Hemoglobin levels and cardio capacity

Question

I am a blood donor, giving about 0.5L blood approx every 3-4 months. Last time I was in to give blood, I had a short chat with the nurse about Hgb levels in blood, recuperating after the donation and it got me thinking...

I was out taking a jog the next day and it was MUCH harder than a couple of weeks ago, I was short of breath almost directly after 3-4 km. Since my O2 carrying capacity had decreased by a quarter or so, it was understandable. I know it'll take a bit of time to recover the iron that was lost during donation, and I adapt my diet accordingly.

What I wonder is:

Q1: is an optimal level of iron/Hgb that is dictated by my metabolism, or can I increase my Hgb level beyond what it was earlier by adapting a more iron-rich diet?

To give an example, my Hgb levels are between 140-150 g/L normally. Having lost a quarter of that amount recently, can I go beyond that range by adapting an iron-rich diet, or will I just not take up more iron from my diet once I get back to my "normal" level?

Q2: As a follow-up question; does more iron equate higher cardio capacity? I suspect that it's not that simple...

Please note that I'm looking for information with scientifically relevant references and not urban legends or rumours that are perpetuated in gyms.

Answer 1

Q1. The iron supplementation in the nondeficient state does not improve performance. That is, taking more iron into the body will not increase your hgb level beyond what it was earlier. (Herbold NH, Visconti BK, Frates S, et al.: Traditional and nontraditional supplement use by collegiate female varsity athletes. IntI Sport Nutr Metab 2004, 12:586-593.). In another study it was indicated that although iron supplementation can raise serum ferritin, increases in ferritin unaccompanied by increases in hemoglobin concentration have not been shown to improve endurance performance (Garza, D., et al. The clinical value of serum ferritin tests in endurance athletes. Clinics in Sports Medicine, v. 7, p. 46-53, 1997.). There are other ways of increasing your hemoglobin level such as high altitude (2700m-3500m), EPO, blood doping (last two are not recommended and forbidden) etc.

Q2. Hemoglobin has an oxygen-binding capacity of 1.34 mL O2 per gram and it contains 4 heme groups each with one iron atom that are able to bind one molecule of oxygen. That is, if you have high hgb level you can bind more oxygen but it does not guarantee you to have higher cardiorespiratory capacity because iron and hgb are not the only factors that affect cardio performance, there are so many. However, having high enough level of hgb and iron may help cardiorespiratory performance.