Iron supplements, ferritin levels, and VO2max gains in athletes

Red blood cells in the style of a hand-drawn sketch

There’s a new study out this month on iron supplements for athletes with low ferritin. The study, published by Anja Neža Šmid and colleagues at the University of Ljubljana in Slovenia, is a meta-analysis, meaning it pooled data from several different randomized trials that took athletes, assigned them to either a placebo group or an iron supplement group, then measured the difference in ferritin levels between groups after the study’s conclusion.

The results of this meta-analysis are some of the strongest evidence that I’ve seen that support the notion that athletes with ferritin levels circa 20 ng/mL will benefit from an iron supplement. However, I wanted to write up this post because that’s actually not how the authors of the study interpret their own results!

Here’s what Smid et al. say in the abstract:

Increase in serum ferritin concentration after [oral iron supplementation] was evident in subjects with initial pre-supplementation serum ferritin concentration ≤12 µg/l [ ng/mL], while only minimal, if any effect, was observed in subjects with higher pre-supplementation serum ferritin concentration.

Šmid et al 2024

How can I justify the benefits of iron supplementation at 20 ng/mL, while the authors cite a cut-off value of barely half that level? Well, it all comes down to the way you analyze the data.

Here’s the bottom line up front: when treating ferritin level as a continuous number—which it is—the study’s data clearly show that runners with ferritin levels of around 20 ng/mL or less will experience significant increases in ferritin and gains in VO2max when taking an iron supplement over the course of 6–8 weeks.

Read more

Notes on Randall Wilber's "Altitude Training and Athletic Performance" for runners

If you are interested in altitude training, Randall Wilber’s book “Altitude Training and Athletic Performance” is a fantastic read. I apologize for the lack of posts recently, but I’m recovering from arthroscopic hip surgery last week and am not up for doing a whole lot of sitting (in fact, I’m typing this out standing at ... Read more

Ferritin, hemoglobin, and iron deficiency in distance runners

Attention readers! This article is officially outdated! I've released a new and updated article on iron deficiency in runners that is much more complete.   >>Click here to check out the updated article!<< When a distance runner begins to struggle early on in workouts and races, suffers from excessive fatigue, and often feels there's no "gas ... Read more

Did you know I have a book? Check it out here!