Iron

Iron Requirements

Role of Iron- Specific to Exercise 

Iron is key to endurance performance because it is an essential component of hemoglobin (Hgb) a protein in the red blood cells that transports oxygen from the lungs to the tissues and removes CO2 from the tissues and carries it back to the lungs.   Iron also plays a critical role in energy production, taking part in oxidation/ reduction reactions in the electron transport chain- the final step in the process of producing Adenosine Triphosphate (ATP) which is what supplies the energy for muscle contraction.  Finally, iron (describe myoglobin).  

Given the important roles of iron in oxidative metabolism, oxygen transport, storage and utilization it is no surprise that a deficiency of iron (also referred to as iron deficiency anemia) negatively impacts endurance performance.  Studies have documented decreases in VO2max of up to 50% . In addition to decreasing aerobic capacity, iron deficiency anemia decreases endurance capacity or time to exhaustion, which is the duration in which a given intensity or power can be maintained before it declines. 

Iron Deficiency Stages and Signs of Anemia

Iron deficiency has 3 stages: 

1. iron depletion

2. Iron deficiency without anemia

3. Iron deficiency anemia

The first 2 stages can develop over a long period of time. Unfortunately, signs/ symptoms do not appear in the 1st stage and often not until stage 3- iron deficiency anemia. That is why it is important that athletes, especially female athletes, have at least biannual lab work to monitor iron storage and transport (CBC and serum ferritin); this will allow for early detection of iron depletion or dropping iron stores, indicating that intake is not sufficiently replenishing iron loss. 

Signs of Iron deficiency Anemia: 

• Decreased performance

• Inability to finish long or intense training sessions

• Inability to finish training sessions as well as localized muscle weakness 

• Extreme fatigue

• Inability to concentrate 

• Cold intolerance, cold hand and feet

• Headaches, dizziness, or lightheadedness 

• General paleness

Risk Factors for Inadequate Iron Intake 

Endurance runners are at a heightened risk of iron deficiency for multiple reasons, including higher iron losses, and high risk of negative energy balance -from low energy intake or restriction (and therefore subsequent low iron intake)- which commonly occurs in distance runners.  Additional factors that further increase risk include: high training load (i.e., high intensity and/or duration of training sessions), being vegetarian or vegan, being female, and high dietary intakes of iron inhibitors (calcium in dairy foods, zinc supplementation, phytates in tea and coffee, insoluble fibers, etc). Below will further discuss each of the mentioned risk factors. 

• High training volume  

• Energy restriction

• Vegan/vegetarian eating patterns

• Intake of iron inhibitors 

• Female gender

Running leads to heightened iron losses through multiple avenues. As a result of the inflammation caused by high training loads, the body releases a hormone called hepcidin that impacts the absorption and transport, and recycling of iron, resulting in increased excretion. Iron is lost through foot strike hemolysis in which ruptured blood vessels damage red blood cells - resulting in iron losses. Additional losses may occur through gastrointestinal bleeding from GI inflammation, and increased losses through sweat, urine and feces.

Endurance running is often considered a weight sensitive sport due to the perceived notion that a lean body type and/or lower weight will lead to performance enhancements. Aside from that unfortunate belief being false, it can lead to restricted eating behaviors- which increase the athlete’s risk of falling short on essential nutrient needs, including iron. 

Iron from animal foods is more bioavailable than iron in plant-based foods due to the type of iron present in each. Heme iron present in meat, fish, and poultry is readily absorbed and it’s bioavailability ranges from 15-35%. Whereas non-heme iron’s bioavailability is much lower, ranging from 2-20%. 

In addition to non-heme iron being less efficiently absorbed and utilized by the body, food components present in plant based foods further inhibit absorption by combining with the mineral and excreting it prior to absorption. Examples of this include insoluble fibers, phytates, oxalates, and tannins present in certain plant foods, and caffeinated beverages. Calcium and zinc compete for iron absorption, so high dairy intake or supplements of either of these minerals can negatively impact iron absorption. 

On average, it is estimated that for every 1,000 kcals consumed, iron intake is ~6-7mg. As you can see in the DRI chart listed above, it is fairly easy for the majority of males to meet their daily iron requirements considering their average energy needs are higher and their iron needs lower, compared to females. Females have increased iron needs due to menstruation. It is easy to see how females can easily fall short on their daily iron needs. Just consider that, based on the average iron intake mentioned above, a female consuming a 2,000 kcal/day diet would still fall short on meeting her needs. The deficit would be further exacerbated if the other risk factors mentioned above are also present (increased training, vegetarian, restricted intake, endurance runner, etc). 

Dietary Sources of Iron

Heme Iron (best absorbed)

• Shellfish

• Beef liver

• Beef 

• Organ meat

• Other meats and fish

Non-heme Iron (less bioavailable)

• Most soy products

• Lentils 

• Beans 

• Cashews and other nuts

• Dark green vegetables

• Pumpkin seeds and other seeds 

• Quinoa

• Teff 

• Dark chocolate 

• Eggs

Tips for Maximizing Iron Absorption

The list above is not exhaustive, but provides some idea of foods containing a moderate-high amount of iron. Since heme iron is more bioavailable, it’s wise to consume heme iron sources at least 3 times per week. Additionally, it’s important to focus on factors impacting absorption, especially when consuming non-heme iron sources. Below are lists of food components that either enhance or inhibit iron absorption. 

Enhancers 

• Vitamin C -enjoy vitamin C rich fruits and vegetables with meals or when taking iron supplements. Vitamin C rich food ideas include papaya, bell peppers, oranges, and tomatoes 

Inhibitors

• Calcium- avoid consuming dairy products or calcium supplements at the same time as high iron foods or when taking iron supplements

• Tannins- wine, caffeinated beverages

• Zinc- avoid zinc supplements when taking iron supplement or eating a high iron meal 

• EDTA (a food preservative) 

• Phytates and oxalates- in many plant-based foods; this can get tricky since many iron rich plant foods contain these substances, which contribute to non-heme iron’s low bioavailability 

• Insoluble fiber- same as above; avoid taking any fiber supplements with high iron meals or iron supplements 

Should you Supplement?

No, unless your labs indicate depletion and supplements are directed by your physician, do not take supplements to ‘cover your bases’ nor to correct a self-diagnosed deficiency. More is NOT better and supplementing can be very dangerous. Iron is a pro-oxidant (opposite of antioxidant); it promotes the oxidation of cells, increasing free-radicals in your body, thus cell damage- potentially leading to cancer and other disease/ health conditions. Therefore, supplementing with iron should be taken very seriously and only done under direction and monitoring of a physician. 

In addition to the negative effects of iron supplementation in the absence of low iron or anemia, unnecessary supplementation does not improve performance. In other words, if your body has adequate and stable amounts, you will not have any performance benefits from supplementing. The research is inconclusive in regards to the effects of supplementation on performance when body iron stores are declining or in the early stages of depletion. Therefore, it is important for all endurance athletes to have at least biannual blood work to monitor trends in iron transport and storage- this is often done through your physician ordering a CBC and serum ferritin. Detecting declines in iron stores early on allows for appropriate interventions for preventing iron deficiency anemia. 

In the presence of iron deficiency anemia, supplementation is critical and will absolutely improve performance as iron stores and transport become repleted. It is important that a supplementation regimen to correct deficiency or anemia are prescribed and monitored by a physician since unnecessary supplementation can be harmful.