In January 2019, marathoner Starla Garcia found herself exhausted and struggling to keep up with her normal training partners. She finished the Houston Half Marathon in 1:21:38—speedy for many, but slower and more difficult than she expected.
Garcia’s blood work showed normal hemoglobin levels, the traditional way of measuring iron in the bloodstream. However, her levels of serum ferritin were dropping, a sign she was at risk of becoming iron deficient.
Suddenly, her struggles began to make sense and matched what she knows as a registered dietitian. In a research review published last year in the European Journal of Applied Physiology, scientists estimate up to 35 percent of female athletes experience iron deficiency. In her practice, sports dietitian Rebecca McConville, MS, RD, says it’s more like 75 percent, many of whom experience declines in performance as a result.
The fact that even a dietitian must stay on top of her levels demonstrates just what a nutritional challenge iron often poses. Here’s the full story about why it matters so much—and how to shore up your own supply.
What Is Iron, and Why Should Runners Care?
Your body can’t produce iron on its own, but it needs it to build two key proteins. One, hemoglobin, forms in red blood cells and carries oxygen from your lungs to tissues all over your body. The other, myoglobin, resides in your muscles, storing oxygen to produce the energy that powers your stride.
Not only do these functions matter when you’re in the middle of a repeat or race, they also allow you to reap training’s rewards. The more you run, the more red blood cells and myoglobin you produce, provided you have the raw materials, says Pamela Bruzina, Ph.D., professor of nutritional sciences at the University of Missouri in Columbia, who’s studied iron in athletes.
But if you’re iron-depleted, the process short-circuits, leaving you fatigued and unable to bounce back. Garcia puts it this way: “Think of it in terms of a car—when we’re using more oil in our car, we’re going through it a lot faster,” she says. “We need to make sure we have a consistent flow of healthy blood, the same way a car needs a consistent flow of oil to function and to run.”
When you’re running low on stored iron, you’re iron deficient. Fail to address that deficiency and you’ll stop producing as many red blood cells. Finally, you’ll wind up with low hemoglobin, a condition known as iron deficiency anemia.
How Much Iron Do Runners Need?
Your body absorbs heme iron, found in animals, more easily than non-heme varieties, found in plant foods. If you eat meat, the government recommends consuming 18 milligrams of iron per day between ages 19 and 50. Teen girls need 15 milligrams, older women need 8 milligrams, and pregnant women need 27 milligrams. Vegetarians or vegans who don’t eat meat or seafood should approximately double those amounts.
Athletes may need even more to account for their increased activity. Besides requiring more oxygen-rich blood, training causes inflammation—the same immune-system response your body has to illness or injury. That’s normal, and prompts you to grow stronger and fitter, says McConville, who’s also the author of Finding Your Sweet Spot: How to Avoid RED-S (Relative Energy Deficit in Sport) by Optimizing Your Energy Balance.
But it also boosts levels of a hormone called hepcidin, which further suppress your body’s ability to absorb iron. What’s more, you also lose the mineral through sweat and small amounts of bleeding in your gastrointestinal tract during long races or hard efforts. Each running stride also ruptures red blood cells in vessels on your soles, further depleting you.
What Else Influences Your Levels?
Often, athletes struggle to take in enough iron in the first place, especially if they eat a plant-based, vegetarian, or vegan diet. Low iron levels can be self-perpetuating, McConville says. Iron depletion often alters thyroid function, reducing your appetite. Many iron-rich ingredients are salty and satisfying, which means you might eat less overall and end up steering clear of the foods you most need to replenish.
Intake is only part of the puzzle. Any gastrointestinal or inflammatory condition—think Crohn’s disease or celiac disease—interferes with your body’s ability to shuttle the iron you consume into your bloodstream, Bruzina says.
Estrogen and progesterone also play a role in absorption, so if your hormones are fluctuating for any reason, your iron levels may suffer. On the flip side, if you’re on birth control that stabilizes your levels or have an intrauterine device (IUD) that lightens your period, your risk of deficiency reduces.
Women who have periods, especially heavy ones, lose iron every month through menstrual blood. Pregnant women need more iron because you share stores with your growing baby, Bruzina says. Coming back postpartum, blood loss from giving birth further increases your odds of starting from a deficit, and if you try to lose weight afterward, you exacerbate it.
