No Energy to Run- Even for Your Easy Runs
Are you feeling tired all of the time, before your runs and completely exhausted even after an easy run? Are you sleeping more than usual? Low iron could be the problem.
After experiencing this myself during marathon training last year and hearing similar stories from fellow runners, I decided to explore the connection between low iron and running.
What do we need iron for?
Iron helps your red blood cells carry oxygen. Your muscles rely on that oxygen to function properly. Without enough iron, your body can’t deliver the oxygen your muscles need, which means your performance, recovery, and energy levels all take a hit.
Iron is lost from the body in several ways, one of the most common being through sweat. This makes runners more susceptible to low iron when training in hot conditions. That’s what happened in my case. After moving to a warmer climate, most of my runs were in higher heat. Suddenly, my body needed more sleep, I was struggling to complete my easy runs and I just felt exhausted. I reduced my training load to give my body more recovery time but I still felt exhausted. A blood test confirmed that my iron was very low.
Symptoms of Low Iron in Runners
I had experienced the classical signs of low iron. Low iron running symptoms can look like overtraining or burnout. Running seems to require more effort than usual. It is more than just having a bad day.
Symptoms may include:
- Legs feel heavy
- More out of breath than usual
- Pace slowed down
- Persistent fatigue
- Frequent illness
- Cold hands and feet
- Restless legs
- Dizziness
- Reduced appetite
- Brain Fog
What Causes Low Iron in Runners?
Iron loss in runners doesn’t happen all at once. It’s the result of several ongoing processes—some obvious, others more subtle. Over time, especially during high training loads or hot weather, these losses add up and can lead to low ferritin (the protein that stores iron in our body), or full-blown iron deficiency.
1. Sweat Loss
Iron is lost in sweat, and this becomes more significant in warm or humid conditions. The hotter you train, the more you sweat, and the more iron you lose. This affects endurance athletes in particular, who spend long periods training outdoors.
2. Gastrointestinal Microbleeds
Running, especially at longer distances, can cause minor gastrointestinal bleeding. Repetitive impact, reduced blood flow to the gut during exercise, and mechanical jostling of the intestines all contribute to this.
A study in the International Journal of Sports Medicine (1988) found that runners, particularly marathoners, had a higher incidence of blood loss in stool samples post-exercise, even if they weren’t aware of any symptoms (Walker et al., 1988).
3. Footstrike Hemolysis
Every time your foot hits the ground, there’s a shockwave through your body. In distance runners, this repeated impact destroys red blood cells in the small vessels of the feet, a process known as footstrike hemolysis.
This form of red blood cell breakdown lowers haemoglobin and reduces iron availability. Fallon (2004) notes in the British Journal of Sports Medicine that even mild footstrike hemolysis, when paired with sweat and other losses, can meaningfully reduce iron levels over time.
4. Menstruation (in Female Runners)
Menstrual blood loss is a major contributor to iron deficiency in female athletes. Women of reproductive age already have higher iron requirements, and combining this with endurance training can push iron levels into a deficient range quickly.
The Journal of the International Society of Sports Nutrition (McClung et al., 2009) notes that up to 50% of female endurance athletes may be iron deficient, many of them unaware.
5. Inadequate Dietary Intake
Many runners eat healthfully but may not get enough iron, especially if they avoid red meat, follow plant-based diets, or simply don’t eat enough overall to meet high training demands. Non-heme iron from plants is less bioavailable, and without enough vitamin C or proper food pairings, much of it goes unabsorbed.
6. Increased Hepcidin Post-Exercise
After a hard session, your body temporarily raises hepcidin levels. Hepcidin blocks iron absorption from the gut for several hours post-exercise. If you routinely train hard and don’t time iron intake carefully, you may struggle to absorb enough iron from food or supplements.
A study published in the European Journal of Applied Physiology found that endurance athletes, especially females, showed elevated hepcidin (a hormone that regulates iron) levels after training. This blocked iron absorption and increased the risk of iron depletion (Peeling et al., 2007).
How Runners Can Increase Their Iron Intake
You can improve your iron intake through food. Good sources include red meat, liver, chicken, sardines, lentils, tofu, spinach, pumpkin seeds, and fortified cereals. Heme iron from animal products is easier for your body to absorb than non-heme iron from plant foods.
To improve absorption, eat iron-rich foods with vitamin C sources like oranges, strawberries, bell peppers, or tomatoes. Avoid taking iron alongside calcium-rich foods or drinks like milk, yogurt, or cheese.
Cooking with cast iron pans can also increase the iron content of your meals. A study in the Journal of Food Composition and Analysis found that foods cooked in cast iron, especially acidic ones like tomato sauce, absorbed measurable amounts of iron from the cookware (Geerligs, 2007). This might be a small boost, but for runners with marginal levels, it can help.
Iron Supplements for Runners: What to know
When diet alone isn’t enough, supplements can help restore your iron. Ferrous sulfate is a common form. It’s effective but can irritate your stomach. Alternatives like ferrous bisglycinate or ferrous fumarate may be easier to tolerate.
You should never start iron supplements without checking your levels first. Your doctor will measure your ferritin and haemoglobin to decide what dose is appropriate. Many athletes with low ferritin (below 30 ng/mL) are advised to take 100–200 mg of elemental iron per day for several months. You’ll need to retest regularly.
Taking iron with vitamin C and on an empty stomach improves absorption, but some people experience nausea. If that’s the case, try taking it with a small amount of food, not dairy, and separate it from coffee or tea, which can also block absorption.
In one review focused on athletes, researchers noted that iron supplementation improved performance and reduced fatigue, particularly in female endurance athletes (McClung & Gaffney-Stomberg, 2011).
Why Female Runners are More Prone to Low Iron Levels
Female runners are especially vulnerable to low iron due to a combination of factors. Menstruation causes monthly blood loss, which increases iron requirements. Endurance training adds further stress through sweat loss, footstrike hemolysis, and higher overall demand. Without enough dietary iron or proper timing of supplements, levels can drop quickly. Low ferritin is common in female athletes and often goes unnoticed until fatigue, poor performance, or frequent illness sets in. Regular blood tests and a focus on iron-rich foods are essential to maintain energy, support recovery, and avoid long-term health issues.
Hemochromatosis and Running
Some people, especially of Northern European descent, have a genetic condition called hereditary hemochromatosis. It causes the body to absorb and store too much iron. This is sometimes called the Celtic Curse because it’s common in Ireland and parts of the UK.
Hemochromatosis can cause fatigue, joint pain, liver problems, and even heart disease if left untreated. Bronze-colored skin is another sign. The condition is often diagnosed later in life, but symptoms can appear much earlier.
Taking extra iron without knowing your actual levels can be harmful. Fatigue is a symptom of low and high iron. Some people assume they’re deficient and start supplementing on their own, only to end up with iron overload, which can damage the liver, heart, and other organs. Always test first, then treat.
Running Exhausted
Iron levels can make or break your training. You can eat well, train smart, and still hit a wall if your body doesn’t have enough of this vital mineral. Low ferritin levels in runners are easy to miss but have a real impact on how you feel and perform.
If you are feeling exhausted all the time, it may be a case of overtraining or it may be a lack of iron. Running in the heat will increase this risk. During the summer, be extra vigilant. Keep your diet topped up with iron rich food. Track your symptoms. Get your blood checked. Only supplement when needed. Don’t let iron deficiency derail your training. Prevention is always better than cure.
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