Iron absorption may be inhibited after a long run...

Researchers at Florida State University had well-trained women do one- and two-hour runs and then measured their levels of hepcidin, a hormone produced in the liver that reduces iron levels in the blood. Hepcidin levels spiked after the runs, especially after the two-hour run, and then iron levels in the subjects' blood dropped.

The implications of this are that if you are trying to increase your iron intake for whatever reason, you might be more successful in doing so by consuming supplements or iron-rich foods at a time other than the several hours after a hard workout. Do it earlier or much later in the day, so you're not fighting against this absorption-blocking effect.