Timing of iron intake: Tips to maximise absorption

Iron plays an important role in several exercise-relevant processes such as red blood cell production, and energy metabolism, whilst also contributing to our cognitive function, and the body’s immune response. Despite being important, the human body has no innate way to generate its own iron supply, and therefore, we are reliant on dietary iron intake to obtain our daily needs. Interestingly, exercise results in several outcomes that cause us to utilise our iron stores (i.e., red blood cell genesis; adaptation), or to lose iron from the system (i.e., sweating, occult gastrointestinal blood loss). Accordingly, having an adequate iron supply in the diet (or from supplements if needed) is an important consideration for athletes.

Absorption of iron is inefficient

Although an adequate supply of dietary iron is essential, you might be surprised to learn that the absorption of iron from the food we eat is relatively inefficient. For instance, meat eating athletes may only absorb 5-35% of the heme iron found in any given serving of meat, whereas vegetarian athletes may only absorb 2-20% of the non-heme iron found in leafy green vegetables. You can learn more about this here.

Although an adequate supply of dietary iron is essential, the absorption of iron from the food we eat is relatively inefficient

Not only does this tell us that iron absorption is inefficient at the level of the gut, but also that vegetarian athletes must make extra effort to ensure adequate sources of non-heme iron are consumed to make up for the lower relative absorption rate. Notwithstanding, the other foods we consume with our high iron containing meals are also important for us to consider, since we know that the co-ingestion of calcium, tannins (in tea and coffee), and phytates, for instance, can further inhibit the absorption of iron, whereas the addition of Vitamin C (ascorbic acid) to our meal can actually enhance our ability to absorb iron from our food.

Timing of iron consumption

In addition to the type of iron we eat and the foods we consume it with, it is important to note that we must also consider the timing of when we consume our iron in relation to our exercise schedule. The reason why this becomes an important factor is due to the action of the lever-produced hormone known as hepcidin, which is our body’s primary iron regulator. One of the roles of this hormone is to control the amount of iron that passes through the gut and into our system. Generally, increases in hepcidin levels results in a decrease in iron absorption, whereas decreases in hepcidin result in an increase to iron absorption.

We must also consider the timing of when we consume our iron in relation to our exercise schedule

So… if iron is really important, why would the body do this you ask? Good question! It turns out that, although important, too much iron is actually toxic to our body, and so, hepcidin acts to regulate the absorption of iron to ensure we don’t have too much in our system (i.e., more isn’t necessarily better when it comes to iron). To put this in perspective, some of you may have heard of the medical condition hemochromatosis, where patients have extremely high iron levels – well, this condition is characterised by an inability to produce the hepcidin hormone, effectively meaning iron uptake is unregulated and iron toxicity becomes a concern. Given this, it is clearly an evolutionary benefit for us to produce hepcidin as an iron regulator, but why is this relevant to exercise you ask?

Regulation of hepcidin

To answer this question, we must first ask what regulates this hormone? Our current understanding is that factors such as an increase in inflammation or increases in iron act to elevate the hepcidin response, whereas an increase in hypoxia (i.e., altitude) can decrease the hepcidin response. Of course, this latter response is handy when we go to altitude and need more iron in the system to help produce those new red blood cells. However, it is the inflammatory response to training that becomes of interest to iron regulation relevant to exercise.

Influence of exercise

Importantly, we know that exercise results in a transient (temporary) inflammatory response, and when we measure this, we see an increase in the levels of the inflammatory cytokine known as Interleukin-6 (IL-6), which just so happens to be one of the signals to increase hepcidin activity. The research that showed this cytokine/hepcidin link [1] noted that when IL-6 levels were artificially increased, hepcidin levels were elevated 3 hours later.