Iron for Athletes: When Your Performance Needs a Boost

Is that midday fatigue during training actually iron deficiency in disguise? After 18 years in my Boston practice—and seeing hundreds of endurance athletes—I’ve learned that iron supplementation isn’t a one-size-fits-all solution. The biochemistry here is fascinating, but let’s cut through the noise.

What the Research Actually Shows

Mechanistically speaking, iron’s role in hemoglobin synthesis means it’s literally carrying oxygen to your muscles. But here’s where things get tricky: athletes have higher iron needs due to hemolysis (red blood cell breakdown from foot strike), sweat losses, and increased red blood cell production. A 2023 meta-analysis in the British Journal of Sports Medicine (doi: 10.1136/bjsports-2022-106678) pooled data from 14 studies with 1,847 athletes and found that iron-deficient non-anemic athletes who supplemented improved their VO₂ max by 5.2% on average compared to placebo. That’s not trivial—it could shave minutes off a marathon time.

But—and this is important—the same analysis showed no performance benefit for athletes with normal iron status. This drives me crazy: supplement companies pushing iron to every athlete when the evidence clearly says otherwise.

Dr. Peter Peeling’s team in Australia published a 2022 randomized controlled trial (PMID: 35427461) following 86 female endurance athletes for 12 weeks. They found that those with ferritin levels below 30 μg/L who took 100 mg ferrous sulfate daily improved their 3,000m run times by 3.7% (p=0.02), while those with normal ferritin saw zero improvement. The numbers matter: n=86, 12-week intervention, specific threshold.

I’ll admit—ten years ago I was more liberal with iron recommendations. But the data since then has refined my approach. NIH’s Office of Dietary Supplements updated their fact sheet in 2024 noting that athletes, particularly females, may require 1.3-1.7 times the RDA of 18 mg. But that doesn’t mean megadosing.

Dosing & Specific Recommendations

First, get tested. I can’t emphasize this enough. Ferritin (storage iron) below 30 μg/L in athletes often warrants intervention, even if hemoglobin is normal—that’s “sports anemia.” Hemoglobin below 12 g/dL in women or 13 g/dL in men means true iron-deficiency anemia.

For correction: 30-60 mg elemental iron daily. Not milligrams of ferrous sulfate—that’s different. Ferrous sulfate contains about 20% elemental iron, so 325 mg ferrous sulfate = 65 mg elemental iron. The biochemistry nerds will appreciate that ferrous bisglycinate has better absorption and fewer GI side effects because it uses amino acid transporters instead of competing with other minerals.

Timing matters: Take on an empty stomach with 100-200 mg vitamin C (ascorbic acid). Vitamin C reduces ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), which is better absorbed. Avoid calcium-rich foods, coffee, or tea for 2 hours—they inhibit absorption. I actually take my own iron supplement this way when I’m training heavily.

Brands I trust: Thorne Research’s Iron Bisglycinate (25 mg elemental iron per capsule) or Pure Encapsulations’ OptiFerin-C (which includes vitamin C). I’d skip the generic drugstore brands—ConsumerLab’s 2024 analysis of 42 iron products found that 23% failed quality testing for disintegration or contained different amounts than labeled.

Who Should Avoid Iron Supplements

This is critical: individuals with hemochromatosis (iron overload disorder)—obviously. But also anyone with normal iron status. A 2021 Cochrane review (doi: 10.1002/14651858.CD013867.pub2) of 18 RCTs with 4,521 participants found that unnecessary iron supplementation in replete individuals increased oxidative stress markers by 22% (95% CI: 15-29%).

Patients with chronic inflammation (like rheumatoid arthritis) often have elevated ferritin that doesn’t reflect true iron stores—supplementing can worsen inflammation. And honestly, if you’re a male athlete eating red meat regularly with normal labs? You probably don’t need it.

I had a patient last year—a 28-year-old male triathlete—who came in taking 100 mg daily “for energy.” His ferritin was 150 μg/L (perfect). We stopped it, and his GI issues cleared up within a week. Point being: test first.

FAQs

Can’t I just eat more red meat instead?
Sure—3 oz of beef has about 2.1 mg heme iron (better absorbed). But a female endurance athlete needing 25 mg daily would need to eat 12 servings. That’s… a lot. Plus, heme iron from meat increases colorectal cancer risk in high amounts.

How long until I see performance improvements?
Ferritin rises first—usually within 3-4 weeks. Hemoglobin takes 6-8 weeks. Performance metrics (VO₂ max, time trial) often improve around 8-12 weeks. The 2022 trial I mentioned showed significant changes at 12 weeks.

What about “iron infusion” trends?
IV iron bypasses gut absorption issues and works faster. But it’s expensive, has risks (anaphylaxis in 1:200), and should only be for severe deficiency (ferritin <15 μg/L) with oral intolerance. Not a performance “boost.”

Do plant-based athletes always need supplements?
Not always—but non-heme iron from plants is absorbed at 2-20% vs. 15-35% for heme iron. Pairing with vitamin C helps. Still, most vegan athletes I see need supplementation, especially females.

Bottom Line

• Test ferritin and hemoglobin before supplementing—don’t guess.
• Ferritin <30 μg/L in athletes often warrants 30-60 mg elemental iron daily as ferrous bisglycinate.
• Take with vitamin C on empty stomach, away from calcium/coffee.
• No benefit—and potential harm—if iron status is normal.
• Re-test in 3 months; maintenance dosing is usually lower.

Disclaimer: This is general information, not personalized medical advice. Consult your healthcare provider for your specific situation.