Low Iron Sucked So Much Joy Out of My Running, but 3 Experts Gave Me a Roadmap to Fix It.

I still remember the first time I learned about foot strike hemolysis. I thought my doctor was making a joke. She said a possible explanation for my low iron levels was the breakdown of red blood cells from my feet hitting the pavement every time I went for a run. And those red blood cells contain most of the body’s iron supply.

“So you’re telling me that I’m essentially squashing my blood cells with my feet?” That sounded like it could be a punchline in an episode of Scrubs.

She paused. “Well, sort of, yes. But it’s a lot more complex than that.”

At that time, I had no idea how much more complex. Iron absorption is, at least in my mind, one of the body’s most confusing and frustrating mechanisms. And while foot strike hemolysis remains one of the many factors that can contribute to iron deficiency in runners, it may not play as significant a role as my doctor believed more than a decade ago.

Fortunately, we now understand a lot more about iron and why runners—especially females—are more at risk for deficiency than the general population. In a study published in Blood, the journal of the American Society of Hematology, researchers collected blood samples from 277 marathon and half marathon runners at the 2021 Detroit Free Press Marathon’s prerace expo. A total of 107 male runners and 170 female runners were tested. Fifteen percent of the male runners and 47.6 percent of the female runners met the study’s criteria for clinical iron deficiency.

In a study published in JAMA Open Network in 2024 examining the general population of 8,000 men and women, about 14 percent met the criteria for absolute iron deficiency (severe reduction or absence of iron stores) and about 15 percent had functional iron deficiency (presence of iron stores but insufficient availability).

I talked to experts who investigate iron from every angle—from emerging research on its metabolism, to diagnosing symptoms of deficiency, to providing treatment and monitoring. Here’s what all runners need to know about this mineral, including risk factors for deficiency, and what you can do to bring your levels up to optimal status.

Peter Peeling, PhD, is a leading researcher at the University of Western Australia and the Western Australia Institute of Sport, whose work focuses on iron metabolism in athletes. He views athletes at high risk for iron deficiency in four groups:

1. Menstruating females
2. Endurance athletes
3. Athletes in weight-restricted or aesthetic sports
4. Vegetarian or vegan athletes

Female athletes may be one of the more apparent groups, because they lose blood each month through the menstrual cycle. Those with heavy menstrual bleeds are even more at risk.

“But even if your period is light or regular, you’re still losing blood every month, and that is an ongoing source of iron loss,” says Ariela Marshall, MD, a Minnesota-based consultative hematologist with expertise in women’s hematology. “One third or more female runners experience iron deficiency,” she adds. (Marshall’s estimate aligns with Cleveland Clinic’s cited stats among female athletes.)

Vegetarian and vegan athletes are also at increased risk of low iron because the body better absorbs heme iron, which comes from animal products, compared with nonheme iron, which comes from plants.

The reasons for iron deficiency among other athlete subgroups may appear less obvious.

“Endurance athletes are at risk because of a combination of small things that add up—namely sweating, gastrointestinal bleeding, and inadequate nutrition,” Peeling says.

On a runner’s average day, this could look like losing trace amounts of iron through sweat during a workout. During that run, the body diverts blood away from the digestive tract to support the working muscle groups, which not only can result in an unexpected midrun bathroom break, but can also stress the intestinal lining and lead to microscopic GI blood loss through the stool. Post-workout, that runner might not refuel with enough calories and iron-rich foods to meet the high demands of the training session.

All these factors can act like a slow leak that gradually depletes iron stores over time, according to Peeling, because they’re happening every day, day after day, and sometimes multiple times per day.

Peeling adds that the body can recover and reuse some of the iron lost through foot strike hemolysis, because the iron from ruptured red blood cells still remains inside the bloodstream. This is unlike the cases of sweating, menstrual losses, and GI bleeding, where iron is leaving the body. In comparison, foot strike hemolysis’s contribution to iron loss may only be minor.

Individuals competing in weight-restricted or aesthetic sports are another group at higher risk for iron deficiency. These athletes can face pressure to drop weight or achieve a specific physique for competition, which can lead to under-fueling and a resulting energy deficit.

On its own, an energy deficit can contribute to low iron because low-calorie intake is associated with a lower intake of iron, says Kelly Jones, RD, CSSD, a board-certified sports dietitian who works with endurance athletes. But that’s not the only way insufficient fueling can affect iron stores.

