Why Is Breast Milk So Low in Iron?

When I started feeling concerned about BabyC’s iron status (Does My Baby Get Enough Iron?), I did what most worried, sleep-deprived mamas do – a Google search.  What I found were pages and pages of forums and blog posts full of comments from breastfeeding mothers who couldn’t fathom that their baby wasn’t getting everything she needed from breast milk.  Feed an iron-fortified cereal or give my baby iron drops?  Why?  Isn’t breast milk the perfect food for my baby?  I found many mothers fiercely defending breast milk and accordingly delaying the introduction of complementary foods and shunning the use of any fortified foods or supplements.  I felt compelled to write about this, because I think that in some circles the enthusiasm for breastfeeding has swung a little too far outside of what is actually best and natural for babies.

After digging into the research on infant iron nutrition, I came to the conclusion that breastfed babies really are at higher risk for iron deficiency.  Breastfed babies need to start eating high quality solid foods around 6 months, ideally while continuing to breastfeed, because certain nutrients (including iron, zinc, and vitamin D) are present at low concentrations in breast milk.   The nutrient composition of breast milk is ideal for young infants (< 6 months), but in older infants, breast milk is really no longer the perfect food.  It is an important part of a more complex diet, along with complementary foods.

Here is a very brief summary of infant iron nutrition (I’d like to tackle vitamin D and zinc in separate posts):

  • Most babies are born with enough iron stores to meet their needs for about the first 6 months of life [1].
  • Breast milk contains very little iron (~0.35 mg/liter).  The Institute of Medicine recommends that infants 6-12 months old get 11 mg of iron per day [1].  By this age, most babies’ iron stores have been depleted, so this iron needs to come from complementary foods, in addition to breast milk or formula.  If you try to meet your infant’s iron requirement on breast milk alone, she would have to consume between 4 and 13 liters of breast milk per day, depending on your baby’s efficiency of iron absorption from breast milk (estimates range from 15-50% absorption).  Most exclusively breastfed babies don’t consume much more than 1 liter of milk per day.
  • Iron deficiency during infancy increases the risk of cognitive, motor, and behavioral deficits that may last into the teens, even with iron treatment.  Specific deficits that have been identified include impaired motor development at 18 months [2], mental retardation at 10 years old [3], increased need to repeat a grade, and increased behavioral and attention problems [4].  When I hear parents say that they declined the test for anemia at their baby’s 9 or 12-month check-up, I have to assume that they don’t know how serious iron deficiency can be for their child’s future.
  • Babies that are exclusively breastfed beyond 6 months of age are at higher risk for iron deficiency [5-7] than those fed iron-fortified formula.  This should not be taken as a deficiency of breast milk but rather as an indicator that it is important and natural for babies to start consuming solid foods around 6 months.

In light of these findings, I wondered:

Why would breast milk have evolved to be deficient in iron, putting babies at risk for iron deficiency?

What did the cave babies do before iron supplementation?  This fascinated me. 

We must remember that breast milk evolved over the last 2-2.5 million years to enhance infant survival (and also not put the mother at risk) in the context of the conditions of the time.  In the developed world, there have been major changes in living conditions over just the last several hundred years, and evolution simply doesn’t happen that quickly.  Researchers have proposed 3 hypotheses that could help explain why breast milk is low in iron:

Hypothesis 1.  Babies used to get their iron from soil.  Not too long ago in the history of the world, most people ate and slept on the ground, including babies.  We all know that babies put everything in their mouths, and I doubt if cave babies were any different, especially as they became more mobile around 6 months of age.  Iron in soil can be absorbed by humans [8].  Most other mammals are similarly exposed to soil and also have low concentrations of iron in their breast milk [9].  It is possible that breast milk evolved to have low iron concentrations because babies consumed plenty of iron through their environment (and why drain mom of iron if baby doesn’t need it?).

Banded iron formation specimen from Upper Michigan (Source: Wikimedia Commons)

Hypothesis 2.  Until recently in human history, the umbilical cord was not immediately clamped.  In much of the modern world, it is common practice to clamp and cut the umbilical cord immediately after the birth of a child.  Research has found that waiting just 2-3 minutes after birth before clamping the cord allows up to 50% more blood volume to pulse from the placenta to the newborn [10].  A 2-minute delay has been shown to result in higher total body iron and plasma ferritin (reflecting iron storage) at 6 months of age, equating to about an extra month’s worth of iron stores [11, 12].  Certainly other mammals do not rush to clamp the cord immediately after birth and therefore also get that extra dose of iron to the baby before cutting her off from mom’s supply.

