Cholesterol's Effect on the Brain
The effect of cholesterol on the brain is complex. High cholesterol has been linked to Alzheimer's disease and a greater risk for certain strokes. Low cholesterol, however, may have some negative effects on the brain.
High Cholesterol and Stroke
Having adequate levels of HDL may be the most important lipid-related factor for preventing ischemic stroke, which is a type of stroke caused by blockage of the carotid arteries, those carrying blood to the brain. HDL may even reduce the risk for hemorrhagic stroke, which is a less common stroke caused by bleeding in the brain and associated with low overall cholesterol levels.
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| The build-up of plaque in the internal carotid artery may lead to narrowing and irregularity of the artery's lumen, preventing proper blood flow to the brain. More commonly, as the narrowing worsens, pieces of plaque in the internal carotid artery can break free, travel to the brain and block blood vessels that supply blood to the brain. This leads to stroke, with possible paralysis or other deficits. |
The effects of high total cholesterol and LDL levels on ischemic stroke are less clear. One study suggested that the risk for ischemic stroke increases when total cholesterol is above 280 mg/dL. A 2002 study suggested that high cholesterol poses a risk for stroke only when specific proteins called ISPs associated with inflammation were present.
High Cholesterol and Late-Onset Alzheimer's Disease (AD)
To date, evidence points to high cholesterol levels, along with hypertension and a family history of the disease, as independent risk factors for AD. A major research target in the investigator for common factors between cholesterol levels and AD has been apolipoprotein E (ApoE), which plays a role in the movement and distribution of cholesterol for repairing nerve cells during development and after injury. People who carry a variant of this gene (ApoE4) are at significantly higher risk for AD. (Other variants may even reduce the risk.)
High cholesterol may pose a risk for Alzheimer's regardless of this genetic factor, however. (Of interest are studies reporting that cholesterol is important within the brain for cell communication and memory, but such benefits do not apply to high cholesterol levels in the blood.)
Consequences of Low Cholesterol Levels
The negative consequences of low cholesterol levels, whether actively lowered or naturally low, are the subject of ongoing debate.
Effects on Mortality Rate
In one study, men with the lowest cholesterol levels had the highest mortality rate, generally due to cancer and other, non-heart related diseases. An analysis of this study along with additional research suggests strongly that this higher death rate is almost totally due to lung cancer in smokers with low cholesterol -- not low cholesterol itself.
Depression and Risk for Violent Death
Some studies have found that cholesterol is important for the production of serotonin, a chemical in the brain that at low levels is associated with depression. Men with naturally low cholesterol levels also have low serotonin levels. Some evidence has reported a link between natural low natural cholesterol levels and negative emotional states, including depression. Some studies have even reported a higher rate of deaths from suicide, accidents, or violence, which could be related to negative emotional states. The following are some of examples of such studies:
- In one study male psychiatric patients with cholesterol below 160 mg/dL had twice the normal rate of suicide and elderly men with low cholesterol levels had three times the normal risk of depression.
- In a large 2001 Swedish study, violent behavior was linked with naturally low cholesterol levels.
- A 2000 study of patients with depression and bipolar disorders found lower cholesterol levels during specific manic or depressive episodes. The study suggested that mood states might produce low cholesterol levels, not vice versa.
- A 2001 study reported a modest increase in deaths from suicide, accident, or trauma in people who lowered their cholesterol with diet or with non-statin drugs.
Importantly, numerous studies have reported no association between the use of cholesterol-lowering drugs (particularly statins) with depression or violent death. Some researchers have observed that people with low cholesterol levels due to medical conditions or alcoholism are often also deficient in dietary fats known as omega-3 fatty acid, which are found in oily fish. Low levels of omega-3 fatty acids are linked with depression and aggression. In fact, some studies in which cholesterol was lowered using diets that included omega-3 fatty acids reported less depression.
Clearly, any link between low cholesterol levels and emotional disorders is uncertain.
Hemorrhagic Stroke
People with overall cholesterol levels below 180 mg/dL may be at risk for hemorrhagic stroke (which is bleeding in the brain), particularly if they also have high blood pressure. It should be noted, however, that this type of stroke is much less common than ischemic stroke (which is caused by artery blockage and may be related to low HDL cholesterol).
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Click the icon to see an image of omega-3 fatty acids. |
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