Here's my take on the blood donation issues.

Your blood is made up of fluid (plasma) and cells (red blood cells, white blood cells, etc - called "formed elements"). The red cells carry the oxygen. One of the physiological adaptations from training that your body accomplishes is that it increases the total blood volume in your body - this enables it to be better equipped to supply the demand for blood when you're exercising and especially when you're exercising in the heat and blood needs to be shared by the vital organs, the exercising muscles and the skin (for cooling). "Runners anemia" is the condition where your body has increased the blood volume in a slightly disproportionate manner by increasing the plasma more than the formed elements. This is a good thing because you still have plenty of red blood cells to transport oxygen, but your blood viscosity is slightly thinner which makes it easier to pump.

Now - if you go run AFTER blood donation, you're running with a lower blood volume and this is not good -- your body still has the same demands for blood flow, only there's less of it to pump... so the heart has to pump harder (faster) to supply the demand.
Running BEFORE donation might be a problem IF you fail to rehydrated any lost fluids during the run. If you ran and sweated, and didn't rehydrate, then the lightheaded feeling might have been due to a further reduction in your total blood volume (plasma moves into your tissues at a greater rate when you exercise - so you may have a slightly lower blood volume immediately after exercise).

Could you temporarily "fix" your "runner's anemia" by dehydrating before going to give blood? Possibly.... but you need to be sure that what you're dealing with truly IS runner's anemia.

Just my 2 cents worth. - Janet

------------------
Treat the cause, not just the symptom... http://www.runningstrong.com[/URL" target="_blank">