Nutrient Timing Guide to Optimize Iron Absorption
By Corrine Malcolm, CTS Ultrarunning Coach
As an endurance athlete it’s likely that you’ve had blood work done sometime in the past. Terms like “CBC” (complete blood count), serum ferritin, hemoglobin, and hematocrit might ring a bell. If you are a female athlete you are likely all too familiar with iron deficiency (ID), or anemia. In fact, ID is alarmingly prevalent in endurance athletes, with nearly 60% of all female athletes and 4 to 50% (Hinton, 2014) of all male athletes experiencing some form of iron deficiency in any given year.
It’s important to mention that there are two types of ID, anemic and non-anemic. Non-anemic ID presents with a drop in ferritin but normal hemoglobin levels. This is generally an early sign of having insufficient iron. Non-anemic ID can progress to anemic ID when low ferritin reduces hemoglobin synthesis and leads to a decrease in red blood cell production and full blown anemia. Neither form of ID is good for athletic performance. What that means is you can have normal iron levels in every other aspect except your serum ferritin and experience a noticeable decline in performance. This is because low ferritin, or low stored iron, impairs your aerobic energy pathways. Essentially, you can deliver the oxygen your body needs but you have an impaired ability to use that oxygen, forcing you into an anaerobic state at lower intensities (Hinton & Sinclair, 2007). Or rather, low ferritin lowers your lactate threshold, which can make once manageable intensities feel significantly harder to maintain.
What has changed over the past decade is our understanding of how exercise and nutrient timing are highly intertwined. When you exercise your body creates inflammation, or specifically an inflammatory cytokine called interleukin-6 (IL-6). IL-6 is one of the main regulators of exercise released hepcidin that functions as the controller of iron absorption in your body. When hepcidin levels increase, iron absorption decreases. Hepcidin levels peak 3-6 hours after exercise, which means taking an iron supplement on an empty stomach, or consuming an iron-rich meal immediately after a workout, is not likely the best plan.
What if you suspect iron deficiency?
As always, the first step should be talking with your health care provider and getting a CBC and serum ferritin test. Doing so will help identify if the symptoms you are experiencing are linked to ID, and that first test can be used as a baseline for future testing.
The next phase in your plan of attack for better iron absorption should be to make sure you optimize your iron intake through your diet. This means eating quality heme (found in animal products) and non-heme (found in fortified and plant products) iron containing foods at times well removed from your hard workouts. Although rewarding your hard effort with a big burger sounds like an excellent idea, your body’s post-workout inflammation is high, which decreases your ability to absorb the iron from that burger. In getting iron from food sources and dietary supplements, timing is key.
How to best utilize iron-rich foods
- Consume iron rich meals, especially those that contain heme iron at times well removed from hard workouts, and on easier days, to optimize iron absorption while body inflammation is lower.
- If you’re not a vegetarian, pay especially close attention to heme iron containing food sources as heme iron is absorbed at a rate of 7-35% while non-heme iron is absorbed at a lower rate of only 2-20%.
- If you’re not a vegetarian pair nonheme iron sources with meat, fish, or poultry to increase the absorption rate of the nonheme iron.
- Consume iron-rich meals with acidic foods rich in Vitamin C, such as citrus, tomatoes, and red peppers.
- Avoid consuming iron-rich meals with calcium, phosphorous, zinc, or magnesium as they compete for the same binding sites as iron.
- Avoid consuming iron-rich meals with eggs, as they contain a compound that has iron-binding capacity and can inhibit iron absorption by as much as 28%. The same can be said for drinks like coffee and tea that are high in tannins.
- Avoid consuming iron-rich meals with foods high in fiber, as they can decrease the amount of nonheme iron absorbed. However, you can counter this by eating fiber with a food that naturally enhances iron absorption, like citrus that contains Vitamin C.
- Focus on foods that are rich in heme or non-heme iron such as beans, shellfish, dark leafy greens, dark chocolate, lentils, pumpkin seeds, oats, fortified cereals, tofu, beef, and molasses.
What about supplements?
- Take your iron supplement every other day. Research suggests you’ll see a rise in your hepcidin levels for up to 24 hours after ingesting an iron supplement. The thought is that spacing your supplement intake to every other day increases your potential for iron absorption.
- Delay your iron supplement intake at least 6 hours after you are done exercising. Hepcidin levels are thought to peak 3-6 hours post exercise. If you are a morning exerciser, focus on iron after lunch or before dinner. If you exercise in the afternoon, focus on taking your iron when you wake up.
- Eat a moderate carbohydrate snack before and during workouts lasting 90 minutes or longer. Ingesting carbohydrates has been shown to blunt post exercise IL-6 levels which should modulate the hepcidin response as well. (*Badenhorst link, 2015a)
- Eat a carbohydrate- and protein-rich snack after exercise. It has been shown that increasing muscle glycogen stores and avoiding putting your body into a glycogen sparing state can lower your post-exercise IL-6 and hepcidin response.
