Cholesterol is a waxy substance that circulates in blood in a complex with protein called a lipoprotein. Low-density lipoprotein, or LDL, is a bad form of cholesterol, because in excess it raises your risk for coronary artery disease, heart attack and stroke. Nevertheless, cholesterol is also needed by your body for many metabolic processes, so keeping your blood levels in a healthy range is important both to prevent disease and allow your body to function properly. Consult your doctor or a registered dietitian to develop a dietary regimen appropriate for you.
Your body obtains cholesterol from the food you eat or from cells that make it from raw materials. Cholesterol is needed by every cell in your body as a component of the cell membrane that surrounds it. It helps to stabilize the cell membrane, making it less fluid and more impermeable to external molecules. Cholesterol is also a component of the membranes of some organelles inside the cell that produce energy and synthesize proteins.
Cholesterol is a precursor to one of the most important vitamins, vitamin D. Manufacture of vitamin D occurs in the skin, triggered by exposure to sunlight. The ultraviolet B rays in sunlight act as a co-factor for vitamin D production, which requires cholesterol as a starting material. Although fortified foods and some animal foods such as meat and eggs provide small amounts of vitamin D, your body depends significantly on its own ability to produce this important vitamin from cholesterol.
Cholesterol is the basic building block of all steroid hormones. These include the sex hormones, testosterone, made mainly in the testes in men, and estrogen and progesterone, made mainly in the ovaries in women. Men's bodies make some estrogen and progesterone, and women's bodies make some testosterone -- but in much smaller quantities. Cortisol and aldosterone are also steroid hormones, produced in the adrenal gland and crucial for regulation of blood pressure, responding to stress, maintenance of salt and water balance and proper function of your immune system. For each hormone, cholesterol is modified in a specific way by cells of these organs.
Bile acids are specialized compounds manufactured in the liver from cholesterol. They are very important in allowing your digestive system to break down fats. When you eat, bile acids are released into the intestines as part of bile. These molecules have special characteristics that allow them to form a bridge between fat molecules and water. This emulsifies the fat, making it soluble in the intestinal fluid where enzymes are able to break it down.