Can Cholesterol Be Too Low?
For One Kind Of Stroke, Maybe
By Daniel Q. Haney
Associated Press
NASHVILLE, Tenn. -- While off-the-chart cholesterol levels can trigger strokes, a new study raises the possibility that unusually low amounts may sometimes cause them as well.
High cholesterol is always portrayed in public health messages as an undivided evil. A study presented Saturday at the American Heart Association's annual < stroke conference suggests that, in truth, the facts about cholesterol are a little more complicated, even though on balance low cholesterol is still far better than high cholesterol.
For many years, experts have been convinced that too much cholesterol, particularly the variety called low-density lipoprotein, or LDL, increases the risk of heart disease. But the link between cholesterol and strokes is less clear-cut.
The latest study attempted to sort this out by looking separately at the effects of cholesterol on the two kinds of strokes -- bleeding strokes and clot strokes.
It found that very high cholesterol raises the risk of < that result from blood clots in the brain. But it also showed that low cholesterol increases the hazard of the less common but potentially devastating hemorrhagic strokes that result from burst blood vessels in the brain.
The study calculated that the perfect cholesterol level -- at least, for preventing strokes -- is about 200, which coincidentally is the target established by the federal government's National Cholesterol Education Program.
"I swear I didn't plan it that way," said Dr. David L. Tirschwell of Harborview Medical Center in Seattle.
Other experts argued that the study does not change the overriding public health message. Even if low cholesterol carries a small risk, they said, the hazard is vastly overshadowed by its other benefits to the heart and the brain.
By preventing heart attacks and clot strokes, "lowering cholesterol far, far outweighs the potential negatives of a hemorrhagic stroke," said Dr. Philip B. Gorelick of Rush Presbyterian St. Luke's Medical Center in Chicago.
Heart attacks are the leading cause of death in the United States, while strokes are No. 3, striking about 600,000 Americans annually. About 80 percent of < strokes -- what doctors call ischemic strokes -- occur when a blood clot blocks an artery, choking off oxygen and nutrients to a section of the brain. The rest are hemorrhagic strokes and result from ruptured blood vessels that flood the brain with blood.
Tirschwell studied 587 victims of ischemic strokes and 137 victims of hemorrhagic strokes and compared them to 3,743 healthy people. Among the findings:
* People with cholesterol over 280 were twice as likely as those at 230, the group's average, to have an ischemic stroke.
* People with cholesterol under 180 had double the risk of those at 230 for a hemorrhagic stroke.
* High cholesterol probably accounts for 10 percent to 15 percent of ischemic strokes. Low cholesterol is the cause of perhaps 7 percent of hemorrhagic strokes.
"Our data imply that for stroke, an optimal level may be around 200," Tirschwell said.
While no one knows precisely how low cholesterol might contribute to hemorrhagic stroke, Tirschwell said one possibility is that cholesterol is needed to keep blood vessels strong to prevent rupture.
Heart association vice president Dr. Rodman Stark criticized the study for failing to break down people's cholesterol into the bad LDL and the good HDL, which protects the arteries.
"Even if you accept his conclusion is true, which I don't think was justified, you might still accept a slightly increased risk of hemorrhagic stroke in order to significantly reduce the risk of ischemic stroke, which is four-fifths of the stroke burden," he said.