HDL > 1.04 mmol/L is the normal range, and when HDL ≤ 1.0 mmol/L means low HDL in the body. There are many causes of low HDL in the body. Firstly, low HDL is commonly caused by cardiovascular diseases, such as cerebrovascular disease, coronary heart disease and hypertension, where lower than normal HDL is one of the common clinical manifestations. Secondly, low high-density cholesterol is considered to be caused by liver damage, such as acute and chronic hepatitis, liver cirrhosis, and liver cancer. Certain diseases or daily factors, such as diabetes, thyroid disease, lack of exercise, smoking, and alcohol consumption, are not excluded. Low high-density cholesterol in human body is considered to be caused by pathological factors, so promptly go to the hospital for examination and targeted treatment.