Cholesterol is a waxy, fat-like substance that is produced by the liver and is present in many foods. It is a vital component of cell membranes and is necessary for the production of hormones, vitamin D, and bile acids that help digest fats. Cholesterol is transported in the bloodstream by particles called lipoproteins.

There are two types of lipoproteins that transport cholesterol: low-density lipoprotein (LDL) and high-density lipoprotein (HDL). LDL is often called "bad" cholesterol because it can contribute to the buildup of plaque in the arteries, which can lead to heart disease and stroke. HDL is often called "good" cholesterol because it helps remove excess cholesterol from the bloodstream and carries it back to the liver to be eliminated from the body.

While high levels of cholesterol can contribute to heart disease, cholesterol itself is actually a vital substance that is essential for numerous functions in the body. Cholesterol plays a crucial role in building and maintaining cell membranes, as well as helping to produce hormones, vitamin D, and bile acids that aid in the digestion of fats.

Cholesterol is also a critical component of the brain and nervous system, where it helps with the formation and maintenance of synapses, the connections between neurons that enable communication and memory.

Moreover, research has suggested that higher levels of HDL or "good" cholesterol are associated with a lower risk of heart disease and stroke, as HDL can help remove excess cholesterol from the bloodstream and transport it back to the liver to be eliminated from the body.