Evaluating Iron Status in Endurance Athletes

In the previous part of this series, we looked at what iron does in your body, why so many runners (particularly women) deplete their stores, and which symptoms might indicate that you need to top up on this mighty micronutrient. Now let’s switch our attention to the best and most objective way to confirm if your ferritin and other iron markers are too low.

How do I know if I'm iron deficient?

I’ve worked with enough athletes to suspect when someone is low on iron, especially when they’re dealing with performance shortfalls, persistent fatigue, and some of the other symptoms we mentioned in part one without any other probable explanation. But I always like to have confirmation for my hunch by having my clients get bloodwork done. We always, always, always want to check our labs prior to supplementing, so we know that we are treating and supplementing correctly. 

Where can I get lab work done, and what labs should be checked?

Your primary care doctor can order labs to be drawn, whether it’s in-office or they send you to a lab. This option will likely be the most cost-effective if you have health insurance. Other options are to order your own labs from somewhere like Quest Diagnostics or Inside Tracker. Try to make sure you wait at least 48 hours after a race or hard training session before testing so you don’t skew the numbers. Once the panel has been drawn, you should get the results fairly quickly. 

There are several iron-related labs that can be checked. While ferritin is a common indicator of iron stores, it can give a false reading if you’ve been sick or under intense training or lifestyle stress. In which case, other markers can be useful. It’s also helpful to see the “whole picture” when it comes to iron labs <aka not just looking at one stand alone lab value>, so it’s important that you ask for CBC, iron panel and ferritin.

What should my ferritin level be as an endurance athlete?

Once you get the test results back, you’ll want to know whether your ferritin level is low, high, or just about right. The tricky thing is that the range is very broad – what’s considered to be “normal” at your doctor’s office is 10 – 120 ng/mL for females and 20 – 250 ng/mL for males. However, in running, cycling, swimming, triathlon, and other endurance disciplines, performance is usually optimized at or above 40 ng/mL, per a study by Japanese exercise scientists and other papers. At altitude, this can rise to more than 50 according to a study by Swiss researchers, as at higher elevation we need more oxygenated blood to sustain pace and power output. To make it even more complex, optimal ferritin levels can vary from person to person – Person A may feel great with a ferritin of 40 ng/mL, while person B might need theirs at 50 ng/mL.

My doctor said my ferritin level is ok, and my sports dietitian says it is low. Why is there a discrepancy?

There could be different parameters than your physician is currently not aware of – you’re probably the healthiest person they’ve treated all day, and labs within normal limits are typically a good sign. However, just because your iron levels are within normal limits for baseline health doesn’t mean that they’re optimized for endurance performance – the two goals are completely different. Your doctor isn’t wrong, but may only be looking at your ferritin and other iron markers through a lens for an average <sedentary to mildly active> adult. 

It’s this kind of contrast that shows why you might benefit from working with a registered dietitian or other specialist. Just having blood test data is only the first step – it’s what you do with the information that’s most important. So you need someone who has the right knowledge & experience to interpret the results, take into context your training and medical history, nutrition, and other factors, to help you come up with a plan. 

If you need a sports nutrition expert to analyze your labs & provide recommendations, take a look at our Featherstone Lab ConsultSimply answer some questions, attach your labs, and Meghann will analyze your lab work & send you an email with recommendations with in 10 business days.

How often should I check my iron status?

As levels of ferritin and other iron markers fluctuate over time, a one-off test might only give you a snapshot view of your body’s stores. Here’s a suggested frequency if you’re interested in ongoing testing that might enable you to keep tabs on your levels so you can address deficiency and even make pre-emptive changes if an initial panel shows a decline. 

Annually Once a year might be fine if you do not have a history of iron deficiency, and you have been feeling well during training and races.

Biannually: A test every six months might be better if you have a slightly low ferritin and are trying to increase with high iron food, are a female endurance athlete, or have the intention to increase training or head to altitude within the next 12 months.

Quarterly: Getting a panel every three months is advisable if you have a long history of iron deficiency, are currently supplementing trying to get an increase in ferritin, are vegetarian/vegan, see evidence of low energy availability, are continually training at high volume and intensity, struggle with ongoing fatigue/lethargy, or plan to train at altitude within six months.    

Check back next week, when we will share how to increase your iron and ferritin levels if they’re too low.

Do you need an expert to interpret your labs? The Featherstone Lab Consult is now available!

1. Yuki Kobayashi et al, “Attempt to Determine the Cut-Off Value of Serum Ferritin for Iron Deficiency in Male College Student Runners,” Journal of Nutritional Science and Vitaminology, 2020, available online at https://pubmed.ncbi.nlm.nih.gov/33132346. 2. German Clénin et al, “Iron Deficiency in Sports – Definition, Influence on Performance and Therapy,” Swiss Medical Weekly, October 2015, available online at https://pubmed.ncbi.nlm.nih.gov/26512429.

Disclaimer: The content in our blog articles provides generalized nutrition guidance. The information above may not apply to everyone. For personalized recommendations, please reach out to your sports dietitian. Individuals who may chose to implement nutrition changes agree that Featherstone Nutrition is not responsible for any injury, damage or loss related to those changes or participation.