Iron levels are also impacted by where you are—or specifically, at what altitude. Beginning at around 3,000 feet, thinner air prompts your blood vessels to expand and your body to crank up red blood cell production. That’s exactly why elite athletes head to the mountains to train: Those adaptations super-power their speed and fitness when they head back down to sea level.
But—you guessed it—the process requires additional iron to execute. So whether you’re intentionally altitude training or just heading out for frequent hikes at higher elevations, you’ll want to pay extra attention to your iron levels. Taking a low-dose supplement about 10 days in advance can offer you a buffer and also prevent altitude sickness, McConville says; if you live in the mountains, however, your body will likely adapt.
How Do You Know If You’re Low?
Iron deficiency can set in slowly; by the time you’re officially anemic, you might have had symptoms for up to six to eight weeks, McConville says. But because symptoms are subtle, slow-building, and vague, it can take runners a while to pinpoint the true cause.
You might feel more fatigue than usual throughout the day, even requiring an extra nap. Your motivation to get out of bed or out the door for your run may slip, Garcia says. Once on the road, it may feel harder to hit the same paces and take longer to recover afterward.
The urge to crunch ice—and not just because it’s hot—is a telltale sign of low iron levels, Garcia says. Some people with advanced anemia may even develop pica, a craving for eating things like dirt, flakes of paint, metal, or chalk. You might get more colds, too, because low iron can also suppress your infection-fighting white blood cell count.
There’s also a psychological toll. Iron is a component of mood-influencing neurotransmitters, and deficiency can leach joy and confidence from your running. “You start to wonder, what’s wrong with me? I’ve been working really hard, and I’m just not getting anywhere,” Garcia says. “You might think, ‘I’m just not as motivated as other people,’ or ‘I’m destined to fail.’ Runners can find themselves in these cycles, and it can impact them a lot.”
How—and How Often—Should You Get a Test?
Consulting with a doctor or dietitian who specializes in treating athletes and active populations can guide you to the right test at the right time and put the results in perspective, Garcia says. You might need anywhere from yearly to quarterly checks, depending on your history, symptoms, and risk factors.
Blood panels ordered by primary care physicians typically measure hemoglobin or hematocrit, the proportion of red blood cells in your blood. These results can vary based on how hydrated you are—and as Garcia’s results show, they don’t catch earlier stages of iron deficiency.
Instead, request a serum ferritin test, a measure of iron stored in your tissues. There’s no single, widely accepted cutoff for athletes—another reason to work with a pro on your specific scenario. Many experts place it around 35 micrograms per liter, but others go higher. Garcia, for instance, tends to worry about readings lower than 50, especially heading into a harder block of training.
What are the Best Sources of Iron?
Seafood and meat—especially liver and red meat—offer the most iron. Even if you’re mostly plant-based, incorporating small amounts of animal products could go a long way in boosting your levels, Bruzina says. If you’re a committed vegetarian or vegan, plant-based sources include beans and other legumes, spinach, dark chocolate, molasses, nuts, and fortified breads and cereals.
In addition to what you eat, when and how you consume food with iron matters. Because your inflammation levels are high two to three hours after a hard workout, any iron you eat then might not be absorbed as well.
Calcium and caffeine can also interfere with uptake, so try not to drink milk, coffee or tea, or calcium-fortified orange juice with iron-rich foods. Meanwhile, vitamin C boosts iron absorption, so if you can, combine your beans and spinach with unfortified OJ, citrus fruits, strawberries, or bell peppers. Cooking plant foods in cast-iron skillets also infuses them with an extra dose of the mineral.
Some runners, of course, will need supplements. Based on her test results, Garcia began taking a liquid form of iron every other day. Within a month she began feeling, and running, more like herself.
The following April, she finished the Illinois Half Marathon in 1:19:44—more than two minutes faster. In January 2020, she ran a 2:43:56 at the Houston Marathon, which qualified her for the Olympic Trials Marathon February in Atlanta. Sure, her iron levels were just one small piece of her success, but, Garcia says, they were a crucial one. “Once I bumped it up, it was like night and day,” she says.