ABSTRACT
In humans, about two-thirds of plasma cholesterol can be recovered in the low density lipoprotein (LDL) fraction, mostly in esterified form. High density lipoprotein is believed to promote the removal of cholesterol from the cells and mediate its transport centripetally to the liver from where it can be excreted in the bile. LDL receptors seem to be downregulated since it is possible to increase the receptor activity of freshly isolated white blood cells by incubating them in a medium containing lipoprotein-deficient serum. Cholesterol has both structural and metabolic functions in animal cells. It is considered to regulate the membrane fluidity, thereby maintaining a microen-vironment appropriate for the operation of membrane-linked enzymes and transport proteins. An examination of age-adjusted cancer incidence rates by serum cholesterol level showed an inverse association between cholesterol and all cancer, lung, colorectal, pancreatic, bladder cancer, and leukemia.
