When they are healthy, the kidneys produce EPO (erythropoietin), which is a hormone that promotes more red blood cells that transfers the oxygen where needed. If the number of red blood cells is lowered, then fatigue is going to occur and will influence over the brain and muscles function, too.
Shortness of breath
If the body is not supplied with enough amount of oxygen, it’s because of the small number of red blood cells which bring the oxygen everywhere. The blood cells number is linked with harmful toxins piled up in the lungs.