Iron deficiency is much more common in athletes, particularly female athletes.

Menstrual blood loss is one factor, but we also use iron in muscle growth and repair.
This is not a problem if your dietary intake can keep up, but red meat is the best available source of iron and it can be hard to eat enough. Vegetable sources are harder to extract the iron from, putting vegetarians at more risk.
If your iron stores go low enough, you can end up anaemic. In general, athletes don’t get to this stage as they present with fatigue much earlier than that or are diagnosed on blood tests before symptoms start.
In the general population, iron stores of 20 – 30 are considered adequate. In athletes , we aim for 50 to account for the demands of training and everyday life.