What causes low HDL cholesterol levels?

Smoking, not getting enough physical activity and eating a diet high in refined carbohydrates are some of the reasons for a low HDL cholesterol level, notes Harvard Medical School. High-density lipoproteins are particles that carry cholesterol.

HDL is known as good cholesterol, but not all HDL particles carry cholesterol out of the bloodstream, states Harvard Medical School. Some of these particles actually carry cholesterol into the cells. Genetics play a role in determining whether someone has a low HDL or high HDL level. Being overweight is also linked to low HDL levels. Beta-blockers, progestins, anabolic steroids and other medications affect HDL levels in some people.