HDL is the group of lipoproteins with the highest particle density in serum, with 50% protein and 50% lipid. The level of HDL cholesterol can reflect the level of HDL. Decreased HDL cholesterol refers to plasma concentration below 1mmol/L (40mg/dl). Factors that may lead to decreased HDL cholesterol include diabetes, nephrotic syndrome, poor lifestyle habits, application of certain drugs, etc., as follows: 1. Diabetes and nephrotic syndrome Increased blood glucose in diabetes may decrease HDL levels and increase triglycerides and LDL levels. In patients with nephrotic syndrome, lipid metabolism is abnormal and HDL cholesterol may be normal or reduced. (1) Diet: A diet containing a large amount of saturated fatty acids (such as lard) and refined carbohydrates (such as semolina and white sugar) may reduce HDL cholesterol levels. (2) Smoking: Active or passive smoking may reduce HDL cholesterol levels. (3) Physical inactivity and overweight: Physical inactivity and obesity may reduce HDL cholesterol levels. 3.Drugs Some specific types of beta-blockers, anabolic steroids such as androgens, progesterone, benzodiazepines (for anxiety and insomnia) may reduce HDL levels. 4. Genes Low HDL is also associated with certain genetic disorders, such as familial low alpha lipoproteinemia.