in the morning, or cottage cheese at lunch is making my iron supplement pointless? I have to take iron 3x a day, so spacing everything out gets hard to keep up with. Thanks so much! Faye

    • The Iron Maiden says:

      Hi Faye,

      Congratulations on the impending addition to your family! Also, I am happy to see you are actively participating in decisions effecting the health and well-being of yourself and your baby.

      You are right that calcium competes with iron for “bonding sites” on the hemoglobin molecule, although it’s not much of a competition as calcium always wins.

      It is believed that dietary calcium is not as huge a culprit as much as an actual calcium supplement, however, at this point you want to maximize the absorption of both these minerals.

      The weird thing is, if you look at the contents of your prenatal vitamin you will see it contains both Calcium and Iron Salts, the calcium inhibits the conversion and absorption of the iron.

      Understand that you need a minimum of 2 hours between calcium and iron and a minimum of 4 hours between iron doses.

      I want to suggest to you that you discuss with your health care provider the possibility of adding an independent iron supplement. Something that has little if no gastrointestinal tract (GI) symptoms, such as a polysaccharide iron complex or a heme polypeptide complex. Because they have limited GI affects, you could take your first dose in the “wee” hours of the morning when you’re up like almost every pregnant woman I know.

      Hope this helps.

      Congratulations again, and wishing you a very happy, healthy pregnancy and easy delivery. Please let us know if it is a son or daughter.


  4. Vivien says:

    I loved your article! I have iron deficiency, and want to keep my iron levels up after supplements naturally through diet. Most foods rich in iron also are rich in calcium, or have some.
    I am so confused and don’t know what to eat anymore!!!!
    My question is, when a food contains iron and calcium – for example, I’ll eat a 100 grams of Parsley – has 13% Calcium and 34% iron – am I going to absorb this iron?
    Thank you so much!!

    • The Iron Maiden says:

      Hi Vivien,

      Great question.

      Whenever calcium and vegetable source iron are consumed there is an issue, because calcium and non-heme iron compete for the same binding sites.

      The word “compete” is a bit of a misnomer because calcium always wins.

      In the example you give, there is more iron than calcium and one would assume that once all the calcium has found a binding site that the extra iron would be absorbed. This, however, is not 100% true. Before vegetable source iron can be absorbed it must be converted from the type of iron it is into the type of iron your body absorbs. Calcium inhibits this conversion.

      If you are looking to keep your calcium and iron up naturally, look to consume heme irons (those found in meat, chicken, and fish). These iron sources are already the type of iron your body absorbs, therefore, no conversion has to occur. If no conversion has to occur, calcium cannot block that conversion, and the iron is more readily absorbed.

      Keep reading and working towards a better, healthier version of you. Remember to share what you’ve learned as that is the only way to give your knowledge power.


Leave a Reply