I was wondering if anybody here knows anything about the effects different levels of CO2 have on the ph-level of the blood and this effect on health etc.

If you run a marathon, there will temporarily be more CO2 in the blood so i would think this would affect the ph-value of the blood making it more acidic or alkaline depending on how it reacts in the blood.

So what are the health-effects of this and what could you do to compensate any possible negative effects from it?

The body has a built in buffer system to make sure blood has the same ph at all times. Co2 in absorbed into the blood stream from cellular respiration and creates a bunch of ions. The difference in pressure of the co2 in the alveoli and your blood stream have it transport across the membrane and out of your body when you exhale. what goes in must go out

So no worries, your body will literally take care of it as soon as it starts.

Amazing.

CO2 levels in the blood will rise when running a marathon as a product of cellular metabolic processes (called cellular respiration); it forms H2CO3 (carbonic acid) in the blood itself by becoming soluble in the plasma part of the blood.As it dissociates into H+ and HCO3-, the H+ ions have a direct effect on the central chemoreceptors in the brainstem (and some peripheral chemoreceptors too) to stimulate the process of ventilation ie breathing thereby eliminating the CO2 which has built up in the blood, via the lungs.

Thats a brief description of what occurs.The level of CO2 in the blood also has an effect on the release of oxygen by its carrier, hemoglobin.As CO2 is acidic when rendered into a solution the kidney also is affected as the kidney is actually most responsible for maintaing the correct pH of the circulating blood.