I’ll be the first to admit it, breastmilk is low in iron (0.2–0.5 mg/L low to be precise). I’ll even concede that over the initial months of life, breastfed babies deplete their iron stores. In recent years, this fact has roused a smorgasbord of media outcry, spewing forth headlines such as: “Six months of breastmilk alone is too long and could harm babies” and “Call for U-turn on when to wean”.
It has been a lactivist’s worst nightmare: apparently, evidence surfaced that was unavailable when the WHO made its 6 months exclusive breastfeeding recommendation – and this new evidence wasn’t good. It suggested that breastfed babies had a greater chance of iron deficiency anaemia, “known to be linked to irreversible adverse mental, motor or psychosocial outcomes” (The Guardian 2011). Image stock photos of babies with pale complexions, sunken eyes and dry nails decorated the pages of news sites and blogs around the internet and beyond. Formula feeders lapped it up, hailing it as “good news for once”.
Unsurprisingly, formula companies also joined the media circus, seizing it as an opportunity to exploit the public’s fears.
Now For The Truth:
So has Mother Nature been caught with her panties down? Is iron the one domain where man-made formula can save the day? Well, don’t reach for the bottle (the baby bottle or even the alcohol bottle) just yet. You may be refreshed to hear that rather than being a biological deficit, there is compelling evidence to show that breastfed babies’ lower iron stores are actually an adaptive mechanism – they are a good thing. They are normal. Indeed, they are protective.
The fact of the matter is that many of the bacteria involved in infantile illnesses require iron for growth and replication. By gradually reducing infant iron stores, Mother Nature has limited breastfed babies’ susceptibility to these bacteria. This explains why breastfed babies have a lower frequency and severity of infection.
However, whilst this is awesome news for breastfed babies, it’s a slap in the face for their formula-fed counterparts. For those poor mites, Mother Nature’s adaptive strategy for iron regulation is undermined by the excess dietary iron commonly found in formula. This excess iron promotes the growth of pathogens (read: bad bacteria). This bad bacteria disrupts the synergistic microflora (good bacteria). Result: sick formula fed babies.
In other words, iron deficiency (but not anemia) is a biological strategy for minimizing infection. This mechanism is vitally important for babies because, unlike children or adults, babies shift from a comparatively low risk food (breastmilk) to foods with an increased risk of contamination (solids). With their immature immune systems, babies are at increased risk of contracting novel infections. Thus, by reducing iron stores during infancy, breastfeeding appears to be protective against contracting infections, and, should one nonetheless be contracted, also seems to limit the severity! Nifty stuff!
If we look at this in evolutionary terms and warp ourselves back to prehistoric days, breastfed babies that had lower iron stores at the time of solids introduction were likely to survive on account of having limited iron available for the bad bacteria. Thus, from the perspective of natural selection, breastfed babies’ lower iron stores and their consequently reduced risk of dying from infections, provided positive selection for reduced iron stores. Babies are supposed to have gradually diminishing iron levels. They evolved that way for a healthy purpose! Conversely, the contemporary fortification practices often boasted by formula companies with their fancy “high in iron” claims are, in reality, mismatched to this evolutionary adaptation – they contain an excess of iron. The continued accumulation of iron in formula fed babies combined with the introduction of solids contributes to the increased risks of infection found among formula fed infants (Quinn 2013).
This correlates with past studies which provided evidence that decreased iron intakes appear to be beneficial to infants without increasing the risk of developing iron deficiency anemia. For instance, among babies in Honduras and Sweden randomized to different concentrations of iron supplementation, the babies with reduced iron intake had lower rates of infection and greater head growth than supplemented peers (Domellof et al., 2001).
Formula and Iron: The Risks Examined
If we look at the iron-related risks of formula feeding more closely, the facts can only be described as worrisome. Formula fed babies have a significantly higher likelihood of iron overload – whereby excess iron is absorbed by the baby and accumulates in tissues. This can lead to tissue damage which increases the risk of a wide range of disorders. For example, iron accumulation in neural tissues is linked to the development of Parkinson’s Disease (Youdim et al., 1991), Alhezimer’s (Castellani et al., 2007), and metabolic syndrome (Psyrogiannis et al., 2003). In children specifically, exposure to high levels of dietary iron is associated with decreased linear growth (Dewey et al., 2002), decreased cognitive performance (Lozoff et al.,2012), and altered immune function (Wander et al., 2009).
