Cholesterol - Cholesterol is a major precursor of cholesterol ester, bile acids, and steroid hormones and is a component of plasma membranes. It is a necessary component of all cell membranes. It is the precursor to all steroid hormone (including estrogen , testosterone , cortisol , and vitamin D ). It is the leading organic molecule in the brain and is needed for brain function. However, too much cholesterol in the bloodstream can be unhealthy, it builds up in the artery wall and can lead to the signs and symptoms of coronary heart disease.