June 30, 2003
A: FROM MENTOR JOAN LUSK IN RI
Basically, it's a combination of heredity, diet and exercise. We
make our own cholesterol, even more than we get from eating a normal
diet. Reducing the amount in the diet sometimes lowers the level in
the blood, but some people keep on making more. Biosynthesis is
subject to feed-back inhibition by cholesterol - perhaps individual
variation in responses to diet may be attributed to variability in
this control mechanism, but I haven't seen that stated. Some
cholesterol is converted to "bile acids", detergent-like molecules
that help solubilize lipids in the gut so they can be absorbed. A
small fraction of bile acids are excreted, which is the only way to
eliminate cholesterol from the body; this route can't handle a big
excess of dietary cholesterol. Some cholesterol-lowering drugs
promote increased excretion of cholesterol.

Low-density lipoproteins (LDL) are important in carrying cholesterol
out into the blood and high density (HDL) are important in removing
it from the blood. For some reason that I don't understand, exercise
increases HDL lowers LDL, and hence lowers cholesterol. I don't know
whether lack of exercise can explain the typical rise of cholesterol
levels with age. After menopause, women's LDL levels rise and so
does their cholesterol.

A site with a medical point of view:
http://www.nhlbi.nih.gov/health/public/heart/chol/wyntk.htm
A site with a biochemical point of view.
http://www.indstate.edu/thcme/mwking/cholesterol.html#regulation

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A: FROM MENTOR DIANA DIONISIO IN CA
There are two types of cholesterols. HDL (high density lipo-protein) and LDL (low density etc.). When you eat foods with cholesterol, LDL is the bad one that can be deposited in your arteries and clog it to lead to high blood pressure and eventually blockage if it gets to bad. HDL is good cholesterol and actually helps to stop the deposits and makes it better.