Why iron matters for energy, concentration, and athletic performance—even when you don’t have anemia.
We all get tired.
Maybe it’s the afternoon slump that has you reaching for another cup of coffee. Maybe you’re a high school athlete struggling to recover between practices. Or perhaps you’re sleeping reasonably well but still waking up feeling like you could use another few hours.
Fatigue is one of those symptoms that’s easy to explain away.
We’re busy. We’re stressed. We’re not sleeping enough. We’re juggling school, work, family, exercise, and everything else life throws our way.
And sometimes, those explanations are exactly right.
But when fatigue becomes persistent, there’s another possibility worth considering: low iron stores.
Iron deficiency is more common than many people realize, particularly among menstruating individuals, endurance athletes, and people who don’t regularly consume iron-rich foods.
And here’s something that surprises many of our clients: You can have low iron stores without having anemia.
Why Iron Matters for More Than Your Blood
Most people associate iron with preventing anemia, but its role in the body extends well beyond healthy red blood cells.
Iron is essential for:
- Oxygen transport: Iron is a key component of hemoglobin, which carries oxygen throughout the body.
- Energy production: Iron helps our cells convert nutrients into usable energy.
- Brain function: Adequate iron supports attention, concentration, and cognitive performance.
- Muscle function: Iron supports oxygen use and energy metabolism during physical activity.
- Exercise recovery and performance: Low iron stores may contribute to fatigue and reduced exercise capacity, particularly in athletes.
When iron stores begin to decline, the body may have less iron available to support these functions, even before anemia develops.
This is especially relevant for active individuals who place additional demands on their bodies through training.
What Is Ferritin, and Why Does It Matter?
When evaluating iron status, one of the most useful laboratory markers is ferritin.
Ferritin is a protein that stores iron, providing an estimate of the body’s iron reserves.
Think of ferritin as your iron savings account.
Your body draws on these reserves when it needs additional iron. If you’re consistently using or losing more iron than you’re replacing, those savings can gradually decline.
Hemoglobin, on the other hand, tells us about the oxygen-carrying protein in red blood cells.
It’s possible to have normal hemoglobin while your ferritin levels are already low.
This is known as iron deficiency without anemia.
Symptoms can include fatigue, reduced exercise tolerance, difficulty concentrating, and sometimes restless legs or hair shedding. However, these symptoms aren’t specific to iron deficiency, so testing is important.
Are We Rethinking What Counts as Low Iron?
Recent clinical guidance has brought renewed attention to how iron deficiency is diagnosed.
The American Society of Hematology’s 2026 guidance identifies a ferritin level below 30 ng/mL as an important threshold for iron deficiency in many adults, rather than relying solely on the historically used cutoff of 15 ng/mL.
For some menstruating individuals experiencing symptoms or additional risk factors, clinicians may consider a threshold closer to 50 ng/mL.
These numbers aren’t universal treatment targets. Age, symptoms, medical history, inflammation, and other laboratory findings all matter.
Ferritin can also rise during inflammation, making iron deficiency harder to recognize from ferritin alone.
That’s why healthcare providers may consider a combination of tests, including a complete blood count, ferritin, and transferrin saturation.
Why Athletes Should Pay Particular Attention to Iron
At McDaniel Nutrition Therapy, we work with athletes of all ages, including middle school, high school, collegiate, and recreational athletes.
Iron deserves special attention in this population.
Athletes may have increased iron needs or experience greater iron losses due to several factors:
Training demands: Exercise increases the body’s need for oxygen delivery and energy production.
Iron losses: Small amounts of iron can be lost through sweat, gastrointestinal bleeding, and exercise-related red blood cell breakdown. These losses can be particularly relevant in endurance sports.
Growth and development: Adolescents need iron to support growth, expanding blood volume, and physical development.
Menstruation: Athletes who menstruate, particularly those with heavy periods, may have additional iron losses.
Inadequate fueling: Athletes who aren’t eating enough overall, restrict certain food groups, or follow poorly planned vegetarian or vegan diets may struggle to meet their iron needs.
Distance runners are a particularly well-studied group, but iron deficiency isn’t limited to endurance sports.
Signs That an Athlete May Need Their Iron Status Evaluated
An athlete with low iron stores might notice:
- Feeling unusually tired during or after practice
- Struggling to maintain a familiar training pace
- Reduced endurance or exercise tolerance
- Difficulty concentrating at school
- Feeling less energetic despite adequate sleep and nutrition
- Unexplained declines in performance
Of course, these symptoms can also result from inadequate calorie intake, poor sleep, illness, excessive training, or other medical conditions.
The goal isn’t to assume every tired athlete needs iron. It’s to recognize when further evaluation may be appropriate.
For parents and coaches, persistent fatigue or an unexplained decline in performance deserves attention rather than simply encouraging an athlete to push harder.
How to Get More Iron Through Food
Food is an important starting point for supporting healthy iron levels.
There are two main types of dietary iron.