“Diets with low-energy availability or low-carbohydrate availability may raise hepcidin levels [a hormone that regulates iron absorption in the body], which makes it more challenging to absorb any iron that is consumed,” says Jones.

We need hepcidin because it helps prevent our bodies from absorbing too much iron, which is toxic. But it becomes problematic when you consider endurance exercise also raises hepcidin and then keeps it elevated for a few hours. “Athletes training regularly or multiple times a day have less of a window to absorb the iron they need,” Peeling says.

Runners already require more iron in their diets than the average individual, because we lose more iron on a daily basis, and we also use more iron on a daily basis to make red blood cells, produce cellular energy, and transport oxygen. “Just like runners need more calories, there’s an increased metabolic need for all types of nutrients, iron among them,” Marshall says.

Runners also need to have higher ferritin levels—the body’s stored form of iron—at baseline than the general population to perform and feel their best.

“The normal range for ferritin starts at 10 to 15 ng/mL in many labs, but we’re trying to get that increased to about 30, and up to 50 for menstruating women,” Marshall says.

At this time, the American Society of Hematology is considering higher ferritin thresholds as part of its ongoing guideline-development process for the diagnosis of iron deficiency. (Some good news: I can confirm that my lab recently adjusted its ferritin threshold from 11 to 30 ng/mL!)

For all athletes—not just menstruating females—a ferritin level below 50 ng/mL may be a threshold where the body begins to signal that more iron absorption is needed. “We know ferritin below 50 ng/mL starts to impact how hepcidin behaves,” Peeling says. A 2023 narrative review by Peeling and his colleagues found that ferritin levels of 30 to 50 ng/mL were “suboptimal” because athletes in that range may exhibit a hepcidin response pattern that is not ideal for training adaptation.

Runners—like me—who experience restless legs at night have even higher ferritin targets. Neurologists and sleep specialists who collaborate with the Restless Legs Syndrome Foundation recommend ferritin levels above 75 to 100 ng/mL. Some individuals even require ferritin levels above 100 ng/mL to improve their symptoms.

Why so high? Restless legs syndrome (RLS) is linked to insufficient iron availability in certain parts of the brain, according to a 2022 review published in Experimental Neurology. Researchers believe some individuals may need higher ferritin levels to increase the likelihood that adequate iron reaches those regions and supports normal neurological function.

For years, I thought having twitchy legs that disrupted my sleep at night was something that just came with marathon training. Turns out, it was iron.

The first signs of iron deficiency runners typically notice are fatigue that persists despite good recovery practices, such as getting enough sleep and taking a rest day, or that their typical training pace feels consistently more taxing.

Other symptoms can include: dizziness, headaches, shortness of breath, heart palpitations, hair loss, brain fog, trouble concentrating, irritability, brittle nails, easy bruising, restless legs, and cravings for dirt, chalk, or ice. (I specifically remember fighting the urge to go after the potting soil in my mom’s garden shed with a spoon—yikes.)

But bloodwork offers the only true way to know if you are iron deficient.

“If you remain iron deficient for too long, there’s a risk of developing anemia, which means that your actual red blood cell count is low. But you can have symptoms long before anemia develops,” Marshall says.

Marshall explains that some healthcare providers may say they’re not concerned about a runner’s complaints of fatigue when hemoglobin looks normal. But she says this is when runners need to advocate for themselves and request a full iron panel that includes key markers, such as ferritin. This can confirm if low ferritin is the cause of fatigue, even though other key blood markers look normal.

An important note: Schedule your bloodwork for a time when you are rested and healthy, because inflammation and illness can falsely elevate ferritin levels.

According to Jones, runners looking to raise their ferritin—and keep it up—should focus on always eating enough to meet their energy needs and increasing the amount of iron in their diets.

Some iron-rich foods Jones recommends include meats, poultry, shellfish (particularly clams and oysters), pulses (such as lentils and beans), soy foods, whole grains, leafy greens, pumpkin seeds, hemp seeds, cashews, tahini, and dark chocolate.

To boost absorption, pair these foods with vitamin C. “This, of course, includes citrus fruits and what I find to be a favorite addition to runner recovery meals: 100 percent orange juice,” Jones says. Other vitamin C heavyweights include kiwi, strawberries, guava, cantaloupe, bell peppers, broccoli, Brussels sprouts, and potatoes.

