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. [See Box Consequences
of Low Cholesterol Levels.]
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. 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. |
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. [See Box Consequences of Low Cholesterol
There has been research suggesting an association between high cholesterol levels
and Alzheimer's disease (AD) in some people. The major target in genetic research
on late-onset 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. A
number of recent studies support the link between Alzheimer's disease and cholesterol
by suggesting that certain cholesterol-lowing drugs statin drugs known as statins
may be protective against AD. (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. 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, however, that this
higher death rate is almost totally due to lung cancer in smokers with low
Effects of Natural Low Cholesterol Levels. 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:
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 acids. Low levels of omega-3s, which are found
in oily fish, 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.
- One study found that male psychiatric patients with cholesterol below
160 mg/dl had twice the normal rate of suicide and that elderly men
with low cholesterol levels had three times the normal risk of depression.
- Another 2000 study supported earlier work on an association between
depression and chronically low cholesterol levels.
- 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.
Effects of Medication-Induced Low Cholesterol Levels. Importantly,
numerous studies have reported no association between the use of
cholesterol-lowering drugs and depression or rates of suicide, accidents,
or violent death.
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).
Definition of Cholesterol, Other Lipids, and
Lipoproteins, Effects of Cholesterol
and Lipids on the Heart, Effects of Cholesterol and Lipids on the Brain,
Risk Factors for Unhealthy Lipid
Levels, Symptoms of Unhealthy Levels
of Cholesterol, Diagnosis and Screening,
Lifestyle Modifications, Drug
Treatments, Support Organizations
©2002 A.D.A.M., Inc. (or its subsidiaries)