Looking at the intestines specifically (because many infections in babies begin in the GI tract), the presence of unused iron provides sustenance for bad bacteria to thrive. This reflects recent studies which show marked differences in the composition of the intestinal microbiome between breastfed and formula fed infants.
But wait, aren’t our bodies designed to absorb all the nutrients we need and then expel (read: poop out) the rest? To a certain extent yes, that is true. However I say ‘to a certain extent’ because although a baby’s iron absorption does indeed decrease when iron stores are plentiful, it does not cease completely. Babies have underdeveloped iron uptake regulatory mechanisms and continue to absorb considerable quantities of iron despite sufficient iron stores.
Perhaps even more interesting (or worrying, if you’re a formula feeder), is the fact that iron stores are distributed differently in breastfed babies and formula fed babies. Breastfed babies have normal distribution of hemoglobin, whereas formula fed babies have a skewed distribution (Domellof et al., 2002). Why does this occur? Again, it’s due to the awesomeness of breastmilk. Human milk contains a protein called lactoferrin; this protein plays a very important role in regulating iron uptake. It binds to excess iron, making it harder to absorb. But wait, there’s more! It also binds to the cell membranes of bad bacteria, destructing the cell! So if a breastfed baby has been infected with bad bacteria, the presence of lactoferrin means that they will fight the infection faster. And, as the iron concentrations in their guts are low, they are unable to support large colonies of iron-requiring bad bacteria. Mother Nature is a smart gal after all. The beauty of breastmilk is more comprehensive than commonly thought. Likewise, the risks of formula feeding seem far greater than we had imagined.
What Does This Mean For Weaning Age?
By ‘weaning’ I am referring to the introduction of solid foods into a baby’s diet; this introduction (whether baby-led finger foods or spoon-fed mush) is a physiologically dangerous time for babies. Archaeological records contain numerous examples of deaths occurring around the time of solids introduction (Turner et al., 2007; Wright and Schwarcz, 1998). This is the time period when babies’ exposure to pathogens will increase greatly. The WHO (The World Health Organization – not the 60s English rock band) currently recommends waiting until 6 months before giving solids to your baby. However, baby food manufacturers, greedy for evermore profits, prefer a lower limit, stating “from 4 months” on their packaging. If we consider the science about iron discussed above, when should we be introducing solids to our babies? Recent news reports have cited lower levels of iron in breastmilk as a reason to wean early – earlier than the WHO recommendation.
Who is right? You may ask.
Well you’ve just answered the question yourself, silly! WHO is right. Babies – breast or formula fed – should be offered solids no sooner than 6 months. Now, you may be confused, thinking, ‘Really? Wait until 6 months, even when breastfed babies have lower iron stores?’ Yep, and here’s why: a healthy baby is born with sufficient iron stores, accumulated prenatally, to last them until 6 months. So by the time he reaches this age, his iron stores are low, and as we have discussed, low levels of iron at the time when solids are introduced are beneficial – they reduce the risk of illness (Quinn 2013). Mother Nature has struck a delicate balance between, on one hand, ensuring babies have sufficient iron requirements for growth, whilst on the other hand, being careful not to provide a ready source of iron to pathogenic bacteria. Genius. Then, by the time babies are older and consuming a range of iron-rich foods, they have more mature GI tracts that are more resistant to infection.
So why were the lower iron levels of breastfed babies presented to the public as pathological? Why weren’t they celebrated as the defence-mechanism that Mother Nature designed them to be? Perhaps the science was negatively skewed because of the common misconception that more iron means better health (‘the more – the better’ fallacy); or alternatively, perhaps exploitative formula company marketing is to blame; or, on the other hand, perhaps it was an innocent methodological mistake on the part of researchers who have, until now, failed to look at the evolutionary context – a context that would have revealed why low levels of iron evolved in human milk, and the effect of this on infant physiology.
Or maybe, just maybe, the low levels of iron in breastfed babies has been negatively framed because the study which suggested it was written by an author who had received hefty cash payments from several pharmaceutical companies that make iron supplements. I’ll let you decide.