What is iron deficiency? how common is it? who is at risk? and how can you measure it? These are the questions we will deal with in this blog and the next blog will discuss the prevention and treatment of iron deficiency.
Iron is an extremely important mineral for athletes, yet iron deficiencies are not uncommon, particularly in endurance athletes. Iron has several roles in the body including the transport and delivery of oxygen, and energy production at the level of the mitochondria. It is also key for both cognitive and immune function. This highlights why iron is critical for performance, and why an iron deficiency could potentially have detrimental impacts. Symptoms indicative of an iron deficiency include tiredness, a lack of energy, shortness of breath, poor recovery and a reduction in performance (especially if experienced when training load is constant, or during a recovery phase).
Athletes are at a greater risk of being iron deficient in comparison to the general population
Why are athletes more likely to be iron deficient?
Athletes are at a greater risk of being iron deficient in comparison to the general population, especially female athletes, with up to ~35% having an iron deficiency versus ~5% in the general population. Regular exercise can increase the likelihood of an iron deficiency. This is because there is an increased inflammatory response in the body post-exercise, which can decrease the body’s ability to absorb iron for 3-6 hours post-exercise. Inflammation increases levels of the hormone hepcidin, which is key for iron regulation. When hepcidin levels increase, iron transport and absorption decreases (1). There is also potentially increased iron loss from exercise due to hemolysis (the destruction of red blood cells), sweating and gastrointestinal bleeding.
There are particular sub-groups of athletes which are more susceptible to suffering from an iron deficiency, including:
Female athletes, in particular those who regularly menstruate because blood losses are higher.
Athletes who follow a plant-based diet. Plant-based foods contain non-heme iron which isn’t absorbed as well by the body in comparison to animal-based foods (which contain heme iron).
Athletes with low energy intake because iron intake is more likely to be insufficient to support the demands of the body.
Adolescent athletes because this time period is associated with increased iron requirements.
Supplementation may be advised to prevent iron stores from declining any further towards Iron deficiency anaemia where performance can be seriously affected.
What are the signs that you may be iron deficient?
Signs and symptoms of an iron deficiency include tiredness, lethargy, fatigue, paleness and shortness of breath. In athletes, these are even more indicative of a deficiency if these symptoms are experienced when training load if constant (i.e. not progressing), or during a recovery phase. Ideally, reduced iron stores should be detected early before they become depleted in order to reduce the likelihood of any potential effects on performance and/or health. Early detection allows immediate interventions to be put into place (diet/supplementation) to prevent iron stores from declining any further towards IDA (2).
as iron stores become severely depleted, there is evidence to show that this negatively impacts physical performance
During the early stages of an iron deficiency when stores are reduced, but not depleted, the impacts on exercise performance are debated. However, as iron stores become severely depleted, there is evidence to show that this negatively impacts physical performance (3,4). Sub-optimal iron stores are likely to have a greater impact on performance in aerobic based sports due the effect of an iron deficiency on the transport and delivery of oxygen.
How do you test for an iron deficiency?
Athletes should have their iron status assessed by an experienced sports physician. A blood sample is required to test for an iron deficiency. The standardisation prior to measurement is crucial for obtaining a reliable measure of an athlete’s iron status. Considerations should be given to (2):
The time of day – morning is preferable.
Hydration – athletes should be well hydrated.
Prior exercise – 12-24 hours rest from exercise prior to the blood sample is preferable. If exercise is necessary, then only low to moderate intensity exercise should be completed in the 24 hours prior. Muscle-damaging (e.g. eccentric) exercise should not be completed in the 2-3 days prior because this increases inflammation. Some of the proteins measured to identify iron deficiency are so called ‘acute phase proteins’ that respond to stress and inflammation. Therefore, the measurement may reflect the stress or inflammation and not an iron deficiency.
Illness – the athlete should be showing no signs of illness or infection.
To diagnose iron deficiency it is suggested as a minimum that serum ferritin, haemoglobin concentration and transferrin saturation need to be considered.
What are the different levels of iron deficiency?
There are different stages of iron deficiency. The most severe state is iron deficiency anemia (IDA) which results in a host of symptoms, including weakness and fatigue. Two earlier stages can be identified that are precursors to IDA. These are collectively referred to as iron deficiency nonanemia (IDNA). The first and least severe stage of iron deficiency is marked by a fall in serum ferritin resulting from a reduction of total body iron stores, but other iron indices such as haemoglobin remain normal This stage is called nonanemia. The second stage, also non-anemia, is marked by low serum ferritin but also low serum iron or decreased transferrin saturation and increased total iron binding capacity (TIBC). Once iron stores and transport iron have been sufficiently depleted, the body can no longer keep up with the demands of hemoglobin synthesis, and the third and final stage (IDA) results.
Peeling et al. (6) proposed three levels of iron deficiency(see infographic) according to the minimum level of blood markers advised to be measured. These are:
Serum ferritin (μg/L)
Haemoglobin concentration (g/L)
Transferrin saturation (%)
See infographic for the cut-off values used for each stage. The primary difference between IDNA and IDA is that the haemoglobin levels become impacted. Once this occurs, it can start to impact exercise capacity because the body is not able to deliver oxygen around the body as efficiently.
It is a good idea to plan periodic testing of iron status with your sports physician, especially if you are female, vegetarian, have a high training volume and are involved in endurance sports.
In the next blog we will discuss how iron deficiency can be prevented or treated.
Peeling P, Dawson B, Goodman C, Landers G, Trinder D. Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones. Eur J Appl Physiol. 2008;103(4):381-391. doi:10.1007/s00421-008-0726-6
Sim M, Garvican-Lewis LA, Cox GR, et al. Iron considerations for the athlete: a narrative review. Eur J Appl Physiol. 2019;119(7):1463‐1478. doi:10.1007/s00421-019-04157-y
Garvican LA, Lobigs L, Telford R, Fallon K, Gore CJ. Haemoglobin mass in an anaemic female endurance runner before and after iron supplementation. Int J Sports Physiol Perform. 2011;6(1):137-140. doi:10.1123/ijspp.6.1.137
McClung JP, Karl JP, Cable SJ, et al. Randomized, double-blind, placebo-controlled trial of iron supplementation in female soldiers during military training: effects on iron status, physical performance, and mood. Am J Clin Nutr. 2009;90(1):124-131. doi:10.3945/ajcn.2009.27774
Clénin G, Cordes M, Huber A, et al. Iron deficiency in sports - definition, influence on performance and therapy. Swiss Med Wkly. 2015;145:w14196. Published 2015 Oct 29. doi:10.4414/smw.2015.14196
Peeling P, Blee T, Goodman C, Dawson B, Claydon G, Beilby J, Prins A (2007) Effect of iron injections on aerobic-exercise performance of iron-depleted female athletes. Int J Sport Nutr Exerc Metab 17(3):221–231