Increased LDL is one of the risk factors for atherosclerosis, and increased LDL levels are associated with an increased risk of heart disease. The clinical level of LDL is mostly reflected by the level of LDL cholesterol. The normal level of LDL cholesterol is less than 3.4 mmol/L (130 mg/dl), and if it is higher than 3.4 mmol/L in a healthy person, the LDL is high. Factors that may lead to elevated LDL include unhealthy diet, overweight, lack of physical activity, smoking, and genetics. In addition, certain medications and certain diseases can also cause LDL to be elevated. The main function of LDL is to transport cholesterol from the liver to extrahepatic tissues, so an increase in LDL can cause elevated cholesterol in the blood. LDL is also more likely to be deposited on the inner walls of blood vessels, forming atheromatous plaques. This is why it is known as “bad cholesterol”. Its level is associated with increased prevalence of cardiovascular disease and mortality. The normal level of LDL cholesterol is below 3.4 mmol/L (130 mg/dl), but this standard is only appropriate for healthy people. The standard for other special populations is even lower. For example, for atherosclerotic heart disease, it should be <1.8 mmol/L; for diabetes + hypertension or other risk factors, LDL should be <1.8 mmol/L; for diabetes LDL should be <2.6 mmol/L; for hypertension + 1 other risk factor, LDL should be <2.6 mmol/L; for hypertension + 3 other risk factors, LDL should <3.4mmol/L.