REF-1419 · Mettler & Zimmermann, 2010 · European Journal of Clinical Nutrition · Paper · PubMed

Should I take iron just in case?

In 170 Zürich marathon amateurs, under 2% of men had depleted iron stores but 15% had ferritin above 200; 28% of women were depleted. The authors: take iron only if a test shows a deficiency.

Main caveat: Abstract only; the full text was not open.
moderate evidenceMeasured on recreational to trained athletes

Mettler and Zimmermann (ETH Zurich) measured iron status in 170 recreational runners (127 men, 43 women) taking part in the Zürich marathon, motivated by the wide use of iron supplements by athletes and the long-term risks of overload.

Iron depletion was ferritin below 15 µg/L, functional iron deficiency an sTfR:log(ferritin) index of 4.5 or more, and — after excluding runners with raised CRP — iron overload ferritin above 200 µg/L. Depletion was found in 2 of 127 men (1.6%) and 12 of 43 women (28.0%); functional deficiency in 5 men (3.9%) and 11 women (25.5%).

Body iron stores were higher in men (P < 0.001); median male ferritin was 104 µg/L with an upper limit of 628 µg/L; and 19 men (15.0%) but only 2 women (4.7%) had ferritin above 200 µg/L. Male sex, not age, predicted higher ferritin.

The authors conclude that excess body iron may be common in male recreational runners and that supplements should only be used if iron tests show deficiency.

Our reading: the base's evidence for testing first in exactly its users — depletion is a women's problem far more than a men's in this sample, and taking iron "to be safe" would, for many men, add iron to stores that are already high. It cannot show that supplements caused the high values, and when blood was drawn relative to the race matters (REF-1414).

Protocol

Participants: n = 170 recreational runners (127 men, 43 women) participating in the Zürich marathon.
Definitions: iron depletion plasma ferritin (PF) <15 µg/L; functional iron deficiency sTfR:log(PF) index ≥4.5; iron overload PF >200 µg/L after excluding subjects with elevated CRP.
Measures: plasma ferritin, soluble transferrin receptor, CRP; body iron stores calculated from the sTfR/PF ratio; age and sex as predictors.
Not in the abstract: timing of the blood sample relative to the race, supplement use, diet, training volume, transferrin saturation, genetic testing.
Funding and interests: PubMed lists "Research Support, Non-U.S. Gov't" without naming the funder; no conflict-of-interest statement in the abstract record.

Key Results

Men (n = 127)Women (n = 43)
Iron depletion (ferritin <15 µg/L)2 (1.6%)12 (28.0%)
Functional iron deficiency (sTfR:log ferritin ≥4.5)5 (3.9%)11 (25.5%)
Ferritin >200 µg/L, raised CRP excluded ("iron overload")19 (15.0%)2 (4.7%)
Median ferritin104 µg/L (upper limit 628)not given in the abstract
Body iron stores (from sTfR/PF) were significantly higher in men than in women (P < 0.001).
Predictors: male sex (P < 0.001), not age, predicted higher ferritin.

Mechanisms

Measured: a wide ferritin distribution in male amateur runners reaching 628 µg/L, with depletion rare in men and common in women.
Authors' interpretation: although athletes widely take iron supplements to improve performance, excess body iron may be common in male recreational runners; overload should be avoided because of possible long-term adverse health effects.
Inference: ferritin is also an acute-phase protein and rises for days after a marathon (REF-1414); runners with raised CRP were excluded, which removes part but not all of that effect, and the abstract does not say whether blood was taken before or after the race.
Inference: a ferritin above 200 µg/L has causes other than iron intake, and whether it means iron overload is a clinician's question; this study did no further work-up.

Practical Application

Should I take iron just in case? In 170 Zürich marathon amateurs, under 2% of men had depleted iron stores but 15% had ferritin above 200; 28% of women were depleted. The authors: take iron only if a test shows a deficiency.
The source for "no iron without a blood test": the base's rule in SYNTH-06 (practice until now) has a direct finding behind it for recreational runners: deficiency and excess both occur, unevenly by sex, and only a test tells them apart (B+, from the abstract).
Men: in this sample a man was far more likely to have ferritin above 200 than depleted stores (19 vs 2 of 127; age did not predict ferritin, and the age range is not in the abstract); not from this paper, the base's own practice: a high ferritin goes to a clinician, not to the assistant.
Women: more than a quarter of female runners were depleted, so testing matters in both directions (REF-573 for heavy periods).
What it does not show: that supplements caused the high values, any health outcome, or whether these ferritin levels reflect body iron rather than inflammation in every case.

Limitations

Abstract only; the full text was not open.
Single sample; its timing relative to training and the race is not reported in the abstract.
Overload by ferritin alone, with raised CRP excluded; no transferrin saturation, liver measure or genetic test in the abstract.
Supplement use, diet and alcohol are not reported in the abstract, so causes cannot be assigned.
Few women (43); Swiss runners in 2010.
Funding and interests: funder not named in the record; no conflict statement in the record.
How this entry was checked and changed
Why this level

(from the abstract) — a cross-sectional study with at least 100 participants (rubric B+); supplement use, diet and when blood was drawn relative to training or the race are not reported in the abstract