The Facts and Fallacies of Iron

The surge of infographics during Iron Awareness Week served as a poignant reminder of the vital role that both updated and correctly interpreted data play.

You might recall our newsletter from last year, in which we scrutinised an infographic on the NZ Iron Week website proclaiming that 8 out of 10 toddlers failed to meet the recommended daily iron intake.

This statistic was drawn from a study published in Public Health Nutrition. However, there was a glaring error in how the results were conveyed. In realityonly 1 out of 5 toddlers or 20% were falling short of their iron requirements.

So, what led to this discrepancy? The prevalence of nutrient inadequacy within a group should always be assessed using the estimated average requirement (EAR). Unfortunately, in the research paper, the authors used the Recommended Dietary Intake (RDI) which is fundamentally wrong in gauging the prevalence of inadequacy. Check out the full story here.

As we continued browsing the internet during Iron Awareness Week, we came across other misleading information.

Interactions of iron and zinc

One website claimed: “Iron deficiency is not necessarily the consequence of low intake but can also be the result of various medical conditions and excess intake of zinc which hinders iron absorption.”  

The first part of this claim is correct: iron deficiency can have many causes, and it’s important to figure out what’s behind it. But the second part is more complicated.

The notion that zinc interferes with the absorption of iron stems from the discovery of a protein called divalent metal transporter 1 (DMT-1) in the late 1990s. This protein was thought to transport both iron and zinc, and therefore create a competition between them. But later studies proved this wrong: iron and zinc use different transport mechanisms.

In fact, zinc may even help with iron absorption, especially when both nutrients are low. Zinc may increase the activity of enzymes that help with iron absorption. So the belief that zinc interferes with iron absorption is too simplistic, and obtaining adequate amounts of both these nutrients is important because zinc deficiency may actually induce iron deficiency.

The real issues tend to arise when these two nutrients are supplemented together. But evidence supports the notion that if supplementation is required, a more effective approach involves providing zinc supplementation first, followed by administration of iron, with a deliberate time gap between the two, could lead to improved responses to iron therapy.

Meat-eater versus plant-eater

Delving into the vast wealth of information available, it's easy to come away with the impression that most vegans should be perpetually fatigued, contending with the looming threat of iron deficiency, while meat enthusiasts should be exuding endless vitality. This perception stems from the fact that vegans consume only non-haem iron sources.

Back-to-the basics: Dietary iron occurs in two forms: haem iron and non-haem iron. Haem iron is only found in animal tissue, while non-haem iron is found in both animal tissue and a variety of plants.

Like for like, haem iron is absorbed much more efficiently, at approximately 25%, compared to the modest 2-3% absorption rate for non-haem iron. Additionally, it's estimated that the bioavailability of iron from a vegetarian diet hovers at around 10%, in contrast to the 18% derived from a mixed diet. Consequently, vegetarians require 1.8 times the iron intake of their omnivorous counterparts. In very strict vegetarian diets, the bioavailability of iron may dip even lower, nearing a 5% overall absorption rate.

But before you rush to the nearest steakhouse, one fact that is often overlooked is that the majority of iron in meat is, in fact, non-haem iron—comprising approximately 60% of the iron content. This means that only around 10% of total daily iron intake in the diet of those consuming meat, comes from haem iron sources. This underscores the notion that the lion's share of dietary iron for most people originates from non-haem sources.

Notably, it's non-haem iron that is susceptible to the influence of other dietary components, which means we all need to consider how we can optimise the absorption of non-haem iron. 

Enhancers versus inhibitors

One of the most potent boosters of iron absorption is vitamin C, aka ascorbic acid. Vitamin C plays a pivotal role by converting oxidised ferric iron into its reduced form, ferrous iron, thereby promoting its absorption. Furthermore, various acids found in fruits and vegetables possess a similar iron-enhancing effect.

Acute studies have demonstrated that incorporating citrus fruits rich in vitamin C into a meal can significantly elevate iron absorption. Notably, this heightened absorption is most apparent when ferritin stores are low, underscoring the body's remarkable capacity to maintain equilibrium.

Animal-derived tissues like beef, chicken, fish, pork, and lamb have also been observed to boost the absorption of non-haem iron. Although the precise mechanisms behind this phenomenon are not fully elucidated, it is suspected that specific constituents of animal tissues, potentially peptides, play a role in this enhanced absorption.

On the flip side, when it comes to inhibitors of iron absorption, there’s an unfortunate paradox. The primary sources of iron in many countries — cereals and cereal products — contain substantial levels of phytic acid. Phytic acidbinds iron, stopping it being absorbed. Other inhibitors include oxalic acid and polyphenols, tannins, antacids, and possibly calcium.

So, when we examine acute studies focused on single meals, we observe a clear pattern: the addition of vitamin C effectively boosts iron absorption, while the incorporation of inhibitors like phytic acid leads to a decline in absorption.

But here's the twist: in longer-term studies spanning several weeks or even months, where participants are consistently exposed to either high levels of enhancers or inhibitors, we see that by the end of these interventions, there appears to be no discernible net effect on iron absorption.

One explanation: It appears that once our iron stores are adequately replenished, further enhancements provide no additional benefits. The human body possesses remarkable adaptive mechanisms, which kick into action when our iron reserves are running low, enabling us to ramp up absorption. This means that there can be a substantial difference in iron absorption from a meal between an individual who is iron deficient and someone with ample iron stores.

Last word: Supplements

There are different types of iron supplements, such as ferrous sulfate, ferrous fumarate, or ferrous bisglycinate. They all have the same goal: to deliver iron to the intestine, where it can be absorbed into the bloodstream.

A typically prescribed supplement has 65 mg of iron. This is equivalent to a week's worth of iron in one go, and far exceeds our capacity to absorb it. As such, some of the iron will pass through the intestine and reach the colon, where there are species of bacteria that specifically target iron. This can cause side effects such as nausea, stomach pain, and black stools directly due to the production of iron sulfide by bacteria.

To avoid these side effects and improve iron absorption, some alternative dosing regimens have been suggested. For example, instead of taking high doses of iron every day, which can overload the transporters that move iron across the intestinal cells and reduce the absorption rate (up to 24 to 36 hours), one can take lower doses or skip some days between doses. This can allow the transporters to recover and increase the absorption rate.

Another factor that affects iron absorption is hepcidin, a hormone that regulates iron levels in the body. High doses of iron can increase hepcidin levels, which can block the release of iron from the cells into the circulation. This can trap iron inside the cells and prevent it from reaching the tissues that need it.

It is interesting to note that hepcidin isn't just induced by high iron intake, it is also increased with inflammation. Even low grade inflammation, a chronic and systemic state of inflammation triggered by obesity, infection, stress, or environmental factors, can increase hepcidin levels leading to what is know as the anaemia of inflammation or the anaemia of chronic disease. 

So, what's the takeaway here? It means that we can all optimise our iron intake by paying attention to the iron rich sources in our diets and making sure we are considering our enhancers and inhibitors. This becomes particularly crucial if we experience persistent low iron levels. Lastly, iron deficiency has many causes, and it’s important to figure out what’s behind it. 

Cool things happening. Keeping track of the innovations in this area that will help improve availability and uptake of iron sources is crucial. This includes adding iron to foods through fortification, increasing the content of iron in foods through biofortification (i.e., plant breeding) or processing foods to boost the absorption of iron.

This is especially relevant as more people are opting for plant-based diets, along with the creation of novel food products and formulations aimed at delivering iron in a more palatable, convenient and affordable way.

We will keep you posted!