By Ernest F (Own work) [GFDL (www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

Source: Wikimedia Commons, Ernest F

Hypothesis 3.  Breast milk may have evolved to have low iron as a mechanism for protecting infants from infection.  Bacteria require iron to survive and reproduce, and many infections in young infants begin in the GI tract.  What little iron is present in breast milk is bound to an iron-binding protein called lactoferrin.  This limits the amount of free iron in a breastfed baby’s GI tract, which might also limit the growth of harmful bacteria.  Older infants consuming iron-rich foods have more mature GI tracts that would be more resistant to infection.  Although this hypothesis sounds plausible and is explained as if it is fact on sites like kellymom.com, there is actually not much hard data on it.  Human milk inhibits the growth of E. coli in culture, but this effect is lost if enough iron is added to the culture to overwhelm the binding capacity of lactoferrin [13].  However, this has only been shown in culture (in a petri dish) and in animals.  Studies in real live babies have shown mixed results, some finding no effect of iron supplementation on rates of infectious disease and some finding a small effect [14].  A 2002 review of 28 different randomized trials found an overall 11% increase in diarrhea in kids given iron supplements, but this small effect was not associated with iron-fortified foods, only iron drops [15].  In a randomized trial of 4- to 9-month-old infants in Honduras and Sweden, Dewey et al. [16] found that in infants that initially had iron-deficiency anemia, supplementation helped – it reduced the incidence of diarrhea.  However, in infants that were not anemic, iron supplementation increasedtheir incidence of diarrhea.  This implies that too much iron can increase GI infections in infants, providing some support for the hypothesis that low iron in breast milk protects infants from infection.

Beyond these hypotheses, I have found no evidence that babies were breastfed exclusively much longer than 6 months throughout human history.  Most 6-month-old babies are interested in eating because they are interested in putting EVERYTHING in their mouths.  Given every mother’s interest in doing the best thing for her baby, I can imagine that babies have been given some of the best food available throughout human history, and in many cultures, that would be iron-rich meat (maybe initially pre-chewed by mom?).  What about the babies that didn’t get enough iron in their diets?  Before iron supplementation and awareness of the importance of dietary iron, babies probably were more likely to suffer from iron deficiency during the tender transition from breast milk to solid foods, and they probably suffered the consequences.

Thinking about breast milk from an evolutionary perspective helped me to realize that my breastfed baby, who is not raised in the dirt and had her cord clamped immediately after birth (not the plan, but that’s a story for another day), might need a little help getting enough iron in her diet.  If she’ll eat some fortified oatmeal or Cheerios, I’ll take it!  And if her iron tested low, I wouldn’t hesitate to give her an iron supplement to ensure that her brain and body were getting enough iron for normal development.  Of course, it is possible to get enough iron into your baby’s diet without the help of fortified foods, but in practice this can be complicated by a baby’s taste and texture preferences and requires nutritional knowledge and time to prepare iron-rich foods.

For tips on ensuring that your baby gets enough iron, see my post 5 Practical Ways to Increase Iron in Your Baby’s Diet.

REFERENCES

1.  Institute of Medicine, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. 2003, National Academies Press: Washington, D.C.

2.  Sherriff, A., A. Emond, J.C. Bell, and J. Golding. Should infants be screened for anaemia? A prospective study investigating the relation between haemoglobin at 8, 12, and 18 months and development at 18 months. Arch Dis Child. 84(6): p. 480-5. 2001.

3.  Hurtado, E.K., A.H. Claussen, and K.G. Scott. Early childhood anemia and mild or moderate mental retardation. Am J Clin Nutr. 69(1): p. 115-9. 1999.

4.  Lozoff, B., E. Jimenez, J. Hagen, E. Mollen, and A.W. Wolf. Poorer behavioral and developmental outcome more than 10 years after treatment for iron deficiency in infancy. Pediatrics. 105(4): p. E51. 2000.

5.  Meinzen-Derr, J.K., M.L. Guerrero, M. Altaye, H. Ortega-Gallegos, G.M. Ruiz-Palacios, and A.L. Morrow. Risk of infant anemia is associated with exclusive breast-feeding and maternal anemia in a Mexican cohort. J Nutr. 136(2): p. 452-8. 2006.

