Health Hype states that an excess amount of red blood cells affects the viscosity of blood and causes the rate of blood flow to decrease. While the body copes with a slight increase or decrease in the red blood cell concentration within the blood, too many red blood cells or too few red blood cells have a plethora of effects on the human body.
According to the Mayo Clinic, red blood cell production increases either to compensate for low oxygen levels due to poor heart or lung function or to compensate for lower oxygen levels at higher altitudes. Extra red blood cells are also produced when the kidneys release too much of a protein that promotes red blood cell growth. The primary function of red blood cells is to carry oxygen in the bloodstream from the lungs to the cells of the body. The presence of red blood cells in human blood has many different effects on the body and influences the action and function of other parts of the cardiovascular system. Red blood cells contain hemoglobin, a protein that carries 97 percent of the oxygen in the body. The other 3 percent of the body's oxygen is dissolved in the plasma.