- Supplement with Vitamin D3 + K2. Vitamin D3 has been shown to reduce hepcidin levels in healthy individuals, while vitamin K2 has been shown to synergistically work with vitamin D3 to blunt the inflammatory response and prevent the risk of possible vitamin D toxicity.
For many people, consuming iron-rich foods is enough to maintain adequate serum ferritin levels. But even if you are one of those people, timing your iron consumption can help optimize iron levels, and subsequently athletic performance. If you find you and your physician determine you would benefit from an iron supplement, do yourself a favor and time your supplementation to optimize absorption.
Corrine Malcolm is a CTS Ultrarunning Coach and a professional runner for Salomon. She has a B.S. in Health and Human Performance, and she’s a Masters candidate in Biomedical Physiology. In 2016, Corrine won the USATF 50 Mile Trail Championships and represented the US at IAU Trail Running World Championships.
Hinton, P.S. 2014. Iron and the endurance athlete. Appl. Physiol. Nutr. Metab.
39(9): 1012–1018. doi:10.1139/apnm-2014-0147. PMID:25017111.
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Hinton, P.S., and Sinclair, L.M. 2007. Iron supplementation maintains ventilatory
threshold and improves energetic efficiency in iron-deficient nonanemic
athletes. Eur. J. Clin. Nutr. 61: 30–39. doi:10.1038/sj.ejcn.1602479. PMID:
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Comments 20
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In addition to exercise increasing hepcidin levels, doesn’t hepcidin level increase throughout the day, falling again while sleeping? As such, it seems the best time to have high iron meals and to take iron supplements is in the morning. Even iron intake immediately after morning exercise will beat the diurnal and exercise induced increases in hepcidin.
Thank you for the info on post workout hepcitin levels! This is one aspect I was still ignorant of.
I am an elite level powerlifter on a low-dose TRT program. My hematocrit and hemoglobin tend to rise to the upper range limits and standard protocol throughout the industry is to then have the patient donate blood when this happens.
Unfortunately this errored practice puts those patients at the risk of ID. As, they DO NOT typically check iron or ferritin levels prior to ordering a donation or phlebotomy.
Literally all clinics and PCPs run a basic CBC. However, neither group typically ever orders iron or ferritin levels unless the CBC shows anemic values! (Crazy!) I was non anemic Iron deficient.
After donating three times in the same year, this protocol crashed both my iron and my ferritin levels. I have since suffered from fatigue so severe I could not complete a 40 hour work week and had to take six months off of any type of training at all.
I have now been doing everything I can (for the last eight months ) to restore those levels…
A Ferritin test is the easiest and most accurate test. But, if you do not insist that they check it, they generally will not. (Even when I was referred to an oncologist for my symptoms…)
Thx again for the timing info.
Great article!
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Great piece Corinne, ID and non anemic low iron is rampant in endurance athletics, especially among females. With so many youth sports becoming year round endeavors with intense training schedules, I believe much of athletics in general need to wake up to this one. Your points on hepcidin and timing are excellent and in my opinion, are missed in most when they try to wing this. Difficulty for many is that many primary care docs are unaware of the hepcidin and timing issues as well and many still downplay supplementation or dietary modification unless ferritin levels are below the standard lab reference range of 13ng/mL or if an anemia is present. Athletic performance is often hampered well above these values.
awesome article, It really helps me as a cyclist!! thank you.
In the past there was thinking that only women should supplement iron intake. Even now it is not part of multi – vitamin supplements for men. Seems like there was a cardiac reason. Has current thought gotten away from that?
Interesting how ingesting a carbohydrate snack before and during extended periods of exercise blunts the post inflammatory response. Piece of fruit, or a sports drink?
Thanks for the great summary? The role of phytic acid from tea, coffee and soda is very significant indeed right?
Wow, great article! Specific recommendations that are actionable– love it! Thanks Corrine 🙂
Dealing with these issues since going fully plant-based. Learning about iron absorption was key to feeling better on and off the bike!
Hi! Great info. Would love some actual meal suggestions for 3-6 hours post workout.
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And with all that to think about before eating, let me throw one more thought into the mix, some foods (usually processed fast foods) cause systemic inflammation as well immediately after eating them and last 4-5 hours.
This has to be an impressive and detailed article … hmmm… pity that it’s way over my level of understanding. Citrus, tomatoes, red peppers, eggs, coffee and tea are about the only things I recognized .. LOL 🙂
Hi Sergio,
Sorry it was complicated, here are the key points. Even if just your ferritin is low (all other blood values you normal) your athletic performance can suffer. Timing is key, getting iron from food sources is really hard, but if it’s safe for you to supplement it’s easier to take those supplements at least 6 hours after hard workouts to get the iron you need. Hope that helps!
If I had to think about all that stuff before eating, my head would explode. Nice article though.
I agree completely! That’s why I went to my doctor to make sure it was safe for me to supplement. And now I just worry about not taking it with my coffee/tea and spacing it away from my workout.
Great article. Nutrition is a complicated topic
Kathy