REF-1552 · Fensham et al., 2022 · International Journal of Sport Nutrition and Exercise Metabolism · Paper · PubMed

Do two sessions stack iron-related markers?

In 16 fed elite male rowers, IL-6 and hepcidin held a plateau across a second session 2.5 h later, no extra rise. No single-session arm, markers only, submaximal rowing.

Main caveat: Abstract only. No copy in PubMed Central or Europe PMC. Intensity, diet, baseline iron and the exact statistics of the comparison were not read.
limited, mixed evidenceMeasured on elite athletes

Sixteen elite male rowers did two trials a week apart, in random order, one with a high-calcium (1,000 mg) and one with a low-calcium (<50 mg) pre-exercise meal. Each trial was two submaximal 90-min rowing ergometer sessions 2.5 h apart, with blood at baseline, before exercise, and at 0, 1, 2 and 3 h after each session.

IL-6 peaked at about 7.5-fold over baseline 2 h after the first session and hepcidin at about threefold 3 h after it (both p < .0001). After the second session both stayed above baseline with no additional step up: the comparison of 2 h after the first against 2 h after the second gave p = 1.00.

Pre-exercise calcium went with slightly higher hepcidin at all time points (p = .0005) and had no effect on IL-6 (p = .27). The authors credit adequate nutritional support, and advise taking iron around morning exercise before hepcidin climbs. Our reading: a useful check on the assumption that two sessions always compound.

But the plateau is defined against the rowers' own earlier values and not against a day with one session, and neither the diet nor its adequacy was varied in the part of the design that bears on the double.

Protocol

Who: 16 elite male rowers. Age, iron status and training load are not in the abstract.
Sessions: two 90-min submaximal rowing ergometer bouts, 2.5 h apart. Target intensity is not printed.
Meals: high (1,000 mg) or low (<50 mg) calcium before exercise. Carbohydrate, energy and iron content are not in the abstract.
Sampling: baseline; pre-exercise; 0, 1, 2, 3 h after each session. Two trials separated by a week.
A timing question: the abstract places the hepcidin peak 3 h after the first session while the sessions were 2.5 h apart, which on a plain reading would fall inside the second session. The abstract does not resolve this; the paper's own timeline was not read (our reading).
Funding and interests: not in what was read.

Key Results

MeasureResultp
IL-6 peak, 2 h after first session, relative to baselineabout 7.5-fold< .0001
Hepcidin peak, 3 h after first session, relative to baselineabout threefold< .0001
2 h after first vs 2 h after second session (one p printed, read here as both markers)plateau, no additive rise1.00
Pre-exercise calcium on hepcidin, all time pointsslightly higher with calcium.0005
Pre-exercise calcium on IL-6no effect shown.27
"No additive rise" is not "no cost." Both markers remained elevated, and a p of 1.00 is no equivalence test.
No comparator. With no single session arm, hepcidin that would have come down without a second session could have been held up by it; this design cannot tell (inference).
Different question from Ronsen. Ronsen's IL-6 was higher against a single bout after a 3-h gap, at 75% of VO2max; here the contrast is second against first within a double. They do not test the same thing.

Mechanisms

Measured: the blood time course of IL-6 and hepcidin, and a small calcium effect on hepcidin.
Authors' interpretation: good feeding allows two sessions in close succession without amplified responses. This was not tested: nothing in the abstract varied feeding except calcium.
Not reported in the abstract: iron absorption, ferritin or other iron status, haemoglobin mass, muscle glycogen, intensity beyond "submaximal", performance.

Practical Application

Do two sessions stack iron-related markers? In 16 fed elite male rowers, IL-6 and hepcidin held a plateau across a second session 2.5 h later, no extra rise. No single-session arm, markers only, submaximal rowing.
Good for: tempering the idea that a second submaximal session always compounds the hepcidin response, in fed elite men.
Good for: the authors' timing point, which agrees with iron-timing work in the base: iron taken around a morning session, before hepcidin rises, is their suggestion and was not tested here.
Not good for: concluding doubles are free of cost for iron. Hepcidin stayed above baseline, and the abstract reports nothing on absorption or stores.
Not good for: women, runners or hard doubles. All three are absent.
Not good for: calcium advice. The effect was small, the authors ask for further work, and no iron or performance outcome depends on it.
Not from this paper: spacing calcium-rich foods and iron intake is general nutrition practice; this trial measured hepcidin, not absorption.

Limitations

Abstract only. No copy in PubMed Central or Europe PMC. Intensity, diet, baseline iron and the exact statistics of the comparison were not read.
The randomised factor is calcium. The result the base wants, on the double, comes from a time-course comparison inside each trial, and not from a randomised contrast.
No single-session or rest control, so natural diurnal or time-course change in hepcidin cannot be separated from the second session (inference).
One comparison point. The p = 1.00 is for 2 h after each session; the second session's hepcidin comes on a rising or plateauing curve from the first.
Elite men only, in a low-impact sport.
"Adequate nutritional support" is the authors' phrase and was not an experimental variable on what was read.
How this entry was checked and changed
Why this level

(from the abstract) — a crossover of this size earns B+ only for its randomised question, and that is calcium. For the question in this entry it is an uncontrolled comparison across time points, with blood markers as the only outcome, and no copy in PubMed Central or Europe PMC could be read