Anemia can be due to a condition present at birth (congenital) or to a condition you develop (acquired). Anemia occurs when your blood doesn't have enough red blood cells.
This can happen if:
• Your body doesn't make enough red blood cells
• Bleeding causes you to lose red blood cells more quickly than they can be replaced
• Your body destroys red blood cells
What red blood cells do?
Your body makes three types of blood cells — white blood cells to fight infection, platelets to help your blood clot, and red blood cells to carry oxygen from your lungs to the rest of your body and carbon dioxide from the body back to the lungs.
Red blood cells contain hemoglobin — an iron-rich protein that gives blood its red color. Hemoglobin enables red blood cells to carry oxygen from your lungs to all parts of your body and to carry carbon dioxide from other parts of the body to your lungs to be exhaled.
Most blood cells, including red blood cells, are produced regularly in your bone marrow — a spongy material found within the cavities of many of your large bones. To produce hemoglobin and red blood cells, your body needs iron, vitamin B-12, folate and other nutrients from the foods you eat.
Courtesy: Mayo Clinic