6.  Hopkins, D., P. Emmett, C. Steer, I. Rogers, S. Noble, and A. Emond. Infant feeding in the second 6 months of life related to iron status: an observational study. Arch Dis Child. 92(10): p. 850-4. 2007.

7.  Calvo, E.B., A.C. Galindo, and N.B. Aspres. Iron status in exclusively breast-fed infants. Pediatrics. 90(3): p. 375-9. 1992.

8.  Hallberg, L. and E. Bjorn-Rasmussen. Measurement of iron absorption from meals contaminated with iron. Am J Clin Nutr. 34(12): p. 2808-15. 1981.

9.  Fomon, S.J. Assessment of growth of formula-fed infants: evolutionary considerations. Pediatrics. 113(2): p. 389-93. 2004.

10.  Dewey, K.G. and C.M. Chaparro. Session 4: Mineral metabolism and body composition iron status of breast-fed infants. Proc Nutr Soc. 66(3): p. 412-22. 2007.

11.  Chaparro, C.M., L.M. Neufeld, G. Tena Alavez, R. Eguia-Liz Cedillo, and K.G. Dewey. Effect of timing of umbilical cord clamping on iron status in Mexican infants: a randomised controlled trial. Lancet. 367(9527): p. 1997-2004. 2006.

12.  Hutton, E.K. and E.S. Hassan. Late vs early clamping of the umbilical cord in full-term neonates: systematic review and meta-analysis of controlled trials. JAMA. 297(11): p. 1241-52. 2007.

13.  Bullen, J.J., H.J. Rogers, and L. Leigh. Iron-binding proteins in milk and resistance to Escherichia coli infection in infants. Br Med J. 1(5792): p. 69-75. 1972.

14.  Baker, R.D. and F.R. Greer. Diagnosis and prevention of iron deficiency and iron-deficiency anemia in infants and young children (0-3 years of age). Pediatrics. 126(5): p. 1040-50. 2010.

15.  Gera, T. and H.P. Sachdev. Effect of iron supplementation on incidence of infectious illness in children: systematic review. BMJ. 325(7373): p. 1142. 2002.

16.  Dewey, K.G., M. Domellof, R.J. Cohen, L. Landa Rivera, O. Hernell, and B. Lonnerdal. Iron supplementation affects growth and morbidity of breast-fed infants: results of a randomized trial in Sweden and Honduras. J Nutr. 132(11): p. 3249-55. 2002.

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45 thoughts on “Why Is Breast Milk So Low in Iron?

  1. Cave babies :)

    Thanks for this post! I’ve wondered about this since your last post on iron, and I’ve worried about it because our 4-month-old daughter’s cord was cut before she was out all the way (also not our plan).

  2. Great post! I knew their must be a reason that breast milk is low in iron, it’s so nice to see all those possibilities that I did not know.

    • Thanks for reading Sharon! I’m finding it really rewarding to read about the science of things that now impact my everyday life! And I’m still thinking about your question about weaning at 6 months – there is just a ton of research to get through, but I hope to post something on it soon.

    • Thanks for reading Kirstin! And I like your vitamin D article too. We didn’t give BabyC a vitamin D supplement when we lived in Arizona because we were both out in the sun quite a bit. I started it when we moved Oregon and agree that there is good evidence for it.

  3. Great article! I love the dirt theory. I think babies (and their parents!) miss out on a lot of good bacteria by not ingesting enough dirt. Not that I’m going to start giving my baby supplements. :) It make me feel like its o.k. to put my baby on the ground when I am out doing something with my older child and not feel like I have to keep her corralled on the blanket. Granted, she gets really dirty and I have to watch out for small rocks and sharp sticks, but I like the idea that it might be good for her, and that I’m not being the lazy mom keeping her entertained so she doesn’t crawl away and entertain herself.

    • Hi Lisa, I think most of the time a little dirt won’t hurt our kids, but I do worry a bit about my daughter ingesting mouthfuls of it at the park. I think about animal poop and the diseases it might carry and the pesticides or herbicides that might be used to keep that grass looking so perfect. And there are choking hazards… Cave babies had to worry about those too:) But I’ve resigned myself that there is only so much I can control as a parent, and yeah, a little dirt will probably do her some good! Thanks so much for reading and for your comment!

