Calcification of the aortic valve
What causes calcification of the aortic valve in the elderly? Hypercalcemia??
If I may, I'll rephrase your question to be,
"What causes atherosclerosis?" Atherosclerosis is the term for
hardening of the blood vessels. "Calcification" implies too great a
role for calcium in the process of atherosclerosis. Although calcium is
found in atherosclerotic legions (PLAQUES), it's probably an innocent
bystander, which go caught up in a larger process, as we shall see ...
The most popular theory of atherosclerosis today is the
"Response to Injury" hypothesis, which goes as follows ...
1) First, damage to the intima occurs. The INTIMA is the inner
layer of cells of the blood vessels. It can be damaged by myriad
factors, such as toxins, viruses, insufficient oxygen, over-active
enzymes, auto-antibody attack, and free radicals. Since your question
was specifically concerning the elderly, the last cause, FREE RADICALS,
may play a large role. Free radicals are very reactive substances which
damage (OXIDIZE) normal cells. The body usually has sufficient defenses
against free radicals (called ANTIOXIDANTS), but aging does decrease our
antioxidant capabilities. Thus, unchecked free radical damage (OXIDATION)
in the blood may cause damage to the intima of blood vessels.
Furthermore, unhealthy habits such as smoking introduce great amounts
of free radicals into the blood. Also, diets rich in cholesterol and d
saturated fat increase blood levels of lipoproteins, the carriers of
cholesterol, which encourage oxidation.
2) Next, the immune system responds to the damage, just as it would
if you had cut your finger... MONOCYTES rush to the site and become
MACROPHAGES which gobble up (PHAGOCYTIZE) fat particles until they
swell up into FOAM CELLS. Furthermore, PLATELETS attach to the injury
site and initiate the INTRINSIC pathway for blood clotting. (Here's
where calcium comes into the picture: calcium is essential in the
blood clotting mechanism.) All these immune cells release GROWTH FACTORS
which cause smooth muscle to form.
3) The result of all this activity forms a PLAQUE, or a hardened
legion in the blood vessel. It is essentially a messy internal blood clot!
If encouraged to grow, plaque build-up continues and may clog up
vessels. Circulation is thus compromised. If the clot occurs in a vessel
leading to the heart, heart tissue starve, die, and this causes a
heart attack. In the brain, it would cause a stroke.
Continuing to smoke or eat high fat/high cholesterol diets, as
we saw, encourages plaque growth.
Applied to the elderly, plaques may continue to grow unannounced
throughout our lives, until one day, after many years, they may
block enough of the circulation to cause health problems.
This theory, if true, might explain why some health authorities
claim that taking antioxidant vitamins may help prevent atherosclerosis
and heart disease. Several studies have just been completed which
strongly suggest taking extra vitamin E and vitamin C, the main anti-
oxidant nutrients, significantly reduces the risk of heart disease death
in men. Another study showed that low blood levels of vitamin E is
a more important risk factor in heart disease death than high blood
levels of cholesterol!
Here are some references for further reading:
The Pathogenesis of Atherosclerosis, by Russell Ross, New England
Journal of Medicine, Vol. 314, Number 8, pages 488-500.
Inverse correlation between plasma vitamin E and mortality from
ischemic heart disease in cross-cultural epidemiology, by KF Gey, et al.
The American Journal of Clinical Nutrition, 1991, Vol. 53.(supplement)
pages 326 S - 334 S.
Vitamin E supplementation and risk of coronary heart disease among men.
by EB Rimm, et al. Circulation, 1992, vol. 86: I-463.
A prospective study of vitamin E supplementation and risk of coronary
disease in women. MJ Sampfer, et al. Circulation, 1992; vol.86, I-463.
Click here to return to the Biology Archives
Update: June 2012