LDL cholesterol is informally known as “bad” cholesterol. Usually, doctors encourage people to lower LDL cholesterol levels. However, when LDL levels fall below 50 milligrams per deciliter (mg/dL) of blood, this may signal a health problem or cause symptoms.

Low LDL cholesterol is less common than low HDL cholesterol. Typically, it is secondary to another medical condition, such as:

• malnourishment from poor nutrition, or from disorders that affect a person’s ability to absorb nutrients
• hyperthyroidism
• chronic infections, such as hepatitis C
• chronic inflammation
• blood cancers

Three genetic disorders may cause low LDL cholesterol:

• Hypobetalipoproteinemia: A person must inherit two copies of a gene for this condition to develop. It causes the body to metabolize LDL very quickly. Some people with this disorder have no detectable levels of LDL and need treatment. Others have low but detectable LDL levels and do not usually need treatment.
• Chylomicron retention disease: To develop this condition, a person has to inherit two copies of a certain gene – one from each parent. Symptoms usually present in infancy and can cause nutritional malabsorption, failure to thrive, and fatty stools. It is also known as Anderson’s disease.
• Abetalipoproteinemia: This condition, also known as Bassen-Kornzweig syndrome, means a person cannot absorb fat from their diet. Babies usually show symptoms and may have a very low weight, intellectual disabilities, and failure to thrive.

Low LDL cholesterol may also occur if a person is taking cholesterol-lowering medication.