Cholesterol, LDL and HDL
Cholesterol Carrying Vessels
HDL, and LDL cholesterol is made in the liver. Cholesterol is really an alcohol but because of its complex structure it is water insoluble. Since the blood is a watery mixture, it would be impossible for cholesterol to be delivered by the blood from where it is made to where it is needed.
The liver makes a substance called a lipoprotein which is formed into a miniature “submarine”-like organelle. Its purpose is to form an entity that will carry water-insoluble cholesterol in the watery environment of the blood.
On the exterior of the lipoprotein shell hydrophilic (water-loving) side chains extend out into the blood. These water loving side chains make the lipoprotein shell compatible with the watery blood.
On the interior of the lipoprotein shell are hydrophobic (water hating, or fat loving) side chains. These hydrophobic groups will dissolve the fat soluble cholesterol inside the lipoprotein “submarine”.
The LDL can then deliver water-insoluble cholesterol to cells that need cholesterol through the watery streams of blood.
The “submarine” docks at an LDL receptor on the surface of a body cell needing cholesterol, and cholesterol is unloaded.
The LDL may become an HDL (high density lipoprotein) after unloading cholesterol. Or unused cholesterol may be carried back to the liver by a separate HDL for disposal of the unused cholesterol. I am not able to determine which, if either of these possibilities, is true.
What makes no sense to me is that an entity that delivers a useful and needed commodity, cholesterol, from the liver to the cells that need it, is “bad” cholesterol, but HDL that delivers unused cholesterol from the cells to the liver is “good” cholesterol.
Dr. Ravsnkov sought to unravel the uncertainties from the original data of research studies.
Observations Used to Proclaim Some Cholesterol Good and Some Bad
A number of follow up studies have shown that a lower than normal level of HDL-cholesterol and a higher than normal level of LDL-cholesterol are associated with a greater risk of having a heart attack.
Or a low HDL/LDL ratio is a risk factor for coronary heart disease.
A higher than normal level of HDL and a lower than normal level of LDL is associated with a smaller risk.
Relatively few people are afflicted with familial hypercholesterolemia, perhaps less than 1% of the population.
Those who carry this genetic error have a defective LDL receptor that prevents the LDL carrier vessel from unloading cholesterol to the body cells.
Those that carry this genetic defect have very high total cholesterol and LDL cholesterol.
These individuals can have heart attacks at a relatively young age. But several studies have shown many of these patients live a normal life span.
The appearance of cholesterol in these individuals is not like atherosclerosis in normal individuals.
The few studies that attempted to deal with “good’ or “bad” cholesterol were not successful in determining unequivocally whether either LDL or HDL cholesterol had any relevance in heart disease, or its prevention.
Risk Factors versus HDL/LDL Ratios: Which is Important?
Smoking, being overweight, having high blood pressure, and emotional stress correlated with increased cholesterol. Emotional stress causes the greatest increase in cholesterol.
A risk factor is not necessarily the same as the cause. Something may provoke a heart attack and at the same time lower the HDL/LDL ratio.
Weight loss causes LDL to go down a little but HDL goes up a little. Is it the change in HDL/LDL ratio that is good or is it weight loss that is good?
Smoking raises LDL cholesterol a little, while HDL goes down resulting in an unfavorable HDL/LDL ratio. But is it the ratio that is bad, or that smoking itself is bad.
Exercise decreases the “bad” LDL, and “good” HDL increases. In well trained individuals HDL increases considerably.
Is it the ratio of HDL/LDL that is important or the exercise an individual gets that’s important.
A low HDL/LDL is associated with high blood pressure. High blood pressure can come from a lot of stress. Stress stimulates the sympathetic nervous system which produces too much adrenaline.
High blood pressure may provoke a heart attack by an adrenaline-induced spasm of the coronary arteries, and at the same time lower the HDL/LDL ratio.
Again it may be asked is it the HDL/LDL ratio that is good, or is it lowering stress that is good?
A calculation of the risk of high LDL cholesterol that does not consider the other risk factors is a univariate analysis and is meaningless.
High Cholesterol Protective for Some
In the elderly high cholesterol seems to be protective stated Dr Harlan Krumholz and coworkers at the Yale University Department of Cardiovascular Medicine. Nine hundred ninety-seven people were followed over a 4 year period. Twice as many individuals had a heart attack or died with CHD who had low cholesterol compared to those who had the highest cholesterol.
A study that did not find HDL to be a good predictor of heart disease included 518 healthy men in Finland over a period of 24 years. This was part of the Seven Countries study which will be discussed in a subsequent page.
West Finland, Initial HDL Cholesterol 43.2 mg/dL, CHD Deaths 105
Helsinki, Initial HDL Cholesterol 44.8 mg/dL, CHD Deaths 81
North Karelia, Initial HDL Cholesterol 47.6 mg/dL, CHD Deaths 183
North Karelia had the highest mean HDL yet had the greatest number of CHD deaths per 1000 men.
West Finland had the lowest initial mean HDL but had the intermediate number of CHD deaths per 1000 men.
Helsinki had the intermediate mean HDL but had the lowest CHD deaths per 1000 men.
In other long lasting studies it was found that healthy survivors had lower HDL-cholesterol levels.
There is no trend that would suggest HDL has any predictive value in CHD deaths.
The problems dogging HDL, and LDL cholesterol as a cause of heart disease continue to be explained.