Final answer:
Erythropoietin (EPO) is a hormone produced by the kidneys that stimulates the production of red blood cells, and its misuse in sports as a performance enhancer is banned.
Step-by-step explanation:
The hormone that helps regulate red blood cell production is Erythropoietin (EPO). EPO is a glycoprotein hormone secreted by the kidneys in response to low oxygen levels in the blood. It stimulates the bone marrow to produce more red blood cells, which carry oxygen throughout the body. While it can be medically beneficial for treating certain types of anemia, athletes have used EPO for performance enhancement, known as blood doping, which is banned in sports due to health risks such as blood clots and heart-related issues.