Running can feel exhausting, but it shouldn’t leave you so gassed you can’t get off the couch for the rest of the day or that it takes you a full week to recover from a workout. Too often, that sense of fatigue is accepted as a part of training—when it should be looked at as a red flag.
Fortunately, the rise of at-home blood tests is waking athletes up to deficiencies that could be affecting their workouts. And “ferritin” is one of the most common ones to pop up for female runners. Even pro Keira D’Amato has posted about addressing low ferritin levels—before she went on a spree that most recently resulted in breaking the American women’s marathon record and finishing eighth in the World Athletics Championships marathon in Eugene, Oregon, in mid-July.
So why do low ferritin levels wreak havoc on your performance? Here’s what you need to know.
What Is Ferritin?
Ferritin is a protein in which your body stores extra iron, says Meghann Featherstun, R.D.. Iron is a mineral your body uses to make hemoglobin, a protein in red blood cells that carries oxygen from the lungs to all parts of the body, and myoglobin, a protein that provides oxygen to muscles. That makes it a crucial one for runners, as it “plays a role in oxygen transport to muscles (so we can maintain pace and performance), energy production, immunity, and even cognition,” says Sarah Schlichter, a registered dietitian nutritionist and host of the Nail Your Nutrition podcast.
Standard blood tests will measure your iron serum levels, aka, what’s currently circulating in your blood.
“Our bodies work really hard to keep serum levels where they need to be to be healthy, but that doesn’t show well how well you’re absorbing and storing nutrients,” Featherstun says. “Whereas, if you look at ferritin—in conjunction with iron percent saturation and total iron binding capacity—you’re going to see the bigger picture related to a runner’s performance.”
For people assigned female at birth, normal ferritin levels are between 14.7 and 205.1 nanograms per milliliter (ng/mL), according to the Cleveland Clinic. That’s a massive range. For female athletes, levels of at least 25 ng/ml can be advantageous for performance, time to exhaustion, and VO2 Max, according to older research published in the journal Medicine & Science in Sports & Exercise. But “more recent research shows that your ferritin levels should be at least 40 ng/ml,” says Featherstun.
What Does It Mean If Your Ferritin Levels Are Low?
You may not feel iron losses in the moment, but as those accumulate (and aren’t addressed), you’ll definitely feel the effects. “Runners lose iron through sweat, gastrointestinal losses, the menstrual cycle, urine, and a process called foot strike hemolysis, where red blood cells are broken down through the impact of our feet hitting the ground,” Schlichter says.
If a ferritin test reveals that your blood ferritin level is lower than that 40 ng/ml threshold, it indicates your body’s iron stores are low and you have iron deficiency. That means your iron intake is inadequate to offset iron losses, your body isn’t absorbing iron properly, or you’re losing excess iron somehow, Schlichter says.
And without enough stored iron, your body’s capacity to deliver oxygen to your muscles will be reduced, which will affect your performance.
“If we don’t have enough iron in our body, we can’t create the energy we need to fuel our paces, you won’t be able to recover from workouts as quickly, and you might have difficulties with fatigue, lethargy, concentration, and mood,” Featherstun says.
It’s not an uncommon issue: The prevalence of iron deficiency is around 15 to 35 percent in female athletes and 3 to 11 percent in males, according to a 2019 paper published in the European Journal of Applied Physiology. “Women of reproductive age are typically at a higher risk of iron deficiency due to menstruation blood loss,” Schlichter says. But diet—and consuming less calories overall—also play a role.
If that iron deficiency goes unchecked, it can devolve into anemia, a condition in which the blood doesn’t have enough healthy red blood cells to carry oxygen to your body’s tissues. Your symptoms will worsen as your deficiency worsens, especially if your iron stores bottom out. “If someone’s ferritin is in the teens or single digits, it’s in the toilet,” Featherstun says.
How to Fix Low Ferritin Levels
The best way to up your ferritin levels is to eat iron-rich foods like red meat and dark meat regularly.
“Iron is really hard for our body to absorb, and heme iron, which is found in animals, is the most easily absorbed type,” Featherstun says. Poultry, shrimp, and shellfish are good options, too. But there are also plant sources of iron, like leafy greens, pumpkin seeds, apricots, dark chocolate, and fortified cereals and breads, she adds. “We just have to eat a ton of these to absorb enough.” Pairing these foods with a food source of vitamin C, such as orange juice, strawberries, peppers, or potatoes can help increase absorption, as can cooking in a cast-iron skillet, Schlichter says.
If your iron levels are too low, you can take a supplement. They’re not an immediate fix, but “you should feel an abatement of symptoms within three to four weeks,” Featherstun says. “It can take two to four months—or even longer—to get level.”
When it comes to supplementation, remember how hard it is for your body to absorb iron and take it separately from supplements like magnesium and calcium, which will compete for absorption, she says.
Before supplementing, consider your regular diet, your menstrual cycle and your symptoms. And “have your full iron panels looked at by a doctor or medical provider,” says Schlichter—don’t just draw your own conclusions if you do an at-home blood test. (P.S. Ferritin can increase in the recovery period after acute endurance exercise, Schlichter adds, so don’t get tested right after an intense or long run.)
Runners with any recent history of iron depletion/deficiency, who follow a vegetarian or vegan diet, or show signs of low energy availability, should be tested quarterly, a 2019 article published in a European Journal of Applied Physiology recommended. Otherwise, female athletes should be checked biannually.
An iron deficiency doesn’t have to derail your training—but it does require paying attention to your body and your diet and being vigilant about getting your blood checked twice a year.