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The good, the bad, the ugly: facts about cholesterol

I. Sathyamurthy

It is often said that the tongue knows not what cholesterol can do to the heart. The high rates of death from heart attack testify to this.

Lipid (fat) measurement is important to predict and help prevent heart attacks. Blood lipids are classified according to their density as high, intermediate and low density lipids. Most of the blood cholesterol is carried as low density particles. These lipids have a protein coating called lipoproteins that carry them. Basically, low density cholesterol (LDLc) is ugly cholesterol and triglycerides (TGL) are bad cholesterol and they are harmful (atherogenic). High density cholesterol (HDLc) is protective and is called good cholesterol. Atherogenic cholesterols have a protein layer coating called ApoB, while good cholesterol contains Apo A1.

LDL cholesterol can further be divided into large, dense and small dense particles. Small, dense particles are highly atherogenic and can penetrate the inner wall of blood vessels readily. There is a type of LDL cholesterol called Lp(a), and in some studies it was shown to be highly atherogenic if its level is more than 30mg/dl. Many studies have shown that ApoB concentrations and the ratio of ApoB to ApoA1 are important predictors of heart attacks. But some older studies showed that a simple ratio of total cholesterol to HDL of more than 5, predicted a high risk of heart disease.

Many modern-day diagnostic laboratories display a menu that features tests for total cholesterol (TC); high density cholesterol (HDLc); triglycerides (TGL); low density cholesterol (LDLc); ApoA1; ApoB;.very low density cholesterol (VLDL) and Lp (a). What one basically should know is that TC levels should be less than 200 mg per cent, TGL levels less than 150 mg per cent and LDLc levels should be less than 130 mg per cent if there is no history of heart disease. In someone who has already had a cardiac event, LDL should be less than 100 mg per cent. For very high-risk individuals, LDL should be less than 70mg per cent. For those who have had a cardiac event (and whose concern should be secondary prevention) the lower the LDL, the better. HDL cholesterol should be greater than 40 mg per cent in men and greater than 50 mg per cent in women.

Twelve-hour fasting is essential for TGL measurement, LDLc. To measure TC and HDL cholesterol, fasting is not essential. For population studies the measurement of these components is enough. If you subtract HDLc (good) cholesterol from total cholesterol you will get the total amount of atherogenic (harmful) lipids. HDLc is antiatherogenic. If bad cholesterol levels are normal, HDL levels are of no concern even if they are low. In Indians it is often reported that HDL levels are usually low and do not increase despite regular exercises, reduction in alcohol intake, cessation of smoking and dietary discipline. In such cases, statins alone are not enough.

Lipid levels can be raised due to a high fat-diet: what are referred to as exogenous lipids. Those who do not have a high-fat diet can still have high blood lipid levels owing to abnormal endogenous lipoprotein metabolism in the liver. A thin-looking individual can have high lipid levels. On the contrary, an obese individual can have a normal lipid level. It all depends on body metabolism.

Footprints of premature atherosclerosis begin in childhood. The progression and the rapidity of progression depend on lipid levels and other risk factors such as high blood pressure, diabetes, effects of smoking and dietary indiscipline. Familial hypercholesterolemia is one of the commonest causes of increased blood lipids in childhood, and usually there is a family history of premature heart disease and sudden death. People with a family history of premature heart attacks (that occur below 40 years), a family history of sudden death, childhood obesity, and with familial hypercholesterolemia and diabetics with high lipid levels, should be strict about their diet in containing exogenous fat intake.

Statins are drugs given to lower lipid levels. They also have anti-inflammatory properties, improve endothelial function (inner layer of blood vessels), stabilise plaques (fatty deposits in the vessel wall) and have antioxidant properties. The side-effects are muscle weakness, elevation of liver enzymes, impaired cognitive function and depression. Recently, after the publication of an article in the media there were apprehensions among patients about depression relating to statin use. It only occurs when high doses are given over long periods, particularly in the elderly, that too among those who are prone to depression. Judicious use of statins under medical supervision is safe.

(I. Sathyamurthy, an interventional cardiologist, is Director of the Department of Cardiology, Apollo Hospitals, Chennai. He was conferred the Padma Shri in 2000, the B.C. Roy National Award in 2002 and a D.Sc (Honoris Causa) from the Dr. M.G.R. Medical University in 2008).

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