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The Complexities of Iron Repletion in Athletes

Updated: Jan 30, 2020

For women, it’s not uncommon for us to be iron deficient, what with menstruation and monthly blood (and iron) loss. Yet for both female and male runners, their risk of iron deficiency is increased due to:

  • High-impact training that damages red blood cells [a.k.a., foot-strike hemolysis (literally crushing blood cells when the running foot strikes the ground)].

  • High-intensity training that increases blood loss from the gut.

  • Low-energy availability that restricts how many calories are consumed and therefore fewer nutrients (like iron) and carbohydrates (read on below).

  • Sweating.

  • Inflammation.

So when an athlete's blood work is returned and an iron profile is suboptimal, developing an iron repletion plan becomes hairy fast.

Why? Read on.

The Lingering Effect of Training: My Obsession with Hepcidin

Exercise causes stress on the body that results in many feedback loops, one of which being the release of hepcidin—an amino acid peptide produced by the liver that acts as the primary iron regulator in the body.

Once circulating in the bloodstream in high levels, hepcidin reduces iron absorption from the gut and inhibits iron recycling that otherwise would have occurred. Depending on the intensity of the training sessions, this nasty cycle of iron hate peaks around 3-6 hours after completing a workout and remains at higher-than-normal levels for 6-12 hours overall.

It's not uncommon for athletes to train twice daily—in the morning and again in the afternoon—so finding a consistent time for iron supplementation during waking hours is impeded by hepcidin.

Low-Carbohydrate Availability May Worsen the Impact of Hepcidin

It gets worse.

Badenhorst et al. (2015) found that in the presence of a low-carbohydrate diet (and when compared to a high-carbohydrate diet*) and bouts of exercise in well-trained male recreational endurance runners and triathletes, hepcidin levels were higher than normal after having completed a workout and remained higher even after recovery.

Although the above study only considered a 24-hour period, an iron deficient athlete may require some additional dietary education to increase their carbohydrate intake while taking iron pills.

*Badenhorst et al. (2015): The high-carbohydrate diet provided 10 grams of carbohydrate per kilogram body weight (i.e., the equivalent to a triathlete carb loading in the days leading up to a race) whereas the low-carbohydrate diet provided 3 grams of carbohydrate per kilogram body weight.

Chocolate Milk and the Muscle-Protecting Bedtime Snack

In an earlier post, I lauded the benefits of dairy as a bedtime snack to protect muscles while an athlete sleeps.

So if a swimmer (or any athlete) is training in the morning and the late afternoon, iron supplementation makes sense at night when hepcidin levels should in theory be at their lowest during waking hours.

Unfortunately, bedtime iron supplementation and dairy aren’t always the best combo. Here’s why:

  • Calcium is rampant in dairy (usually a good thing!).

  • Calcium and iron compete for absorption in the gut.

  • Milk contains phosphates and chocolate milk contains higher levels of oxalic acid, both of which further reduce iron absorption.

  • So popping iron pills while enjoying dairy as a bedtime snack isn’t the best way to maximize iron absorption.

Although I’m still a huge fan of dairy products, it’s more about shifting when you consume these nutrient-dense options throughout the day while repleting iron levels rather than foregoing dairy completely.

The Nasty Side of Supplementation: Weird Trips to the Bathroom

Iron supplementation in the form of ferrous sulfate is the go-to, yet ferrous sulfate is closely linked to constipation, diarrhea, nausea, and vomiting. Symptoms like these can result in poor compliance, so an athlete may reduce or forego their iron pills—meaning that iron deficiency continues.

Constipation relief with ample fluid and insoluble fiber intake are key to keep the bowels moving along (exercise is also recommended, but I’m assuming the athlete is frequently moving). If constipation persists, consider a stool softener.

Black stools are a sign that supplementation is working, but it’s always a good idea to warn an athlete about this prior to beginning iron pills.

Nausea and vomiting are also common, but these symptoms tend to be reduced when pills are taken with a meal or are provided in an enteric-coated form.

Take-away Message: Be Creative When Creating an Athlete’s Iron Supplementation Plan

  1. For athletes training more than once daily, supplement in the morning (before the first session begins) or immediately after the first session as to beat the eventual high circulating levels of hepcidin. Granted, if supplements are taken at breakfast time then be aware of coffee, tea, fiber, and/or calcium intake.

  2. Supplement during off days and/or when only one training session occurs: When compliance is low, focus the athlete’s attention on key days and when hepcidin levels are lowest.

  3. As always, opt for a third-party certified brand of supplements to minimize the risk of athletes failing a drug test and to ensure the correct dosage and ingredients exist within the product. Here’s one of my favorite brands.

  4. Increase an athlete’s fluid and fiber intake to counter constipation.

  5. Ensure adequate carbohydrate intake while repletion is occurring.

  6. When swallowing an iron pill:

  • Avoid calcium, bran, phytic acid, oxalic acid, fiber, tea, and tannins (e.g., coffee): All of these reduce iron absorption, so maximize dairy and fiber throughout the day—not while swallowing iron pills.

  • Consume vitamin C: It promotes iron absorption, so a swig of orange juice can help. Or, consider a smoothie that includes frozen papaya and whey protein powder (neither dairy nor plant-based dairy alternatives).


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