I took my first formal nutrition class back in 2014. At the time, I already had a ton of nutrition knowledge, both from on-the-job training and from personal study, but I was beginning to realize I wanted to shift my career from public health into individual nutrition.
As a female and athlete (with digestive issues), I had always struggled with iron, despite eating a fairly high iron diet. At first, I also ate some red meat, and in my nutrition class, we had to complete a three-day food log and perform a nutritional analysis. I was easily meeting the recommended dietary allowance (RDA) for iron. When I asked my instructor about it, a locally practicing registered dietician, she told me, “If you’re consuming the RDA in iron, you should not have low iron status.”
That conversation turned out to be a good jumping off point for wanting to know a whole lot more about nutrition, and nutrient and lifestyle interactions.
If you’re an athlete (male or female), and you’ve ever wondered about what all the hype is on iron, or why you have low iron, or what exercise has to do with iron regulation and absorption, this article is for you.
The Role of Iron and How Iron Deficiency Impacts Athletic Performance
First let’s review what iron does in the body. When we speak about iron, we’re often speaking about it in the context of iron-deficiency anemia. There are many reasons for anemia, not just low iron stores, but iron-deficiency anemia is the most common. Anemia at its most literal means “without blood.” And that’s where we start to talk about iron (though again there are other nutrient depletions that can also cause anemia).
Iron is an essential part of oxygen transport and energy production at a cellular level, and is important for cognitive and immune function (1,2). Hence the reason you feel fatigued when your body is without iron. Note that low energy is also a feature of many nutrient deficiencies since many nutrients are involved in cellular energy production.
For endurance athletes, iron is dually important because it is used for multiple metabolic pathways, including 1) it is used for oxygen transport to the exercising muscle and 2) the production of ATP (energy) is highly reliant on iron.
Common symptoms of compromised iron status include fatigue, lethargy, negative mood, and poor performance during endurance exercise.
A Hormone Called Hepcidin and its Impact on Iron Absorption
Hepcidin is an inflammatory and iron-regulatory hormone that increases for 3 to 6 hours after exercise. This is likely a result of the exercise-induced inflammatory response, and associated increases in an inflammatory cytokine, interleukin-6 (IL-6). Increases in hepcidin result in a decrease in iron absorption as well as decreases in recycling iron from the gut.
So there’s likely a window of time following exercise where the body has altered iron metabolism.
Who is at risk for iron deficiency? The mechanisms that influence iron absorption in athletes
Traditionally, we think of compromised iron status as something that females suffer from. This is because women in their menstruating years generally lose iron through blood loss each month; whereas men should not be losing blood. However, active women are estimated to be twice as likely to present with Iron Deficiency Non-Anemia (stage 2 of iron deficiency) than sedentary, non-active women. Among athletes, we see much higher iron deficiency rates than in the general population with estimates of greater than 50% of female athletes and up to 30% of male athletes having compromised iron stores (1).
Both testosterone and estrogen can influence iron metabolism because they suppress hepcidin (more on this hormone above). When women are exercising at a high training load, this may result in an altered hormonal profile, with gonadotropin-releasing hormone (GnRH), which is a sex-hormone precursor, being suppressed. Consequently, luteinising hormone (LH), follicle stimulating hormone (FSH), and then estrogen will be suppressed. So lower estrogen leads to higher hepcidin (or at least less suppression of hepcidin), and thus more difficulty in absorbing iron.
Likewise, the same result can happen in males with a high training load, with gonadotropin-releasing hormone being suppressed, and consequently suppressed testosterone, and less suppression of hepcidin. In turn, chronically low testosterone in males may be linked to higher hepcidin levels, potentially impairing iron regulation.
Another variable is relative energy deficiency- what I call not eating enough for one’s activity level. Overall low energy availability (LEA) and energy intake may relate to either an overall deficit in dietary iron intake, and/or a dysfunction in iron absorption from the foods that are consumed.
Further, we’re also finding that the makeup of one’s microbiome also affects iron absorption, with iron-deficient individuals lacking lactobacilli species–a key species often cited with good health. Many other bacteria also require iron for growth (3).
Otherwise, vegetarian and vegan / plant-based diets can also impact iron absorption and stores since non-heme plant sources of iron are more difficult to absorb. A big one though, is the general state of your digestion. You have to have good digestive function to assimilate the nutrient.
Finally, some good news: the inflammatory response following exercise can be reduced after long exercise bouts of two hours or longer by consuming carbohydrates during exercise. Eating during exercise decreases the depletion of glycogen stores in the muscle (2), and ingesting carbohydrate during exercise has also been shown to improve the recovery response from long/high intensity efforts.
The Stages of Iron Deficiency:
Stage 1: Iron Deficiency: Iron stores in the bone marrow, liver, and spleen are depleted, indicated by ferritin values less than 35ug/L, Hemoglobin values > 115 g/L, (11.5) and transferrin saturation >16%
Stage 2: Iron-Deficient Non-Anemia: Red blood cell production decreases as the iron supply to the bone marrow is reduced, indicated by ferritin values less than 20ug/L, Hemoglobin >115 g/L (11.5), and transferrin saturation < 16%
Stage 3: Iron Deficiency Anemia: Hemoglobin production falls, resulting in anemia, indicated by ferritin values less than 12 ug/L, Hemoglobin <115 g/L, transferrin saturation less than 16%.
From current research, it appears that depleted iron stores (in stage 1) have minimal or no impact on physical performance, but this is likely particular to you as an individual–some athletes will notice the impact sooner.
What You Are Eating in Your Diet and Iron Status
The timing, amount and source of iron from your diet, in combination with the overall composition of the diet are all important factors to consider when looking at iron status. The most easily absorbed source of iron is heme iron (from meat).
The presence of Vitamin C can enhance non-heme iron absorption, but vitamin C is destroyed by heat (and light), so cooking a vitamin C-rich food into a dish will likely not help much. A couple squeezes of citrus juice at the end of cooking when the food is on your plate can be an effective method to get around this.
Otherwise, polyphenols, phytates, oxalates, calcium, zinc, copper, and vitamin E, which are all part of many nutritious, plant-rich diets and in particular are in whole grains, legumes, leafy greens, and tea and coffee, can decrease the amount of non-heme iron that is absorbed in a meal. Suddenly, your (or my) quinoa salad bowl with nuts, seeds, lentils, spinach and other dark leafy greens, and tahini or almond sauce is not a recipe for a hearty, iron-absorptive meal. Note, these are foods that are frequently on the high-in-iron list! And there are ways to prepare them to make their iron more absorbable, such as soaking, sprouting, fermenting, etc.
Want to Know More?
Within my nutrition practice, I specialize in endurance athletes and digestive imbalances. If you’ve struggled with chronically low iron, or recently have experienced it, I encourage you to reach out to me for more personalized support about how to boost iron around your exercise load.
1). Sim, M., Garvican-Lewis, L.A., Cox, G.R., Govus, A., McKay, A.K.A.,…and Peeling, P. (2019). Iron considerations for the athlete: a narrative review. European Journal of Applied Physiology, 119: 1463-1478. https://doi.org/10.1007/s00421-019-04157-y.
2). McKay, A.K.A., Pyne, D.B., Burke, L.M. and Peeling, P. (2020). Iron Metabolism: Interactions with Energy and Carbohydrate Availability. Nutrients, 12: 3692. https://doi.org/10.3390/nu12123692.
3. Frame, L. (2021, October 7th). Mixed Diet and the Microbiome- Challenges with Complexity. Linus Pauling Institute Diet and Optimum Health Conference, Corvallis, OR, United States.