Low iron levels are common among athletes, causing fatigue, lethargy, and reduced performance. Being aware of low iron and running is key to staying active. So what are the signs of low iron in runners? How do we assess iron levels, and what are the best ways to top up iron?
What is iron?
Iron is an essential mineral found in red blood cells and muscle. It carries oxygen to the tissues and plays key roles in the immune system and metabolism. Adequate iron levels maintain energy, so they’re essential for athletic performance.
Ferritin: a measure of your iron stores
Most of the body’s iron sits in red blood cells, as part of the oxygen-carrying molecule haemoglobin. More is found in muscle and other tissues for essential functions such as muscle contraction. The rest is stored as ferritin in the liver and bone marrow, and the body draws on these stores when it needs more iron.
As a guide, a ferritin level above 30 suggests normal iron stores, below 30 indicates low iron stores, and below 12 is very low, signifying empty stores. Note that in athletes, performance can be affected at ferritin levels under about 30–35, even without anaemia (see below).
Low iron and running: why are athletes at risk?
Athletes develop iron deficiency for the same reasons as anyone else. A diet low in iron-rich foods such as meat, chicken, eggs, and green leafy vegetables reduces iron intake, so vegetarian and vegan athletes are particularly at risk. Women are at greater risk, too, losing blood each month through menstruation.
On top of this, training itself raises the risk. Athletes lose more iron through heavy sweating, stress on the gut during intense activity, and red-cell destruction from repetitive impact, such as running. Intense training also demands more iron to transport oxygen to the muscles.
Signs of low iron in runners
The signs depend on severity. In mild deficiency — low iron stores (ferritin) but a normal blood count — the early signs of low iron in runners are persistent tiredness or lethargy despite adequate rest, and reduced stamina, slower recovery, and decreased performance.
When iron drops further, red-cell numbers fall, and oxygen delivery suffers. Later signs include increased breathlessness during workouts, pale skin (face and eyelids), dizziness and headaches after activity, cold hands and feet, muscle and joint pain, dry skin, anxiety or low mood, brittle hair and nails, sleep problems, and worsening performance with early fatigue.
What should you do if you suspect low iron?
See your doctor for assessment. They’ll usually take blood tests for your blood count, iron levels, and other markers, and examine you to rule out other causes of fatigue and reduced performance, which often require their own blood tests.
Common conditions that also affect performance include inadequate calorie intake, overtraining, and medical conditions such as diabetes, low vitamin D, low B12 or folate, thyroid disease, coeliac disease, kidney disease, and heart disease.
It’s also vital to exclude blood loss as a cause. Examples include heavy periods in female athletes, gut blood loss from excessive ibuprofen use, inflammatory bowel disease, or bowel cancer. Ask your doctor whether you need further tests, such as an endoscopy or colonoscopy. Some medications — omeprazole and blood thinners — also reduce iron absorption or increase blood loss.
How do you increase iron in runners?
Not every runner with low iron needs tablets or injections.
Diet
The first step is improving dietary intake. Iron is found in red meat, chicken, fish, eggs, beans, wholemeal products, legumes, dried fruit, and green leafy vegetables. The body absorbs far more from animal sources (15–35%) than from plant sources (2–20%), and absorption improves when vitamin C-rich foods are consumed simultaneously. Conversely, black tea, coffee, phytates (found in whole grains, nuts, and legumes), and calcium supplements reduce absorption.
Aim for iron-rich foods at least five times a week, paired with vitamin C-rich fruit and vegetables. Timing matters too — we absorb more iron in the morning and less after exercise. A sports nutritionist can help optimise your dietary iron.
Iron tablets
Low levels often require more than diet alone. The usual dose is 100–200mg of elemental iron — going above 200mg doesn’t raise iron levels further and brings more side effects (nausea, tummy pain, constipation, diarrhoea).
Recent research has changed how we dose. Alternate-day dosing (one tablet every two days) actually increases overall absorption and reduces side effects, whereas multiple daily doses can reduce absorption. Ferrous gluconate is better tolerated than ferrous fumarate or sulphate. So ferrous gluconate, taken daily or every other day, is a better regimen than taking it several times a day. Take iron tablets on an empty stomach, avoiding coffee, tea, cereals, grains, calcium, antacids, soy, and eggs; a glass of orange juice may help absorption.
Iron tablets can raise iron stores by 30–50% over 6–8 weeks if tolerated. Recheck ferritin and blood count at six weeks. We generally stop tablets once ferritin reaches 60 or above, but sometimes continue for three months — especially in anaemic runners, or where ferritin stays below 30.
Iron injections
When tablets cause side effects or iron needs to be corrected quickly, iron injections are an option — usually given intravenously. IV iron corrects levels rapidly with fewer gut side effects than tablets. Short-lived effects include taste disturbance, headache, dizziness, and sore muscles; serious reactions (allergy or a drop in blood pressure) are rare, so we observe athletes for 30 minutes afterwards. Intramuscular iron into the buttock is also more effective than tablets, but take care to avoid skin staining, and it can cause aching for a few days.
Frequently asked questions about low iron and running
How common is iron deficiency in young female athletes?
Very common. A recent study found that up to 40% of young females aged 12–21 had iron deficiency. Any female athlete with poor performance or fatigue should have a blood count and ferritin checked, because anaemia is a late sign; a normal blood count doesn’t rule out deficiency.
Should runners take iron supplements?
Only if they’re iron-deficient, as determined by blood tests. Studies suggest that supplements improve performance in runners with ferritin levels below 35, with or without anaemia, and also help with fatigue, anxiety, and low mood. The aim is to restore ferritin to 60 or above.
What’s the optimal ferritin level for female runners?
Ferritin below 30 can reduce performance even without anaemia, so in these cases we recommend supplementation to reach 60 or above.
Can I have an iron deficiency without anaemia?
Yes — this is common. A ferritin below 30 indicates iron deficiency, even if your blood count is normal, and it can still affect performance.
Is there a link between vitamin D, iron, and running?
Yes. Adequate vitamin D is associated with less iron loss, so your doctor should check vitamin D as part of investigating low iron. Low vitamin D also affects performance in its own right and should be corrected.
Do ferritin levels change with inflammation?
Yes. Ferritin rises with active inflammation — an infection (such as a chest infection) or inflammatory arthritis. In these situations, a ferritin level below 100 could still indicate low iron stores, making interpretation trickier.
Which medications reduce iron absorption?
Reflux and gastritis medications, such as omeprazole, reduce iron absorption, so try not to take iron tablets at the same time.
What other factors raise the risk of iron deficiency?
Blood donation is a significant but often overlooked factor — studies suggest that up to 50% of adolescent female blood donors show signs of iron deficiency, and 18% have depleted iron stores. Athletes who restrict calories — for weight-class sports or through high energy expenditure — are also at risk.
Final word from Sport Doctor London about low iron and running
Iron is essential for athletic performance. It’s worth checking ferritin in any athlete with reduced performance or persistent fatigue, since deficiency is common and often present without anaemia. Diet is the foundation, with iron tablets or infusions for more significant deficiency.
If you’re a runner experiencing fatigue or declining performance, Dr Masci can assess you in London and arrange the appropriate blood tests. Contact the team here or call +44 (0) 203 488 0350.
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