A Science-Based Guide to Iron for Runners

It’s a problem all too common for runners – you are training hard, but struggling to hold paces in your runs. You feel exhausted despite sleeping well. You aren’t losing fitness – instead, you may be showing signs of low iron levels. Iron is a crucial mineral for runners, as it plays a role in getting oxygen to your working muscles to produce energy. Without adequate iron levels, you feel fatigued and your runs are slow and sluggish. This article will delve into what you need to know about iron for runners, including signs of low iron, the role of iron, and what to do if you have low iron. 

Disclaimer: I studied nutrition as part of my MSc in Applied Exercise Science. However, this is general advice. For individual situations, please consult your medical professional or a registered dietitian. Do not supplement iron if you do not need it. 

What to know about iron for runners

Iron is a crucial functional component in oxygen transport. Hemoglobin, myoglobin, and cytochromes all include iron – and play a role in oxygen transport and utilization. Thus, iron helps your body bring oxygen to your muscles during exercise. Most running is aerobic, meaning that it uses oxygen plus fat and carbohydrates to produce energy. The more oxygen you can transport and utilize, the more energy you have for running. 

Beyond oxygen transport and utilization, iron is used in other bodily processes. Iron-containing enzymes act protectively against reactive oxygen species, meaning that iron has an antioxidant function. Iron also plays a role in immune function. 

Runners need more dietary iron than sedentary individuals. As a result of endurance training, the body increases hemoglobin (red blood cell) mass and myoglobin content in the muscle. Since your body has more hemoglobin and myoglobin, you need to eat more iron to maintain those. Athletes also lose more iron in their sweat and urine compared to sedentary people. The combination of higher iron needs and higher iron losses makes it much more difficult for athletes, especially female athletes, to maintain adequate iron levels. 

Iron deficiency and running are not a desirable combination. Low iron will make running feel more difficult. More than likely, your performances will suffer and a majority of your runs will feel like a struggle. 

Running with anemia

Anemia is a medical condition in which iron levels are so low that hemoglobin (red blood cell protein) is low. The body’s ability to transport oxygen is impaired, which will obviously have a detrimental effect on running. 

Even before you reach anemia, you can experience low ferritin. Ferritin is the storage form of iron. Ferritin levels will drop before hemoglobin levels, making low ferritin (iron depletion) a precursor to anemia. If iron depletion persists long enough, then serum iron and transferrin levels drop. iron deficiency occurs. If iron deficiency persists untreated, then hemoglobin and hematocrit levels drop, and anemia occurs.

Is running with anemia dangerous? It depends on the severity of your conditions. Some runners with iron depletion or deficiency may be able to keep training, so long as they supplement. More severe anemia may require you to back off of training while you address the issue. If in doubt, speak with your medical professional. 

Symptoms of iron deficiency

Low iron and running create a variety of noticeable symptoms. If you are running with low ferritin or low iron levels, you will often feel like running is a continual struggle. 

Symptoms of low ferritin and low iron levels include:

• Fatigue and sluggishness
• Shortness of breath during runs
• Heavy legs during runs
• Feeling cold all the time
• Feelings of depression or anxiety
• Declined motivation
• Plateaued or declined run performance
• Abnormally higher heart rate on runs

Before you even reach iron depletion, you may experience declined performance. Female athletes may experience fatigue and performance declines with <30 ng/mL of serum ferritin. Male athletes may feel symptoms with <40 ng/mL serum ferritin. These levels are not worrisome in the general population, though. If you have ferritin levels below this level, it is worth speaking to your doctor or sports dietitian about the appropriateness of iron supplementation. 

Causes of anemia

Iron depletion, iron deficiency, and anemia happen when iron intake does not meet requirements. For some athletes, they simply do not consume enough dietary iron for their needs. Plant-based diets may lead to low iron levels if not careful since plant-based sources of iron (non-heme iron) have lower bioavailability of the mineral. 

Other athletes experience higher levels of iron loss in sweat, menstrual blood loss, foot-strike hemolysis, and microscopic GI bleeding. Female athletes are more likely to experience low iron levels due to monthly blood loss. 

For others, iron depletion or deficiency occurs due to absorption issues. Poor absorption can occur from undiagnosed medical conditions, certain medications, other vitamin deficiencies, or even low hepcidin levels. Hepcidin is a hormone that regulates iron status, and it can be impacted by outside factors. A 2020 study in Nutrients demonstrated that fasted training and low carbohydrate availability lead to the upregulation of hepcidin, which leads to lower iron absorption in the gut. 

Since low iron levels are complex, it is always best to attempt to address the root cause. For example, one athlete may have low iron due to inadequate diet, while another may have undiagnosed celiac disease and yet another damaged gut mucosa from excessive NSAID use. If you are diagnosed with low ferritin or iron, it is recommended that you investigate the root cause.

What to know about iron supplements for runners

Iron supplements can be beneficial to runners with low iron levels. While you investigate the root cause of your low iron levels, you might use iron supplements to manage iron depletion, deficiency, or anemia.

Iron supplements come in varying dosage levels. It is recommended that you speak with your doctor about the correct dosage for you. Your doctor may also guide you on whether you should use a pill or liquid form of iron. 

Vitamin C enhances iron absorption via its interaction with hepcidin. Therefore, it can be beneficial to take your iron supplement with vitamin C (orange juice, etc.). Some nutrients, such as calcium, negatively interact with iron absorption. Iron supplements can cause gastrointestinal upset in some runners, so you may want to wait until after your run to take them. Exercise can also impact hepcidin levels. Taking your iron after exercise may be beneficial, as explained in this article on how to improve iron absorption from Asker Jeukendrup.

Never take iron supplements without having bloodwork done first. The symptoms of high iron can mimic the symptoms of low iron. If you supplement iron when your iron levels are already high, you risk worsening the condition and experiencing iron toxicity.  

More tips for managing iron deficiency in runners

Dealing with low iron can feel overwhelming. However, beyond working on a supplementation protocol with your doctor, there are some actions you can take to manage low iron levels.  

Iron level testing tips: 

• If you experience symptoms of iron depletion/deficiency, have your bloodwork done by a doctor. 
• If you already have a baseline of your iron levels, you can visit Quest Diagnostics or use Inside Tracker to retest your levels every 4-6 months. 
• If you are competing at altitude, it is recommended to test your iron levels 3-6 months before your race. 

Dietary tips to improve iron absorption:

• Incorporate iron-rich foods into your diet, including fortified cereals, red meat, poultry, leafy green vegetables, lentils/legumes, and molasses.
• Eat enough carbohydrates and take in supplemental carbohydrates on long runs, in order to regulate hepicidin levels. 
• Work with a registered dietitian to check for any other deficiencies or potential low energy availability.

Importantly, know that iron levels take time to increase. You may not notice an immediate difference when supplementing with iron or increasing your dietary intake. You will need months of deliberate changes to notice a difference – but be patient, because it is worth feeling better once you get your iron levels up.

Want more evidence-based guidance on iron for runners? There is a whole episode of the Tread Lightly Podcast on Iron for Runners! You can find more training tips and advice on new episodes released weekly.

References not already cited:
Jeukendrup and Gleeson. (2016). Sport Nutrition. 3rd edition. Human Kinetics