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Rise of good cholesterol can reduce cardiovascular risks
Cholesterol is a waxy fat (lipid) carried through blood by lipoproteins. The two main types of lipoproteins are high density lipoproteins (HDLs) and low density lipoproteins (LDLs). HDLs (good cholesterol) carry LDLs (bad cholesterol) away from artery walls. LDLs stick to artery walls and can lead to plaque build-up (atherosclerosis).
Persons with low HDL (Low Density Lipoprotein) cholesterol levels (less than 40 mg per deciliter [1.03 mmol per liter] in men and less than 50 mg per deciliter [1.30 mmol per liter] in women) are at increased risk of coronary heart disease, restenosis (conditions where coronary vessels become narrow repeatedly) after angioplasty, and death from cardiovascular causes, especially if such persons are male or have diabetes. Often, persons with low HDL cholesterol levels also have other cardiovascular risk factors, such as diabetes, hypertension, or both, which further increase risk.
HDL cholesterol transports excess cholesterol from peripheral tissues to the liver for excretion, a process known as reverse cholesterol transport. In addition, HDL cholesterol inhibits the oxidation of LDL cholesterol and the expression of cellular adhesion molecules and monocyte recruitment, and it may reduce the risk of thrombosis (blood clotting or blocking of an artery or vein by a mass of coagulated blood) by inhibiting platelet activation and
aggregation.
Lifestyle modifications
Exercise: Regular aerobic exercise increases the HDL cholesterol level by 3 to 9 percent in healthy, sedentary persons. This increase is related to the frequency and intensity of physical activity, with greater increases in HDL cholesterol occurring with frequent,
low-intensity exercise (e.g., five 30-minute sessions per week vs three 60-minute sessions). However, there is little evidence that walking significantly increases HDL cholesterol levels. HDL cholesterol levels may increase with as little as eight weeks of regular exercise.
Regular exercise yields greater increases in HDL cholesterol in men with low HDL cholesterol levels, elevated triglyceride levels, and abdominal obesity than in those with isolated low HDL cholesterol levels. Weight loss may be crucial for an increase in HDL cholesterol to occur.
Improvement in HDL cholesterol levels associated with exercise, and weight loss is greatest in persons with the highest baseline HDL cholesterol levels (60 mg per deciliter [1.55 mmol per liter] or more); those with low baseline levels have less improvement.
Smoking cessation: Cigarette smoking is associated with reduced HDL cholesterol. After smoking cessation, HDL cholesterol increases (by a mean of 4mg per deciliter [0.10 mmol per liter]), more so in women than in men and in persons with elevated baseline HDL cholesterol levels (>47 mg per deciliter [1.21 mmol per liter]).
Weight control: Obesity is associated with reduced HDL cholesterol levels and elevated serum triglyceride levels. A negative correlation exists between HDL cholesterol and body-mass index.
A reasonable weight-loss goal for overweight or obese patients is 1lb (0.45 kg) per week, with a target body-mass index of less than 25.
Dietary fat intake: Plasma LDL (Loe Density Lipoprotein) cholesterol and HDL cholesterol levels decline with reductions in the intake of dietary fat.
The concomitant decrease in LDL
cholesterol that occurs with a diet low in saturated fat may override the effects associated with the decline in HDL cholesterol. A diet rich in n-3 polyunsaturated fatty acids -sources include oils (olive, canola, soy, flaxseed), nuts (almonds, peanuts, walnuts, pecans), cold-water fish (salmon, mackerel), and shellfish -- with limited carbohydrates that contribute a high glycemic (glucose in blood) load (such as those found in ready-to-eat cereals, potatoes, white bread, and snack foods) can be recommended to increase serum HDL cholesterol levels.
Medication
Several classes of medications increase HDL cholesterol levels; these include niacin and fibrates, in particular, and, to a lesser degree, statins. These medications also lower triglycerides and LDL cholesterol levels.
In some patients with low HDL cholesterol levels, various lipid-modifying medications may be useful in combination.
Guidelines from professional associations
The National Cholesterol Education Program emphasises that initial treatment should be directed toward achieving a target LDL cholesterol level (and non-HDL cholesterol if the triglyceride level is more than 200 mg per deciliter [2.26 mmol per liter]) before considering niacin or fibrates in persons with low HDL cholesterol levels.
The American Diabetes Association recommends that adults with diabetes should first aim for an LDL cholesterol level of less than 100 per deciliter (2.59 mmol per liter); secondary targets should include an HDL cholesterol level of more than 40 mg per deciliter and a triglyceride level of less than 150 mg per deciliter (3.88 mmol per liter). Caution is recommended with regard to the use of high-dose niacin in patients with diabetes, because this may increase glucose levels.
Summary and recommendations
A low level of HDL cholesterol is an independent risk factor for future cardiovascular events. A compre-
hensive approach to achieving optimal HDL cholesterol levels (40 mg per deciliter or more in men and 50 mg per deciliter or more in women) should include lifestyle modifications, followed by the consideration of pharmacotherapy in high-risk patients.
Lifestyle changes should be recommended as the first approach to raise HDL cholesterol levels, which would lead to other cardiovascular benefits.
We would initially recommend a programme of regular aerobic exercise (a gradual increase to 30 minutes of brisk aerobic activity five days per week), weight loss (1 lb per week, with a target body-mass index of less than 25), and the substitution of sources of polyunsaturated fats such as oils (olive, canola, soy, flaxseed), nuts (almonds, peanuts, walnuts, pecans), cold-water fish (salmon, mackerel), and shellfish for saturated fats and simple carbo-hydrates. Persons who smoke should be advised to quit. Moderate alcohol intake is reasonable for patients who so choose and for whom there are no contraindications.
Whether to add medication to lifestyle changes to raise HDL cholesterol levels will depend on the degree of cardiovascular risk.
The article was first published in the New England Journal of Medicine, September 22, 2005 issue. The original article was modified while published in Star Health.