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Enhancing Endurance: Addressing Iron Deficiency in Athletes

Previously, we learned that ketones have a beneficial impact on Erythropoietin (EPO) production and an enhancement in capillary density. These two physiological factors improve the performance of endurance athletes by enhancing the body's oxygen absorption and utilization. You can find more information on ketones and performance in the blog post here.


The ketone blog post prompted an introduction to the iron profile due to the many questions that resulted from ketone/EPO release/red blood cells. So before we get going, it is important to clarify that this is not medical advice, but rather a summary of information found in textbooks and research papers that most athletes can access at their fingertips. If you have any concerns, please consult your physician.


Questions we will attempt to answer:


1.What is the function of iron?

2. What are the levels and types of iron intake?

3. What are the key aspects of iron deficiency: essential metrics, definition, and progression?

4. What factors lead to iron deficiency in athletes?

5. What are possible treatment options?

6. Summary





1.Function of Iron


Around 5% of the general population typically experiences iron deficiency, whereas in the athletic population, the diagnosis of iron deficiency occurs in 35% of cases (Noakes 2001) (Williams 2005). In other words, athletic or more active individuals seem to be more prone to iron deficiency issues.


Iron is involved in the formation of compounds that transport and utilize oxygen with most of the iron going to making hemoglobin which binds oxygen and carries it from the lungs to the energy factories in the muscle called mitochondria (see previous post here: https://www.thethreshold.coach/single-post/ketones-and-performance-ii-post-exercise-use). Iron is also used in the formation of myoglobin which stores and transports oxygen in the muscle as well as in the formation of ferrochromes which are present in the energy factories mentioned above and are essential for the production of energy currency called ATP (that makes muscles contract).

The remainder of the iron is stored in the tissues in the form of protein compounds called ferritins. Other places where iron is stored (as ferritin) are the spleen, liver, and bone marrow. 30% of iron is stored and 70% is involved in oxygen metabolism


Fig 1. Iron Metabolism in Humans (Williams 2005).


2.Levels and Types of iron intake


Iron is a trace mineral which means it is required in quantities of less than 100mg a day with around 1-1.5mg lost daily from the body. However, because the ability to absorb iron from food tends to be quite low with around 10% bioavailability, it means that the recommended daily allowance is around 10 times the need. See the table below for the Upper Limits of Iron intake by the National Academy of Sciences 2006.


Iron Intake

mg (UL= Upper Limit) (RDA = Recommended Daily Allowance)

Children 


 1-3y

40mg (UL)

4-8y

40mg (UL)

Males, Females


9-13y

40mg (UL) Males 11mg (RDA) Females 15mg (RDA)

14-18y

45mg (UL)

19-70y

45mg (UL) Males 8mg (RDA) Females 18mg (RDA)

>70

45mg (UL)


Iron is further divided into Heme and Nonheme where Heme is found ONLY in animal foods like meat, fish, and chicken and makes up 35-55% of the total iron in that particular food. Nonheme iron is both animals and plants with it making up between 20-70% in animal-based foods, while it makes up 100% in plant-based foods.

Heme is important because of its greater bioavailability with around 10-35% absorbed in the small intestine and only 2-10% for Nonheme.

30g of meat provides around 1mg of heme iron. Consuming Vitamin C with Nonheme iron sources helps absorption because it stops the oxidation of ferrous iron (much more easily absorbed) into the ferric form.




3.Key Aspects of Iron Deficiency: Essential Metrics, Definition, and Progression


Serum Ferritin is a key blood protein that serves as the primary storage protein for iron, alongside hemosiderin. It retains iron until the body requires it, as Serum Iron is a mineral present in red blood cells responsible for transporting oxygen throughout the body.


Hemoglobin (Hb) is the protein found in red blood cells that delivers oxygen to the tissues. Maintaining an adequate level of hemoglobin is necessary to ensure proper oxygenation of the tissues (see fig 2. below).


Hemoglobin
Fig 2. Hemoglobin Molecule with Iron complex

How does the progression of iron depletion and iron depletion anemia occur?

Peeling et al. 2008 gives us the following insights for testing athletes:


  • Stage 1 - Iron Deficiency


It involves bone marrow stores being depleted and a decrease in serum ferritin


  • Stage 2 - Iron Deficiency NON anaemia


Serum Ferritin decreases, less iron in Hemoglobin and less circulating iron.


  • Stage 3 - Iron Deficiency Anemia


Very low serum ferritin and decreased hemoglobin

Symptoms at this stage include paleness, tiredness, and impaired ability to regulate body temperature in a cold environment. The table below gives the levels associated with anemia


Stages of Deficiency

Serum Ferritin (ug/L)

Haemoglobin Concentration (g/L)

Transferrin Saturation (%)

 Stage 1    

 Iron Deficiency

<35

>115

>16





Stage 2 Iron-deficient Non Anaemia 

<20

>115

<16





Stage 3

Iron-Deficient Anaemia 

<12

<115

<16

The table above displays the minimum blood markers recommended for testing iron levels to ensure an accurate diagnosis.


One significant contrast between non-anemia (Stages 1 and 2) and anemia (Stage 3) is the impact on hemoglobin levels. This is crucial because it marks the point at which an athlete's exercise performance starts to suffer due to a significant decrease in the transportation of oxygen throughout the body.



