HDL cholesterol of 0.9 mmol/L is a reduced level. HDL cholesterol is often referred to as “good cholesterol” because an increase in its level facilitates the removal of cholesterol from peripheral tissues, thereby preventing the occurrence of atherosclerotic diseases such as cerebral infarction and coronary heart disease, and is therefore considered an anti-atherosclerotic factor. HDL cholesterol less than 1.16mmol/L is a reduced level. In this case, it is recommended to improve the lifestyle, including avoiding fatty diets, quitting smoking and drinking, and exercising appropriately; on the other hand, it is recommended to accept lipid-lowering drugs such as statin therapy when necessary. If necessary, consult a doctor in time for standardized diagnosis and treatment.