LDL cholesterol is called “bad” cholesterol because elevated levels of LDL cholesterol are associated with an increased risk of coronary heart disease. LDL lipoprotein deposits cholesterol on the artery walls, causing the formation of a hard, thick substance called cholesterol plaque. Over time, cholesterol plaque causes thickening of the artery walls and narrowing of the arteries, a process called atherosclerosis. High amounts of the bad LDL will deposit cholesterol on the artery walls forming plaques. More and more plaques will narrow the arteries lumen and may eventually block blood flow. Therefore LDL is considered the “bad” cholesterol.

Saturated fats and trans fatty acids are the most important factors that raise blood cholesterol, not dietary cholesterol! Monounsaturated fats and polyunsaturated fats found in nuts and fish for instance, can lower the LDL level. In addition, soluble fiber found in fruits, oats, barley and legumes can also lower LDL.

HDL cholesterol is called the “good cholesterol” because HDL cholesterol particles prevent atherosclerosis, by extracting cholesterol from the artery walls and disposing of them through the liver. Thus, high levels of LDL cholesterol and low levels of
HDL cholesterol (high LDL/HDL ratios) are risk factors for atherosclerosis, while low levels of LDL cholesterol and high level of HDL cholesterol (low LDL/HDL ratios) are desirable.

Physical activity can also raise HDL level. Total cholesterol is the sum of LDL (low density) cholesterol, HDL (high density) cholesterol, VLDL (very low density) cholesterol, and IDL (intermediate density) cholesterol. HDL cholesterol extracts cholesterol particles from the artery walls and transports them to the liver to be disposed through the bile. It also interferes with the accumulation of LDL cholesterol particles in the artery walls.

The risk of atherosclerosis and heart attacks in men is strongly related to HDL cholesterol levels. Low levels of HDL cholesterol are linked to a higher risk, whereas high HDL cholesterol levels are associated with a lower risk. Very low and very high HDL cholesterol levels can run in families. Families with low HDL cholesterol levels have a higher incidence of heart attacks than the general population, while families with high HDL cholesterol levels tend to live longer with a lower frequency of heart attacks. Like LDL cholesterol, lifestyle factors and other conditions influence HDL cholesterol levels. HDL cholesterol levels are lower in persons who smoke cigarettes, eat a lot of sweets, and are overweight and inactive; and in patients with type II diabetes mellitus.

HDL cholesterol is higher in people who are lean, exercise regularly, and do not smoke cigarettes. Estrogen increases a person’s HDL cholesterol, which explains why women generally have higher HDL levels than men do. For individuals with low HDL cholesterol levels, a high total or LDL cholesterol blood level further increases the incidence of atherosclerosis and heart attacks. Therefore, the combination of high levels of total and LDL cholesterol with low levels of HDL cholesterol is undesirable whereas the combination of low levels of total and LDL cholesterol and high levels of HDL cholesterol is favorable.