Jones adds that one lesser-known enhancer of iron absorption is beta-carotene, which you can get from orange, red, and green produce such as sweet potatoes, carrots, squash, mango, red peppers, broccoli, and kale.

Additionally, eating consistently and regularly is instrumental in maintaining healthy iron stores among Jones’s athletes. She says runners should not skip breakfast or go hours without a meal or snack, and they also need to properly fuel their workouts. That means taking in gels during a long run—even when we don’t feel like it—and eating a post-workout snack, even if you don’t feel hungry. “Consistency in meal timing and composition helps provide proper nutrition for energy and recovery,” Jones says. In short, well-fueled and recovered runners can better absorb and utilize the iron they consume.

While it’s possible for some runners to get enough iron through their diet alone, Jones says it’s most efficient to add an iron supplement while working on those iron-forward dietary changes. Marshall agrees: “I will say it’s almost impossible to get enough iron from the diet once there is a significant deficiency—it’s going to have to come with a supplement.”

Hepcidin—that hormone that regulates iron absorption—gradually rises throughout the day, so Jones recommends taking an iron supplement in the morning, when hepcidin is at its very lowest. You’ll also want to put at least one hour between your supplement and your morning coffee or tea. These beverages contain naturally occurring compounds called polyphenols, which can significantly impair iron absorption. Foods high in calcium can also decrease your supplement’s effectiveness.

Jones understands caffeine is simply non-negotiable for many early morning runners, and you don’t have to forgo your prerun cup of coffee. “If you’re getting up to train early, you can take your iron right after your workout, because the post-exercise increase in hepcidin does not peak until about three hours post-workout,” she says. But don’t wait too long—Marshall suggests downing that pill within 30 minutes of finishing your run to ensure you beat the upcoming hepcidin spike.

The good news is that you don’t necessarily need to supplement every day. When you consume an iron supplement, the body responds by producing hepcidin. Spacing doses by 48 hours gives hepcidin more time to fall back to baseline before your next pill. For this reason, at least one study suggests supplementing with iron every other day—rather than every single day—can actually be more effective. Whether that directly translates into faster increases in ferritin, however, remains less clear.

Finally, iron comes in many forms, and the type you take matters. Jones recommends ferrous bisglycinate because research shows it’s very well absorbed and significantly more gentle on the gut. (Personally, I can say that ferrous bisglycinate is the only form of iron I’ve tried that I can tolerate without any constipation or nausea—and I have tried many.)

According to Peeling, some people are genetically predisposed to poor iron absorption. “Variants in the TMPRSS6 gene have been shown to impact hepcidin regulation and iron absorption, so some people may be battling their genetics—that’s a tough one to overcome,” he says.

Additionally, gastrointestinal disorders such as celiac disease and Crohn’s disease sometimes go undiagnosed, which can cause an ongoing drain on iron stores. Runners who experience frequent exercise-related GI distress can also have sneaky iron losses.

That said, in any situation where ferritin levels don’t respond to supplements, or your stomach can’t consistently tolerate them, Marshall encourages pursuing an iron infusion with your doctor’s help.

“If the oral iron isn’t cutting it, we don’t want to let people suffer symptoms while we figure out what’s going on. Giving IV iron and investigating the cause of ongoing iron losses can be done at the same time,” Marshall explains. “I think general practitioners need to be quicker about prescribing IV iron, or [they should] refer those patients to a hematologist to start talking about IV iron treatments.”

I spent most of my adult life struggling with supplements and delaying iron infusions. This past year, I finally started getting the IV iron I needed. As a result, I’m sleeping better, my easy runs no longer feel like death marches, and I’m not desperately craving naps (or dirt) in the middle of the day. And, in turn, all these things have significantly helped improve my mood and lower my anxiety.

Overall, getting my iron levels back to optimal has been an absolute game changer—not just for my running, but for my overall quality of life.

Morgan Petruny

Morgan is a gear editor who has been with Runner’s World since 2017. She started as an intern ghostwriting The Warmup, a bygone version of the daily RW newsletter. Now, she tests and reviews anything you might find on runners’ feet-from crew socks and compression boots to carbon-plated super shoes.

A lifelong runner and shoe geek, Morgan has been chasing the perfect pair of kicks since she joined her grade school cross-country team. Since then, she ran as a Division I walk-on for the cross-country and track & field teams at the University of Delaware, where she studied English and Biology. She has one full marathon under her belt, and has raced more halfs and 5Ks than she can count.