Cholesterol is a waxy substance that contributes to the buildup of deposits, known as plaques, within blood vessels. Plaques can accumulate in the coronary arteries, which supply oxygen to the heart, and in the carotid arteries, which supply oxygen to the brain.
Along with high blood pressure, diabetes, smoking, and obesity, high cholesterol levels are well-established as a risk factor for coronary heart disease for both men and women. Like these other factors, cholesterol is also a concern for stroke.
Just as a heart attack can occur when one of the coronary arteries becomes narrowed and blocked, a stroke or “brain attack,” can result from the blockage of an artery that supplies oxygen to the brain. However, early research in this area has yielded mixed conclusions on the role of cholesterol in stroke.
A Complicated Story
The connection between cholesterol and stroke is complicated because their relationship varies based on the type of stroke and the type of cholesterol involved.
There are two major types of stroke. The most common type of stroke, ischemic stroke, is caused by the blockage of blood flow. The risk factors for ischemic strokes, including high cholesterol, are the same as those coronary heart disease.
The other major type of stroke, hemorrhagic stroke, is caused by the rupture of a blood vessel, which bleeds into the brain. However, for this type of stroke, elevated cholesterol actually tends to reduce stroke risk. For ischemic stroke, on the other hand, elevated cholesterol levels are a risk factor – not the biggest, perhaps, but certainly a risk factor.
Another significant complication: Not all cholesterol is the same. Different types of cholesterol can have very different effects on the body. LDL is the “bad cholesterol” in terms of its potential for harming the heart and brain and is a major contributor to arterial plaque development. Levels of LDL cholesterol greater than 130 milligrams per deciliter (mg/dL) are linked to an increased risk for ischemic stroke.
HDL, on the other hand, is the “good cholesterol.” HDL levels greater than 35 mg/dL protect against ischemic stroke by helping ferry LDL to the liver and out of the bloodstream and by helping stabilize existing plaques. Higher levels of HDL continue to add protection, with the greatest benefits conferred by HDL levels over 60 mg/dL. On the other hand, HDL levels below 35 mg/dL add to stroke risk.
The Role of Cholesterol-Lowering Medications
Medications used to lower cholesterol levels—in particular, the class of drugs known as statins—have been shown to lower the risk of having a stroke and may reduce the severity of a stroke, if one occurs. By reducing levels of LDL, statins and other cholesterol-lowering drugs help prevent plaque formation and, in turn, stroke and heart disease.
In fact, statins have even been shown to reduce stroke risk in patients with normal cholesterol levels.
Statins also help stabilize existing plaque deposits. Statins help make plaques less fatty and more fibrous, making them more resistant to rupture. When a plaque ruptures, pieces of the plaque break free and are carried away in the bloodstream, where they may lodge in the arteries that supply oxygen to the brain. In addition, the ruptured plaque can trigger the blood to clot, which further increases the risk of blocked blood flow. Statins, however, reduce inflammation and help prevent clots from forming.
Large research studies have drawn clear ties between the use of statins and decreasing stroke risk. One meta-analysis (a study that reanalyzes the results of several other studies) found that statin use reduces stroke risk by 21 percent and that every 10 percent reduction in LDL levels resulted in a 15.6 percent reduction in stroke risk.
Studies of specific statins have shown even more striking results. Several studies have found that while statins offer a general reduction in stroke risk, the greatest benefit is seen in those who have not had a prior stroke. Though statins confer benefits to those who have already had at least one stroke or mini-stroke, the impact is weaker.
Other cholesterol-lowering medications have not matched the record of the statins. However, some small studies have shown protective effects, particularly by helping raise the level of HDL cholesterol. One study of Lopid (gemfibrozil), for example, showed the use of Lopid reduced the risk of stroke by 31 percent with the greatest benefits seen in patients with low initial levels of HDL.
Cholesterol Guidelines for Reducing Stroke Risk
Current guidelines set similar cholesterol goals for reducing the risk of stroke and the risk of coronary heart disease. These guidelines generally recommend that people without existing heart disease who do not smoke and have no other heart disease risk factors (such as diabetes, high blood pressure, obesity, family history of heart disease) should maintain a total cholesterol level of less than 240 mg/dL, with LDL below 160 mg/dL and HDL above 40 mg/dL.
However, people with cardiovascular risk factors are advised to aim for even better cholesterol levels to better protect against heart disease and stroke. These individuals should maintain a total cholesterol level below 200 mg/dL, with LDL below 100 mg/dL, and HDL above 60 mg/dL.