Heme iron comes from animal foods and is generally more readily absorbed.
Sources include:
- Beef and other meats
- Poultry, particularly dark meat
- Fish
- Shellfish, including oysters and clams
Non-heme iron is found in plant foods and fortified products.
Sources include:
- Lentils and beans
- Tofu and tempeh
- Pumpkin seeds
- Spinach and other leafy greens
- Iron-fortified cereals
- Whole grains
Both forms can contribute meaningfully to your daily iron intake.
A Simple Trick to Improve Iron Absorption
Pair plant-based iron sources with vitamin C-rich foods.
For example:
- Lentils with tomatoes and bell peppers
- Black beans with salsa
- Tofu with broccoli
- Iron-fortified cereal with strawberries
- Hummus with red peppers
Vitamin C helps the body absorb non-heme iron more efficiently.
Coffee and tea consumed with iron-rich meals can reduce non-heme iron absorption. Calcium supplements may also interfere with absorption when taken at the same time as iron supplements.
You don’t need to eliminate these foods or beverages. Timing can sometimes make a difference.
When Food Alone Isn’t Enough
As registered dietitians, we strongly believe in the value of food-first nutrition strategies.
But we also believe in being realistic.
When iron stores are already depleted, food alone may not restore them quickly or effectively, particularly if someone continues to lose iron through menstruation, has absorption difficulties, or has substantially increased needs.
In these situations, an iron supplement may be recommended.
Ferrous sulfate is one of the most widely studied and commonly used forms of supplemental iron. It’s effective and relatively inexpensive, but it can cause digestive side effects such as nausea, constipation, and abdominal discomfort.
Other forms, including iron bisglycinate, may be better tolerated by some individuals.
Research also suggests that alternate-day dosing can improve iron absorption efficiency for some people, although the ideal schedule depends on the individual and the amount of iron prescribed.
For athletes, timing may matter as well.
Strenuous exercise temporarily increases hepcidin, a hormone that regulates iron absorption. This can make iron absorption less efficient during certain periods following exercise.
A sports dietitian can help athletes coordinate their nutrition, supplementation, and training schedules when appropriate.
One important caution: More iron is not always better.
Iron supplements should not be started simply because someone feels tired. Excess iron can be harmful, and unnecessary supplementation may delay the diagnosis of another cause of fatigue.
Testing and individualized recommendations are essential, especially for children and adolescents.
What If Iron Supplements Don’t Work?
Sometimes, despite dietary improvements and oral supplementation, iron stores remain low.
This may happen because of ongoing blood loss, poor absorption, difficulty tolerating supplements, or an underlying medical condition.
In certain situations, healthcare providers may recommend intravenous (IV) iron.
IV iron delivers iron directly into the bloodstream, bypassing the digestive tract.
Kristen Sanfilippo, MD, MPHS, a hematologist at WashU Medicine, emphasizes that oral iron remains an effective, less expensive first-line treatment for most people.
However, when oral iron isn’t tolerated or iron stores fail to improve despite appropriate treatment, IV iron may be worth discussing.
Infusions can replenish iron stores more quickly, but they also involve additional costs, monitoring, and potential side effects.
They aren’t necessary or appropriate for everyone.
Just as importantly, restoring iron stores doesn’t automatically address why they became depleted in the first place.
Identifying and treating the underlying cause remains an essential part of care.
When Should You Ask About Iron Testing?
Consider discussing iron testing with your healthcare provider if you or your child are experiencing persistent fatigue, particularly when accompanied by additional risk factors such as:
- Heavy menstrual periods
- Endurance training or high-volume athletic participation
- Vegetarian or vegan eating patterns
- Limited food intake or restrictive eating
- A history of iron deficiency
- Gastrointestinal conditions that affect nutrient absorption
- Unexplained changes in exercise performance
A complete evaluation may involve more than iron testing. Sleep, overall energy intake, thyroid function, medications, and other health factors may also need consideration.
The Bottom Line: Don’t Ignore Persistent Fatigue
Being tired occasionally is part of being human.
But feeling consistently exhausted, struggling through workouts that once felt manageable, or having difficulty concentrating throughout the day shouldn’t automatically be dismissed as normal.
For some people, improving sleep or eating enough throughout the day may be the missing piece.
For others, low iron stores could be contributing.
And sometimes, several factors are working together.
At McDaniel Nutrition Therapy, we help clients look at the bigger picture: nutrition, activity, recovery, lifestyle, and the medical factors that influence how they feel.
Whether you’re a parent concerned about your young athlete, an adult trying to maintain your energy, or someone navigating changing nutritional needs, understanding your iron status can be one useful piece of the puzzle.
Just because you can push through fatigue doesn’t mean you should have to.
Concerned that your nutrition may be affecting your energy or athletic performance? Our registered dietitians can help you evaluate your dietary intake, identify potential gaps, and develop a personalized nutrition plan in collaboration with your healthcare team.