Can a Hard Workout Block Iron Absorption?
March 29, 2012
A lot of endurance athletes, particularly women, struggle with low iron. As a new study in the International Journal of Sport Nutrition and Exercise Metabolism explains:
The increased incidence of iron deficiency in female endurance athletes is thought to be the result of low dietary iron intake in this population, losses of iron in menstrual blood, sweat iron loss, and gastrointestinal blood loss.
But there's another possible reason, which is what this study (from researchers at Florida State) is all about. In brief: exercise produces inflammation (as evidenced by elevated levels of cytokines in the blood); inflammation causes increased production of hepcidin (a hormone produced in the liver); and hepcidin reduces iron levels in the blood.
To test the hypothesis that this sequence of events could contribute to iron problems in female athletes, the researchers had 12 endurance-trained women perform a one-hour run and a two-hour run, while they measured various blood parameters (cytokines, hepcidin, iron levels). Here's how hepcidin levels responded in the hours after the run:
As you might expect, a spike in inflammatory cytokines occurred right after the runs (so it preceded the spike in hepcidin). And there was a corresponding dip in serum iron levels around nine hours after the run (following the spike in hepcidin). All of this supports the sequence of events outlined in the hypothesis.
So what does this tell us? If you're supplementing iron, or consciously choosing iron-rich foods to keep your levels up (which is likely a good idea for many female athletes), you should try to time it so you're not taking the supplements in the six hours after a hard workout. Do it earlier or later in the day, so you're not fighting against this absorption-blocking effect.
One other note: when they broke down the results individually, five subjects had very large hepcidin responses, and seven had small or moderate responses. So the advice above probably doesn't matter for more than half of you, and might matter a lot for the rest. We don't know which half is which -- but if you suffer from perennially low iron levels, we can take an educated guess.
[Many thanks to Trent Stellingwerff of the Canadian Sport Centre Pacific for pointing this study out!]