4.Factors Leading to Iron Deficiency in Athletes


  • Increased Iron Requirements: Athletes, especially endurance runners, have higher iron needs due to increased losses in sweat, losses in the gastrointestinal tract, or losses in the urine due to haematuria (blood in the urine) and hemoglobinuria (hemoglobin in the urine) which is caused by f oot strike hemolysis. Foot strike hemolysis can occur during prolonged exercise, particularly in endurance sports like long-distance running. This is the breakdown of red blood cells in the feet due to repetitive impact, leading to iron loss from the body. Sweating has been shown to also contain iron around 0.18-0.20 per liter of sweat. On calculations of heme iron absorption mentioned earlier of 10-35%, it would take around 2-7mg of iron to replace iron loses in sweat alone! (Willams 2005) (Noakes 2001)


  • Vegetarian or Vegan Diets: Plant-based diets typically contain nonheme iron, which is less bioavailable than heme iron found in animal products. Athletes following vegetarian or vegan diets need to be particularly vigilant about their iron intake and absorption. They also lack B12 which plays a crucial role in red blood cell proliferation. Iron absorption inhibitors are certain dietary factors can inhibit iron absorption, such as phytates (found in whole grains and legumes) and polyphenols (found in tea, coffee, and some fruits and vegetables). Consuming these foods alongside iron-rich meals can reduce iron absorption.


  • Menstruation: involves significant iron loss for women, with blood loss being a primary factor. A study conducted on 80 healthy women aged 15-44 measured menstrual blood loss, revealing a median of 37.1 ml per period ranging from 5.4 ml to 169 ml. The average estimated iron loss was approximately 0.55 mg per day (Cheong et al., 1991).

  • Exercise increases inflammation (IL-6) markers that upregulate a hormone called hepcidin which decreases the body's ability to absorb iron for around 3-6 hours post-session. The hormone is also elevated in the afternoon (Peeling et al 2008).


5.Possible treatment options


  • Increasing Iron absorption


Targeting Heme foods (high bioavailability) such as liver, meat, chicken, and fish. Vegans can target foods such as spinach which has around 2-3mg/100g, dates around 1-2mg/100g, beans 1-2mg/100mg, with figs, apricots, hazelnuts, and almonds around 3-4mg/100g, but remember that plant foods are non-heme which only has a low bioavailability. Consuming non-heme foods with Vitamin C has been shown to increase iron absorption (Williams 2005).


  • Supplements


Santiago 2012. suggested that slow-release ferrous sulfate supplements are well-tolerated and have good bioavailability. It is important to take iron supplements in a single dose (or on alternate days) as frequent doses can decrease iron absorption. Vitamin C again helps with iron absorption when taken together. Avoid supplementing iron post-exercise to allow hepcidin hormone concentration to decrease


  • Intravenous Injection


Available via a sports physician and used if normal supplements and dietary intervention do not improve iron status.


6. Summary


  • Athletes tend to be more prone to iron deficiency

  • Heme Iron has a higher bioavailability when being absorbed and is found in meat foods only

  • Non-heme Iron has a lower bioavailability and plant-based food is 100% non-heme.

  • Diagnosing iron deficiency requires knowing Ferritin and Hemoglobin levels

  • Hepcidin is a hormone that decreases iron absorption and is elevated post-exercise, with high inflammation levels in the afternoon

  • Ferrous Sulphate iron supplements have the highest bioavailability




Any help with further questions, discussions, consultations, or coaching? Please don't hesitate to reach out to darrin@thethreshold.coach

@darrinjordaan

@wattfarming


Train Hard and Prosper!


Darrin Jordaan

MSc (Med) Biokinetics WITS

HMS (Hons) Sports Science UP

BK 0016934

CSCS

UCI Level 1 Cycle Certified Coach

IronMan Certified Coach

WADA Coaches of High-Performance Education Program Certified




References


Peeling P, Dawson B, Goodman C, Landers G, Trinder D. Athletic induced iron deficiency: new insights into the role of inflammation, cytokines, and hormones. European Journal Applied Physiology 103(4):381-391. 2008

Sim M, Garvican-Lewis LA, Cox GR, et al. Iron considerations for the athlete: a narrative review. European Journal of Applied Physiology. 119(7):1463-1478. 2019.


Williams, M. 2005. Nutrition for health, fitness and Sport. 7th Edition. New York. McGraw Hill.


Noakes T. Lore Of Running. 4th Edition. Oxford, UK. Oxford University Press. 2001.


Santiago P. Ferrous versus ferric oral iron formulations for the treatment of iron deficiency: a clinical overview. ScientificWorldJournal. 2012: 846824. 2012.


Dietary Reference Intakes: The Essential Guide To Nutrient Requirements. 2006. https://nap.nationalacademies.org/read/11537/chapter/37 Accessed 2024/07/20


Cheong, RL, Kuizon MD, Jajaon RT. Menstrual Blood Loss and Iron Nutrition in Filipino women. Southeast Asian Journal of Tropical Medicine in Public Health. Dec, 22(4): 595-604. 1991

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