First let's know what cholesterol is. Cholesterol is a fatty substance found in our blood. Our body needs cholesterol to build healthy cells. For a child and adult a healthy cholesterol level is under 200 mg/dl. Cholesterol levels over 200 mg/dl is considered high cholesterol. High cholesterol is a medical condition called hyperlipidemia. Hyperlipidemia is mainly caused by not exercising enough, being overweight, eating lots of fatty foods and it can also run in our genes. Too much cholesterol can block your blood vessels causing heart problems or even a stroke.