When should a runner take iron?

McCormick and colleagues (Perth, with the ETH Zurich isotope group) asked whether the time of day of an endurance session changes post-exercise inflammation, hepcidin and iron absorption. Sixteen endurance-trained runners (10 men, 6 women) with ferritin below 50 µg/L ran 90 min at 65% of the velocity at VO2max in the morning or in the afternoon in a crossover design.

Thirty minutes after the exercise and control conditions of each trial, they took an iron-fortified drink labelled with a stable iron isotope with a standardised meal, serving as breakfast or dinner; erythrocyte incorporation 14 days later gave absorption.

Exercise raised IL-6 (by 4.938 pg/mL, P = 0.006) and, 3 h after exercise, hepcidin (by 0.380 nM, P < 0.001); in the afternoon trial hepcidin showed a diurnal rise at rest (0.55 nM, P = 0.007) before rising a further 0.68 nM from before the run to 3 h after.

Even so, fractional absorption was greatest at breakfast after the morning run — greater than the rested condition (0.778%, P = 0.020) and than dinner in the morning-run trial (0.672%, P = 0.011). The authors suggest a transient mechanism in the acute post-exercise window that promotes absorption despite rising hepcidin.

Our reading: with REF-1421 (iron in a meal 2 h after a long run absorbed 36% less) it turns PHYS-36's "one isotope study each way" into two entries that differ in timing — 30 min after a moderate morning run vs 2 h after a long one — rather than flatly contradicting each other.