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Iron and the Endurance Athlete

BY Craig David

Iron levels are a common topic among endurance athletes, and for good reason. Most would argue that iron has a significant influence in our performance- and it does. So how can we safely and effectively begin to advance our body's wellness & performance with this particular heavy metal?

Iron levels are a common topic among endurance athletes, and for good reason. Most would argue that iron has a significant influence in our performance- and it does. So how can we safely and effectively begin to advance our body’s wellness & performance with this particular heavy metal?

What Does Iron Do?

We should first understand a bit about how iron is working in the body. Iron (Fe) is the essential element of hemoglobin allowing our red blood cells to transport oxygen throughout the body. Consider iron the limiting factor in hemoglobin production. The classic indicator of low hemoglobin in relation to iron can result in iron deficiency anemia leaving you short of breath and exhausted. Pre-menopausal women, particularly those who exercise regularly, face a great risk of iron deficiency, or even anemia. Athletic, active males are also at high risk for Iron deficiency. Low levels of iron can leave you feeling physically tired and weak, impair mental function, and weaken the immune system.

Collecting Heavy Metal

Our body has a very distinct process of collecting and regulating the iron that’s circulating through our body. Iron is considered essential; that is our body cannot manufacture it and it must be consumed via diet or supplementation. Iron coming from dietary sources is absorbed in the small intestine. It has been documented that only about 10% of the iron consumed is actually retained and absorbed. That’s not much, making it all the more important to have a diet that focuses on variety and rotation of different iron sources. We lose iron through various avenues such as normal bleeding, menstruation, perspiration during high levels of endurance exercise, along with limitations of intake via various dietary practices.

Transportation Mechanisms

Once in the body, iron is transported in two ways. It can bind and travel by way of Ferritin or Transferrin, two different transport proteins (sounds nerdy, because it is). Ferritin binds and releases iron within the body as it’s needed. Free iron traveling through our bloodstream can also bond with Transferrin. This action is more of a protective mechanism of the body, preventing larger quantities of “free” iron from roaming and creating free radical damage. The unique relationship of iron bound to Transferrin appears in the making of new red blood cells. Transferrin essentially “docks and unloads” the iron within the red blood cell. This process is constant, and as red blood cells live 90-120 days, the process is even more important for athletes with high training loads.

Some Sources Are Better Than Others

A typical western diet provides both “heme” and “nonheme” iron. The “bioavailability” of iron (how well it’s absorbed) is a function of both it’s form and the other types of foods that either enhance or inhibit absorption. Heme iron is important due to its highly effective ability to be absorbed; more so than the non-heme form found in most plant sources. Heme iron accounts for somewhere around 10% of iron in our diets, yet can provide as much as a third of our absorbed iron due to efficiency. I know, that’s a lot of science, but important. Your heme sources from meats are optimal. If this isn’t an option for you, try combining as many of the non-heme sources as possible, with higher levels of vitamin C to increase chances of absorbing it.

The next option is oral iron. When appropriate, opt for the “ferrous” form vs the ferric iron. Ferrous has been noted to be more efficient with less side effects. A “chelated” form is also going to have an easier time being transported.

How to Increase and Maintain Healthy Levels of Iron

We know that “green leafy” vegetables and red meats are solid dietary sources of iron, but let’s take it one step further. How do we optimize our body’s ability to use Iron?

First we consider timing and pairing. A healthy dose of Vitamin C along with our iron containing food at lunch would be optimal. 1 orange or 2 clementines with 1-2 cups of sautéed spinach and/or kale plus your turkey sandwich makes for a home run. The other option would be to consider supplementing with a 150-200 mg Iron supplement later in the day, possibly with dinner. Additionally, get in a green leafy vegetable once per day at a given meal. For someone who’s severely deficient, red meat two to four times per week may be needed.

If you’ve been experiencing a lack of energy for an extended period of time, I’d recommend starting to wean to lesser quantities of caffeine. First, switch to decaf (if you don’t drink coffee, you’re ahead of the game– save it for the race) and work towards eliminating it and replacing with green tea. From there, you may start taking a dose of oral iron (capsule or liquid) plus 1500+mg of Vitamin C in the AM and then a second small dose in the PM to create a progression. This will help your body get back to a capacity to handle such training volumes; this could last from weeks to a few months. From there, you can then create a maintenance plan. In the process you’ll notice better sleep habits and better focus.

You may need to take a break. You are literally “smashing” and killing red blood cells as your run, otherwise known as “exercise-induced hemolysis.” In most cases, the body will eliminate the leftover iron via urine (another benefiting factor to anemia). We can’t sustain “peak fitness” for 12+ months. Realize your body is smart; it’ll eventually do what it has to in order to stay safe.

Consider periodizing your nutrition plan too. As intensity and output change, so should your nutritional intake. When working with athletes, this may be one of the biggest factors I see limiting an athlete’s performance. We most always work on nutrient rotation and adjusting caloric needs and fueling depending on the time of season, training volume, and goals.

Finally, get a blood test done. This is possibly the most important; if it’s been 6 months since you’ve last had one and things just don’t seem right, it’s probably time to do it again. Environmental conditions, training and dietary conditions all affect how our body’s metabolic functions either improve or become suppressed. We’ve seen a lot of success with athletes here in Boulder by implementing a blood analysis that looks at certain Biomarkers within a person’s blood profile. If we know this information we can then decipher how all the above suggestions can better be aligned to improve an athlete’s general wellness, greater immune support, and performance at the same time.

It is critical that iron levels be kept sufficiently high to stay healthy. This is especially true for all endurance athletes. Through a combination of the right foods at the right time you can keep your iron levels high to support your daily training.


Mayo Clinic. (2022, January 4). Iron deficiency anemia. Retrieved from

Rowland, T. (2012, January 20). Iron Deficiency in Athletes: An Update. Retrieved from

Ishibashi, A. et al. (2020). Effect of low energy availability during three consecutive days of endurance training on iron metabolism in male long distance runners. Retrieved from

Santiago, P. (2012, May 2). Ferrous versus ferric oral iron formulations for the treatment of iron deficiency: a clinical overview. Retrieved from

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About Craig David

Craig David lives in Boulder, CO. where he is a Certified Sports Nutritionist. Born and raised in Colorado, Craig grew up surrounded by the mountains, a small town atmosphere, farming, skiing and aviation. Upon graduation, Craig received a B.S. in Health and Exercise Science & Nutrition for Colorado State University. His career highlights include an internship at the White House Athletic Club in Washington, D.C. training some of the nation’s finest. He also has extensive experience in performance gear testing, horizontal power testing, and cardio pulmonary testing. Today you’ll find Craig speaking to high school and collegiate sport teams, working with the local SWAT teams, designing custom nutrition programs for the high-end professional athlete to engaging the average person in a corporate wellness education seminar. Join him in the pursuit of a healthy lifestyle! Find him at