  4. Great information. Thank you. I agree that assuming breast milk will supply all the nutrient needs for your baby all the time is a little naive. There will come a time when complementary food is required. However due to very low absorption rates of iron supplements and fortified iron in food products, we choose not to supplement with iron but to start our babies out on iron foods, for example, leafy green, beans, lentils, prunes, raisins, chick peas, and quinoa.

    • Hi Jayda – Thanks for reading my post and for your comment. Iron absorption is very complex and highly variable, and I often see people comment that absorption of fortified foods and supplements are low. This is true, but absorption of all nonheme iron (basically any iron not found in meat or eggs) is very low, ranging from 2-7%. Absorption efficiency of iron from of fortified grains is not any lower than absorption of naturally occurring iron in grains and in fact may even be a little higher. Phytic acid, found in legumes, rice, and grains, inhibits iron absorption, but phytic acid is very low in fortified infant cereals because they are more processed. You can do the math: 1/4 cups of cooked quinoa contains 0.69 mg of iron. Let’s say 6% is actually absorbed in your baby’s GI tract – that will give her 0.04 mg absorbed iron. A similar amount of fortified baby cereal contains about 6 mg iron, giving your baby 0.36 mg absorbed iron (actually meeting about half of her requirement). You can meet your baby’s iron requirement without fortified foods, but I think they are very helpful, particularly for babies that just aren’t eating much solids yet. I hate the highly processed white rice cereal, but you can buy baby cereals made from whole grains, oatmeal, etc. I guess I should write another post on iron absorption. It is so complicated, and there is so much misinformation on this topic online. Thanks again for your comment!

      • I agree iron absorption is complex. There are many variables. Thanks for all the calculations. It does put things into perspective! Is there data on how citrus affects absorption rates? We know it increases absorption but by how much? I soak all our grains/beans before cooking to help breakdown the phytic acid, again I wonder how much this affects to absorption rate of iron? Or cooking n a cast iron pan? I don’t expect you to calculate these figures, I am just adding to the confusion and complexity of iron absorption;) I often recommend to concerned parents to request a simple finger prick and get the child’s iron tested. Once you know the results you can gauge how much you need to worry about iron intake, to supplement or not, etc.

        • I haven’t seen any data on the effects of sprouting grains to increase iron absorption, but I would imagine that would help. Have you ever tried amaranth with your kids? That is the grain with the highest iron content among the ones I looked at. See my post on increasing iron in your baby’s diet for more on vitamin C, which is a great strategy – can double absorption efficiency! I spent a lot of time looking for evidence that cooking in cast iron helps, because I wanted to include it in that post, but I couldn’t find any good research on it. It may help and it won’t hurt, so why not? Blackstrap molasses is also really high in iron, and my baby loves it. It is also high in calcium, which may inhibit iron absorption, but I’m still using a little in oatmeal and baking and hoping for the best. And yes – great advice to get your baby tested for anemia if you aren’t sure she’s getting enough iron. Thanks for the great discussion!

  5. Great discussion! Thanks. Yes, we eat amaranth. I like to include a variety of grains in our diet. Your recommendations in your other article ‘increasing iron..” are the foods in the chart cooked? Just curious. I know that a topic of debate is whether spinach or kale in higher in iron.

    • They are cooked. Thanks for pointing that out – I’ll add it to the table. Follow the link to the USDA nutrient database just below the table if you want to look up more foods. That’s a very helpful resource. Of course, the data there is not always based on a huge number of samples and there will be variation in iron content of foods, but that gets you in the ball park.

  6. Thank you for such a detailed and informative post! Have you addressed Vitamin D already? I have elected not to supplement my son (6 mo) in light of a recent study published in Breastfeeding Medicine that demonstrated sufficient transfer if the mother’s levels were high enough. I take a 2000 IU supplement and had my levels tested, and felt additional supplementation for my son wasn’t necessary, although living in the Upper Midwest and heading into winter I am thinking more about it. I’m always eager to read more on the subject!

    • Hi LeeAnn – Glad you found this post useful! I haven’t written about vitamin D yet, but there is a good post here: http://www.squintmom.com/?p=22. I do give BabyC 400 IU of Vitamin D now. I started it when she was 6 months and we moved from Arizona to Oregon. Plus, I’m supplementing myself now and trying to eat more fish. I’d like to do more research on vitamin D but haven’t had a chance yet, and I definitely trust Squintmom’s word on it.

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    • Sounds like a reasonable hypothesis to me. I can imagine that early hunter-gatherer tribes would value meat very highly, whether or not they had any concept that it contained specific essential compounds, and they would want to share it with their babies! Thanks for sharing this paper. It look like a great source for more info on this topic, and I’m looking forward to reading it.

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  12. Okay, I just found your blog, and wish I had found it 3 years ago with my first kid! I too am a scientist (virologist up at OHSU), and really am grateful for you filtering out the anecdotal vs. the real evidence. Every time one of my friends swears something is true (“Don’t feed your kid cereal! Breastmilk is the perfect food!) I hit up PubMed, but it takes a while to go through all the studies. Anyway, thanks SO much for doing this- especially the sleep-training series.

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  16. babies absorb more iron from breastmilk than any other fortified food/formula. Breastmilk is the perfect food for baby as only baby can use the iron not other gut bacteria. More research needed here full of mis information!

    • As I said in the post, the iron in breast milk is highly available to the baby – it’s really quite impressive. But there is still very little iron there, even if it is well absorbed. And yes, the presence of lactoferrin helps keep that iron unavailable to gut bacteria, which is tremendous. It is perfect for a young infant – just enough iron to meet requirements (in combination with iron stored from pregnancy) without overloading the gut with free iron. But by late infancy, the iron in breast milk is not always sufficient to support a growing baby, and iron deficiency is a serious concern. And a lot of honest research went into this article – I was actually surprised by what I found.

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  18. This is years old, but just because the recommendation is 11 mg per day, doesn’t mean they need 11 mg per day. It is more like 4-5 mg per day. Also, that is taking into account, that iron isn’t easily absorbed, so only a couple of mg at most are actually needed.

    Also, you mentioned the stores of iron. Yes they could be depleted by 6 months (actually 7 months), but that is only if you have fed them virtually no iron. So if they get a few milligrams a day since birth, they will probably be fine, just like the majority of humans in history have been fine.

  19. Me again :)

    So if the baby’s cord was allowed to stop pulsating completely before it was cut, does that indicate that their iron stores could last them beyond 6 mo?

    • Maybe, but how much iron stores your baby has at birth and later in infancy depends on other factors as well. Babies born small or premature have less iron at birth, and for some reason, boys are also at greater risk for iron deficiency. Growth rate also matters – a fast grower is going to be using up more iron. The average 7.5 lb baby with early clamping is thought to “run out” of stored iron around 4 months. Delayed clamping might extend that to around 8 months, probably not much beyond that. (Those calculations are from this paper: http://www.ncbi.nlm.nih.gov/pubmed/17637094)

  20. Thanks for the information. I’ve been very upset recently trying to pump my 9.5 month old full of ferro drops and iron rich foods because her iron stores were 4 and her haemoglobin 10.6. The doctor kept saying for the last 2 months when I asked to check her iron every time I went, “Don’t worry your breastmilk is giving her everything she needs”. But she just didn’t look right to me, her colour was off and she was more fussy and less noisy than usual and she was late crawling, she just didn’t seem to have the strengh. I decided to take her anyway and I was right because her iron was low! She started crawling a week after starting the supplements. I’m convinced it’s linked. I wish all these doctors would take it more seriously. Her iron store was tested at 6.5 months and the doctor could have advised to check again in a couple of months because he would have seen it was running low so I don’t understand why he didn’t. I know her iron wasn’t that low but I can tell you it already affected her negatively so I can confirm how important it is! I’m still so worried about if it caused any permanent damage. :( I followed the advise of not giving infant cereal or grains and that babies don’t need solids until closer to 8 months so I was giving her very little. I even started her on meat at 6 months but obviously the tiny amounts I was giving her weren’t enough.

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  22. I would HIGHLY RECOMMEND testing your child for hereditary hemochromatosis before administering excess iron. If they have two copies of the mutated HFE gene they will not be able to regulate iron uptake and this could have detrimental affects. HHE and autism are closely linked.

  23. I loved this article! I love that you used reputable sources and referenced them as well. I found this while researching iron in breast milk because I’m having difficulties getting my daughter to take to foods. I wonder how much calcium is in breast milk and if that could be a reason for lower iron? Calcium and iron cancel each other out.

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